12 - Standard Physics 2, 3, 5 marks

10. Electronics and Communication

SHORT ANSWER QUESTIONS (CONCEPTUAL)

29. What is called electronics?

Electronics is the branch of physics incorporated with technology towards the design of circuits
using transistors and microchips.

It depicts the behaviour and movement of electrons in a semiconductor, vacuum, or gas.
30. What are passive components and active components?

Components that cannot generate power in a circuit are called passive components (e.g.) Resistors,
inductors, capacitors

Components that can generate power in a circuit are called active components. (e.g.) transistors
31. What is energy band?

When millions of atoms are brought close to each other, the valence orbital and the unoccupied
orbital are split according to the number of atoms.

Their energy levels will be closely spaced and will be difficult to differentiate the orbital of one atom
from the other and they look like a band

This band of very large number of closely spaced energy levels in a very small energy range is
known as energy band.
32. What is valance band, conduction band and forbidden energy gap?

The energy band formed due to the valence orbital is called
valence band.

The energy band that formed due to the unoccupied orbital is
called the conduction band

The energy gap between the valence band and the conduction
band is called forbidden energy gap.
33. Define hole.

When an electron is excited, covalent bond is broken.

Now octet rule will not be satisfied.

Thus each excited electron leaves a vacancy to complete bonding.

This ‘deficiency’ of electron is termed as a ‘hole’
34. What is called P-type semiconductor?

The P - type semiconductor is obtained by doping a pure Germanium (or Silicon) crystal with a
dopant of trivalent elements (acceptor impurity) like Boron, Aluminium, Gallium and Indium

In P-type semiconductors, Holes are majority charge carriers and Electrons are minority charge carriers
35. What is N-type semiconductor?

The N - type semiconductor is obtained by doping a pure Germanium (or Silicon) crystal with a
dopant of pentavalent elements (donor impurity) like Phosphorus, Arsenic and Antimony

In N-type semiconductors, Electrons are majority charge carriers and Holes are minority charge carriers
36. Define electron motion in a semiconductor.

In semiconductors, there exists a narrow forbidden energy gap (Eg < 3eV) between the valence band
and the conduction band.

At a finite temperature, thermal agitations in the solid can break the covalent bond between the atoms.

This releases some electrons from valence band to conduction band.

Since free electrons are small in number, the conductivity of the semiconductors is not as high as
that of the conductors.
37. How electron-hole pairs are created in a semiconductor material?

A small increase in temperature is sufficient enough to break some of the covalent bonds and release
the electrons free from the lattice.

Hence a vacant site is created in the valance band and these vacancies are called holes which are
treated to possess positive charges.

Thus electrons and holes are the two charge carriers in semiconductors.
J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 234 K.Gomathi M.Sc., B.Ed
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38. What is P-N junction diode? Give its symbol.

A P-N junction diode is formed when a P is fused
with a N-type semiconductor.

It is a device with single P-N junction
39. What is called biasing? Give its types.

Biasing is the process of giving external energy to charge carriers to overcome the barrier potential
and make them move in a particular direction.

The external voltage applied to the p-n junction is called bias voltage.

Depending on the polarity of the external source to the P-N junction we have two types of biasing
1. Forward bias 2. Reverse bias
40. Differentiate forward bias and reverse bias.
Forward bias Reverse bias

If the positive terminal of the external voltage
If the positive terminal of the battery is
source is connected to the P-side and the connected to the N-side and the negative
negative terminal to the N-side, it is called potential to the P- side, the junction is said to
forward biased be reverse biased

It reduces width of the depletion region.
It increases width of the depletion region.
41. What is mean by break down voltage?

The reverse saturation current due to the minority charge carriers is small.

If the reverse bias applied to a P-N junction is increased beyond a point, the junction breaks down
and the reverse current rises sharply.

The voltage at which this breakdown happens is called the breakdown voltage

It depends on the width of the depletion region, which in turn depends on the doping level.
42. What is called Zener diode? Give its circuit symbol.

Zener diode is a reverse based heavily doped Silicon diode which is specially
designed to be operated in the breakdown region.

The circuit symbol of Zener diode is given below.
43. Give the applications of Zener diode.

Voltage regulators

Peak clippers

Calibrating voltages

Provide fixed reference voltage in a network for biasing

Meter protection against damage from accidental application of excessive voltage.
44. What is opto electronic devices?

The devices which convert electrical energy into light and light into electrical energy through
semiconductors are called opto electronic devices.

Optoelectronic device is an electronic device which utilizes light for useful applications. (e.g.)
LEDs, photo diodes and solar cells.
45. What is light emitting diode (LED)?

LED is a P-N junction diode which emits visible or invisible light whit is
forward biased.

Here electrical energy is converted into light energy, this process is also called
electroluminescence.
46. What is photo diode? Give its circuit symbol.

A P-N junction diode which converts an optical signal into electric current is
known as photodiode

Its operation exactly opposite to that of an LED.

Photo diode works in reverse bias.

The circuit symbol of photo diode is given below.
J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 235 K.Gomathi M.Sc., B.Ed
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47. Give the applications of photo diode.

Alarm system

Count items on a conveyer belt

Photoconductors

Compact disc players, smoke detectors

Medical applications such as detectors for computed tomography etc.
48. Write a note on bipolar junction transistor (BJT).

The bipolar junction transistor (BJT) consists of a semiconductor
(Silicon or Germanium) crystal.

In which an N-type material is sandwiched between two P-type
materials called PNP transistor or a P -type material sandwiched
between two N-type materials called NPN transistor.

The three regions formed are called emitter (E), base (B) and collector (C)

The schematic symbol and circuit symbol of PNP and NPN transistors
are given below.

49. Discuss the different modes of transistor biasing.

(1) Forward Active:

In this bias the emitter-base junction (JEB) is forward biased and the collector-base junction (JCB) is
reverse biased.

The transistor is in the active mode and in this mode, the transistor functions as an amplifier.
(2) Saturation:

Here, both the emitter-base junction (JEB) an collector-base junction (JCB) are forward biased.

The transistor has a very large flow of currents across the junctions.

In this mode, transistor is used as a closed switch.
(3) Cut-off:

In this bias, both the emitter-base junction (JEB) and collector-base junction (JCB) are reverse biased.

Transistor in this mode is an open switch.
50. Give the applications of solar cells.

Solar cells are widely used in calculators, watches, toys, portable power supplies, etc.

Solar cells are used in satellites and space application
Solar panels are used to generate electricity.
51. Draw the circuit diagram of common base configurations of NPN transistor.
Common base configuration:

Input terminal - Emitter

Output terminal - Collector

Common terminal - Base

Input current - IE

Output current - IC

The input signal (VBE) is applied across emitter - base junction

The output signal (VCB) is measured across collector - base junction.
52. Draw the circuit diagram of common emitter configurations of NPN transistor.
Common emitter configuration:

Input terminal - Base

Output terminal - Collector

Common terminal - Emitter

Input current - IB

Output current - IC

The input signal (VBE) is applied across base - emitter junction

The output signal (VCE) is measured across collector - emitter junction.
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53. Draw the circuit diagram of common emitter configurations of NPN transistor.
Common collector configuration:

Input terminal - Base

Output terminal - Emitter

Common terminal - Collector

Input current - IB

Output current - IE

The input signal (VBC) is applied across base - collector junction

The output signal (VEC) is measured across emitter - collector junction.
54. What is called transistor amplifier?

A transistor operating in the active region has the capability to amplify weak signals.
Amplification is the process of increasing the signal strength (increase in the amplitude).
55. Define input resistance of transistor.

The ratio of the change in base-emitter voltage (∆VBE) to the change in base current (∆IB) at a
constant collector-emitter voltage (VCE) is called the input resistance (ri).
∆ 
= 
∆ 

The input resistance is high for a transistor in common emitter configuration.
56. Define output resistance of transistor.

The ratio of the change in collector-emitter voltage (∆VCE) to the change in collector current (∆IC) at
a constant base current (IB) is called the output resistance (ro).
∆ 
 = 
∆ 

The output resistance is very low for a transistor in common emitter configuration.
57. Define forward current gain.

The ratio of the change in collector current (∆IC) to the change in base current (∆IB) at constant
collector-emitter voltage (VCE) is called forward current gain (β).
∆
= 
∆ 

Its value is very high and it generally ranges from 50 to 200.
58. What is the phase relationship between the AC input and output voltages in a common emitter
amplifier? What is the reason for the phase reversal?

The phase relationship between the AC input and output voltages in a common emitter amplifier is 180°


Collector current is  =   ∵  =  


Emitter voltage is  =    
The reason for the phase reversal:
(1) During the positive half cycle:

Input signal (Vs) increases the forward voltage across the emitter-base.

As a result, the base current (IB) increases.

Consequently, the collector current (IC) increases β times.

This increases the voltage drop across RC which in turn decreases the collector-emitter voltage (VCE).

Therefore, the input signal in the positive direction produces an amplified signal in negative
direction at the output. Hence, the output signal is reversed by 180°
(2) During the negative half cycle:

Input signal (Vs) decreases the forward voltage across the emitter-base.

As a result, base current (IB) decreases and in turn increases the collector current (IC).

The increase in collector current (IC) decreases the potential drop across RC and increases the
collector-emitter voltage (VCE).

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 237 K.Gomathi M.Sc., B.Ed

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Thus, the input signal in the negative direction produces an amplified signal in the positive direction
at the output.

Therefore, 180° phase reversal is observed during the negative half cycle of the input signal
59. What is called transistor oscillator?

An electronic oscillator basically converts DC energy into AC energy of high frequency ranging
from a few Hz to several MHz. Hence, it is a source of alternating current or voltage.
Unlike an amplifier, oscillator does not require any external signal source.
60. Give the types of an oscillator.

There are two types of oscillators:
1. Sinusoidal and
2. Non-sinusoidal

Sinusoidal oscillators generate oscillations in the form of sine waves at constant amplitude and frequency

Non-sinusoidal oscillators generate complex non-sinusoidal waveforms like square wave, triangular
wave or saw-toothed wave
61. Give the relation between α and β

Forward current gain in common base mode,
∆

= 
∆ 

Forward current gain in common emitter mode,
∆
= 
∆ 

From the above two equations, we have
 

=  (or)  = 
62. Give the applications of oscillator.

To generate a periodic sinusoidal or non sinusoidal wave forms.

To generate RF carriers.

To generate audio tones

To generate clock signal in digital circuits.

As sweep circuits in TV sets and CRO.
63. Draw the block diagram of an oscillator
Block diagram of oscillator:

Oscillator essentially consists three main parts,
(1) Tank circuit:

The tank circuit generates electrical oscillations and acts as the AC
input source to the transistor amplifier.
(2) Amplifier:

Amplifier amplifies the input ac signal.
(3) Feed back network:

The feedback circuit provides a portion of the output to the tank circuit to sustain the oscillations
without energy loss.

Hence, an oscillator does not require an external input signal.

The output is said to be self-sustained.
64. Distinguish between analog and digital signal.
Analog signal Digital signal

It is continuously varying voltage or current
It contains only two discrete values of voltages
with respect to time (i.e.) low (OFF) and high (ON)

These signals are employed in rectifying
These signals are employed in signal
circuits and transistor amplifier circuits processing, communication etc.,

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LONG ANSWER QUESTIONS (5 Marks)

1. Elucidate the formation of N-type and P-type semiconductors.
N - type semiconductor:

A n-type semiconductor is obtained by doping a pure Silicon (or
Germanium) crystal with a dopant from pentavalent elements like
Phosphorus, Arsenic, and Antimony

The dopant five valence electrons while the Silicon atom has four
valence electrons.

During the process of doping, four of the five valence electrons of the
impurity atom are bound with the 4 valence electrons of the
neighbouring replaced Silicon atom.

The fifth valence electron of the impurity atom will be loosely
attached with the nucleus as it has not formed the covalent bond.

The energy level of the loosely attached fifth electron is found just
below the conduction band edge and is called the donor energy level

The energy required to set free a donor electron is only 0.01 eV for Ge and 0.05 eV for Si.

At room temperature, these electrons can easily move to the conduction band with the absorption of
thermal energy.

The pentavalent impurity atoms donate electrons to the conduction band and are called donor
impurities. Therefore, each impurity atom provides one extra electron to the conduction band in
addition to the thermally generated electrons.

Hence, in an N - type semiconductor,
o the majority carriers – Electrons
o the minority carriers - Holes
P - type semiconductor:

A n-type semiconductor is obtained by doping a pure Silicon (or
Germanium) crystal with a dopant from trivalent elements like Boron,
Aluminium, Gallium d Indium

The dopant has three valence electrons while the Silicon atom has
four valence electrons.

During the process of doping, the dopant with three valence electrons
are bound with the neighbouring three Silicon atoms.

As Silicon atom has four valence electrons, on electron position of
the dopant in the crystal lattice will remain vacant.

The missing electron position in the covalent bond is denoted as a hole.

To make complete covalent, the dopant is in need of one more
electron.

These dopants can accept electrons from the neighbouring atoms. Therefore, this impurity is called
an acceptor impurity.

The energy level of the hole created by each impurity atom is just above the valence band and is
called the acceptor energy level.

For each acceptor atom, there will be a hole in the valence band in addition to the thermally
generated holes.

Hence, in an P - type semiconductor,
o the majority carriers – Holes
o the minority carriers – Electrons

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 244 K.Gomathi M.Sc., B.Ed

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12 - Standard Physics 2, 3, 5 marks
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2. Explain the formation of depletion region and barrier potential in PN junction diode. Discuss
its V–I characteristics.
Formation of PN junction diode:

A P-N junction is formed by joining N -type and P-type
semiconductor materials.

Here the N-region has a high electron concentration and the P-
region a high hole concentration.

So the electrons diffuse from the N-side to the P-side.

Simillarly holes also diffuse from P - side to the N- side. This
causes diffusion current.

In a P-N junction, when the electrons and holes move to the other
side of the junction, they leave behind exposed charges on dopant
atom sites, which are fixed in the crystal lattice and are unable to
move.

On the n-side, position cores are exposed and on the p- side,
negative ion cores are exposed

An electric field E forms between the positive ion cores in the n-
type material and negative ion cores in the p-type material.

The electric field sweeps free carriers out of this region and hence
it is called depletion region as it is depleted of free carriers.

A barrier potential (Vb) due to the electric field E is formed at the junction.

As this diffusion of charge carriers from both sides continues, the negative ions form a layer of
negative space charge region along the p-side.

Similarly, a positive space charge region is formed by positive ions on the n-side.

The positive space charge region attracts electrons from P-side to n-side and the negative space
charge region attracts holes from N-side to P -side.

This moment of carriers happen in this region due to the formed electric field and it constitutes a
current called drift current.

The diffusion current and drift current flow in the opposite direction and at one instant they both
become equal. Thus, a P-N junction is formed.
V -I characteristics:

It is the study of the variation in current through in the respect to the applied voltage across the diode
when it is forward or reverse biased.

Forward bias characteristics:

If the positive terminal of the external voltage source is
connected to the P-side and the negative terminal to the N-
side, it is called forward biased.

A graph is plotted by taking the forward bias voltage (V)
along the x-axis and the current (I) through the diode
along the y-axis. This graph is called the forward V-I
characteristics.

From the graph, at room temperature, a potential difference equal to the barrier potential is required
before a reasonable forward current starts flowing across the diode. This voltage is known as
threshold voltage or cut-in voltage or knee voltage (Vth).
o For Silicon Vth = 0.7 V
o For Germanium Vth = 0.3 V

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The graph clearly infers that the current flow is not linear and is exponential. Hence it does not obey
Ohm’s law.

The forward resistance (rf) of the diode is ratio of the small change in voltage (∆V) to the small
∆
change in current (∆I), ( =
∆

Thus the diode behaves as a conductor when it is forward biased.
Reverse bias characteristics:

If the positive terminal of the battery is connected to the n-
side and the negative potential to the p- side, the junction
is said to be reverse biased.

A graph is drawn between the reverse bias voltage and the
current across the junction, which is called the reverse V -
I characteristics.

Under this bias, a very small current in µA, flows across the junction. This is due to the flow of the
minority charge carriers called the leakage current or reverse saturation current.
o For Silicon Ileakage = 20 µA
o For Germanium Ileakage = 50 µA

Besides, the current is almost independent of the voltage.

The reverse bias voltage can be increased only up to the rated value otherwise the diode will enter
into the breakdown region.
3. Draw the circuit diagram of a half wave rectifier and explain its working.
Half wave rectifier:

In a half wave rectifier circuit, either a positive half or the
negative half of the AC input is passed through while the other
half is blocked.

Only one half of the input wave reaches the output. Therefore,
it is called half wave rectifier.

This circuit consists of a transformer, a P-N junction diode and
a resistor (RL)

Here, a P-N junction diode acts as a rectifying diode.
During positive half cycle of input AC:

Terminal A becomes positive with respect to terminal B.

The diode is forward biased and hence it conducts

The current flows through load resistor RL and the AC voltage
developed across RL constitutes the output voltage Vo
During negative half cycle of input AC:

Terminal B becomes positive with respect to terminal A.

The diode is reverse biased and hence it does not conduct.

No current passes through RL and there is no voltage drop across RL (The reverse saturation current
in a diode is negligible)
Input and Output waveform:

The output waveform is shown below.

The output of the half wave rectifier is not a steady dc voltage but a pulsating wave.

A constant or a steady voltage is required which can be obtained with the help of filter circuits and
voltage regulator circuits.
Efficiency (η) is the ratio of the output dc power to the ac input power supplied to the circuit. Its
value for half wave rectifier is η = 40.6 %
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4. Explain the construction and working of a full wave rectifier.

Full wave rectifier:

The positive and negative half cycles of the AC input signal
pass through this circuit and hence it is called the full wave
rectifier.

It consists of two P-N junction diodes, a center tapped
transformer, and a load resistor (RL).

The centre (C) is usually taken as the ground or zero voltage
reference point.

Due to the centre tap transformer, the output voltage rectified
by each diode is only one half of the total secondary voltage.
During positive half cycle of input AC:

Terminal M is positive, G at zero potential and N is at negative
potential

Diode D1 is forward biased Diode D2 is reverse biased

D1 conducts and current flows along the path MD1AGC

The voltage appears across RL in the direction G to C
During negative half cycle of input AC:

Terminal M is negative, G is at zero potential and N is at positive potential

Diode D1 is reverse biased Diode D2 is forward biased

D2 conducts and current flows along the path ND2BGC

The voltage appears across RL in the same direction G to C
Input and Output waveform:

Hence in a full wave rectifier both positive and negative half cycles of the input signal pass through
the circuit in the same direction

The output waveform is shown below.

Though both positive and negative half cycles of ac input are rectified, the output is still pulsating in
nature.

The efficiency (η) of full wave rectifier is twice that of a half wave rectifier and is found to be
η = 81.2 %.
5. What is meant by light emitting diode? Explain its working principle with diagram.
Light Emitting Diode (LED):

LED is a p-n junction diode which emits visible or
invisible light when it is forward biased.

Since, electrical energy is converted into light energy; this
process is also called electroluminescence.
Construction:

It consists of a P-layer, N-layer and a substrate.

A transparent window is used to allow light to travel in the
desired direction.

In addition, it has two leads; anode and cathode.

When the P-N junction is forward biased, the conduction
band electrons on N-side and valence band holes on P-side
diffuse across the junction.

When they cross the junction, they become excess minority carriers (electrons in P-side and holes in
N-side).
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These excess minority carriers recombine with oppositely

charged majority carriers respective regions, i.e. the
electrons in conduction band recombine with holes in the
valence band

During recombination process, energy is released in the
form of light (radiative) or heat (non-radiative).

For radiative recombination, a photon of energy hv is
emitted. For non-radiative recombination, energy is
liberated in the form of heat.

The colour of the light is determined by the energy band gap of the material.

Therefore, LEDs are available in a wide range of colours such as
o Blue (SiC)
o Green (AlGaP)
o Red (AsP).

Now a day, LED which emits white light (GaInN) is also available.
6. Explain in detail about the photo diode.
Photo diode:

A P-N junction diode which converts an optical signal into
electric current is known as photodiode.

Thus, the operation of photodiode is exactly opposite to
that of an LED.

Photo diode works in reverse bias. Its circuit symbol is shown below.

The direction of arrows indicates that the light is incident on the photo diode.

The device consists of a P-N junction semiconductor made of photosensitive material kept safely
inside a plastic case

It has a small transparent window that allows light to be incident on the P-N junction.

Photodiodes can generate current when the P-N junction is exposed to light and hence are called as
light sensors.

When a photon of sufficient energy (hv) strikes the depletion region of the diode, some of the
valence band electrons are elevated into conduction band, in turn holes are developed in the valence
band. This creates electron-hole pairs.

The amount of electron - hole pairs generated depends on the intensity of light incident on the P-N
junction.

These electrons and holes are swept across the P-N junction by the electric field created by reverse
voltage before recombination takes place.

Thus, holes move towards the N-side and electrons towards the P-side.

When the external circuit is made, the electrons flow through the external circuit and constitute the
photocurrent.

When the incident light is zero, there exists a reverse current which is negligible.

This reverse current in the absence of any incident light is called dark current and is due to the
thermally generated minority carriers.
7. Explain the working principle of Solar cell. Mention its applications.
Solar cell:

A solar cell, also known as photovoltaic cell, converts
light energy directly into electricity or electric potential
difference by photovoltaic effect.

It is basically a P-N junction which generates emf when
solar radiation falls on the P-N junction.

A solar cell is of two types: P-type and N-type.
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Both types use a combination of P-type and N-type Silicon which together forms the P-N junction of
the solar cell.

The difference is that P-type solar cells use P as the base with an ultra-thin layer of N-type Silicon,
while N-type solar cell uses the opposite combination.

The other side of the P-Silicon is coated with metal which forms the back electrical contact.

On top of the N-type Silicon, metal grid is deposited which acts as the front electrical contact.

The top of the solar cell is coated with anti-reflection coating and toughened glass.

In a solar cell, electron–hole pairs are generated due to the absorption of light near the junction.

Then the charge carriers are separated due to the electric field of the depletion region.

Electrons move towards N–type Silicon and holes move towards P-type Silicon layer.

The electrons reaching the N-side are collected by the front contact and holes reaching P-side are
collected by the back electrical contact.

Thus a potential difference is developed across solar cell.

When an external load is connected to the solar cell, photocurrent flows through the load.

Many solar cells are connected together either in series or in parallel combination to form solar panel
or module.

Many panels are connected with each other to form solar arrays. For high power applications, solar
panels and solar arrays are used.
Applications:
(1) Solar cells are widely used in calculators, watches, toys, portable power supplies, etc.
(2) Solar cells are used in satellites and space application
(3) Solar panels are used to generate electricity.
8. Sketch the static characteristics of a common emitter transistor and bring out the essence of
input and output characteristics.
Static characteristics of NPN transistor in CE mode:

VBE - Base - emitter voltage

VCE − Collector - emitter
voltage

IB - Base current

IC − Collector current

VBB & VCC −Biasing voltages

R1 & R2 − Variable resistors

(1) Input characteristics:

Input Characteristics curves give the relationship between the
base current (IB) and base to emitter voltage (VBE) at constant
collector to emitter voltage (VCE)

The curve looks like the forward characteristics of an ordinary
P-N junction diode.

There exists a threshold voltage or knee voltage (Vk) below
which the base current is very small.

Beyond the knee voltage, the base current increases with the
increase in base-emitter voltage.

It is also noted that the increase in the collector-emitter voltage
decreases the base current. This shifts the curve outward.

This is because the increase in collector-emitter voltage creases the width of the depletion region in
turn, reduces the effective base width and thereby the base current.
J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 249 K.Gomathi M.Sc., B.Ed
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The ratio of the change in base-emitter voltage (∆VBE) to the change in base current (∆IB) at a
constant collector-emitter voltage (VCE) is called the input resistance ( ).
∆ 
= 
∆ 


The input resistance is high for a transistor in common emitter configuration.

(2) Output characteristics:

The output characteristics give relationship between the
variation in collector current (∆IC) with respect to the variation
in collector-emitter voltage (∆VCE) at constant input current (IB)

There are four important regions in the curve
(i) Saturation region
(ii) Cut-off region
(iii) Active region
(iv) Break down region

The ratio of the change in the collector-emitter voltage (∆VCE) to the corresponding change in the
collector current (∆IC) at constant base current (IB) is called output resistance (  ).
∆ 
 = 
∆ 

The output resistance  for transistor in common emitter configuration is very low.
(3) Current transfer characteristics:

This gives the variation of collector current (IC) with changes
in base current (IB) at constant collector-emitter voltage (VCE)

It is seen that a small IC flows even when IB is zero.

This current is called the common emitter leakage current
(ICEO), which is due to the flow of minority charge carriers.

The ratio of the change in collector current (∆IC) to the change in base current (∆IB) at constant
collector-emitter voltage (VCE) is called forward current gain (β).
∆
= 
∆ 

Its value is very high and it generally ranges from 50 to 200.
9. Transistor functions as a switch. Explain.
Transistor as a switch:

The transistor in saturation and cut-off regions
functions like an electronic switch.

That helps to turn ON or OFF a given circuit by a
small control signal.
Presence of dc source at the input (saturation region):

When a high input voltage (Vin = +5 V) is applied,
the base current (IB) increases and in turn increases
the collector current.

The transistor will move into the saturation region (turned ON).

The increase in collector current (IC) increases voltage drop across RC, thereby lowering the output
voltage, close to zero.

The transistor acts like a closed switch and is equivalent to ON condition.

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 250 K.Gomathi M.Sc., B.Ed

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12 - Standard Physics 2, 3, 5 marks
10. Electronics and Communication

Absence of dc source at the input (cut-off region):

A low input voltage (Vin=0V), decreases the base (IB) and in turn decreases the collector current (IC).

The transistor will move into the cut-off region (turned OFF).

The decrease in collector current (IC) decreases the drop across R C, thereby increasing the output
voltage, close to +5 V.

The transistor acts as an open switch which is considered as the OFF condition.

It is manifested that, a high input gives a low output and a low input gives a high output.
Therefore, a transistor can be used as an inverter in computer logic circuitry.
10. Describe the function of a transistor as an amplifier with the neat circuit diagram. Sketch the
input and output wave form.
Transistor as an amplifier:

Amplification is the process of
increasing the signal strength
(increase in the amplitude).

If a large amplification is required,
multistage amplifier is used.

Here, the amplification of an
electrical signal is explained with a
single stage transistor amplifier

Single stage indicates that the circuit
consists of one transistor with the
allied components.

An NPN transistor is connected in
the common emitter configuration.

A load resistance, RC is connected in
series with the collector circuit to
measure the output voltage.

The capacitor C1 allows only the ac signal to pass through.

The emitter bypass capacitor CE provides a low reactance path to the amplified ac signal.

The coupling capacitor CC is used to couple on stage of the amplifier with the next stage while
constructing multistage amplifiers.

VS is the sinusoidal input signal source applied across the base-emitter.

The output is taken across the collector-emitter.

The phase relationship between the AC input and output voltages in a common emitter amplifier is 180°


Collector current is  =   ∵  = 


Applying Kirchhoff ’s voltage law, the collector-emitter voltage is  =    
Working of the amplifier:
(1) During the positive half cycle:

Input signal (Vs) increases the forward voltage across the emitter-base.

As a result, the base current (IB) increases.

Consequently, the collector current (IC) increases β times.

This increases the voltage drop across RC which in turn decreases the collector-emitter voltage (VCE).

Therefore, the input signal in the positive direction produces an amplified signal in negative
direction at the output. Hence, the output signal is reversed by 180°

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 251 K.Gomathi M.Sc., B.Ed

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12 - Standard Physics 2, 3, 5 marks
10. Electronics and Communication

(2) During the negative half cycle:

Input signal (Vs) decreases the forward voltage across the emitter-base.

As a result, base current (IB) decreases and in turn increases the collector current (IC).

The increase in collector current (IC) decreases the potential drop across RC and increases the
collector-emitter voltage (VCE).

Thus, the input signal in the negative direction produces an amplified signal in the positive direction
at the output.

Therefore, 180° phase reversal is observed during the negative half cycle of the input signal
11. Give circuit symbol, logical operation, truth table, and Boolean expression of i) AND gate
ii) OR gate iii) NOT gate iv) NAND gate v) NOR gate and vi) EX-OR gate.
AND Gate
Circuit Symbol Boolean Expression

Let A and B are the inputs and Y be the output,
then
Y = A.B

Logical Operation Truth Table

The output of AND gate is high (1) only when Inputs Output
all the inputs are high (1). A B Y = A.B

The rest of the cases the output is low (0) 0 0 0
0 1 0
1 0 0
1 1 1
OR Gate
Circuit Symbol Boolean Expression

Let A and B are the inputs and Y be the output,
then
Y=A+B
Logical Operation Truth Table

The output of OR gate is high (1) when either Inputs Output
of the inputs or both are high (1) A B Y=A+B

The rest of the cases the output is low (0) 0 0 0
0 1 1
1 0 1
1 1 1
NOT Gate
Circuit Symbol Boolean Expression

If A be the input and Y be the output, then
=!

Logical Operation Truth Table

The output is the complement of the input. It is
Input Output
= !
represented with an overbar. It is also called as
inverter. A
The output Y is high (1), when input is low (0) 0 1
and vice versa. 1 0

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12 - Standard Physics 2, 3, 5 marks
10. Electronics and Communication

NAND Gate
Circuit Symbol Boolean Expression

Let A and B are the inputs and Y be the output,
then
 = $$$$$$
.#

Logical Operation Truth Table

The output Y equals the complement of AND
Inputs Output Output
$
operation.
=%

The circuit is an AND gate followed by a NOT A B %= .# $$$$$$
gate. Therefore, it is summarized as NAND.  = .#

The output is at low (0) only when all the 0 0 0 1
inputs are high (1). 0 1 0 1
The rest of the cases, the output is high (1) 1 0 0 1
1 1 1 0

NOR Gate
Circuit Symbol Boolean Expression

Let A and B are the inputs and Y be the output,
then
 = $$$$$$$$
+#
Logical Operation Truth Table

The output Y equals the complement of OR
operation Inputs Output Output
=% $

The circuit is an OR gate followed by a NOT %= +#
 = $$$$$$$$
A B
gate and is summarized as NOR +#

The output is high (1) when all the inputs are 0 0 0 1
low (0). 0 1 1 0

The rest of the cases, the output is low (0) 1 0 1 0
1 1 1 0

EX-OR Gate
Circuit Symbol Boolean Expression

Let A and B are the inputs and Y be the output,
then
! + !. #
 = .#
 = ⨁#
Logical Operation Truth Table

The output Y is high (1) only when either of
Inputs Output
the two inputs is high (1).
A B = ⨁#

In the case of an Ex-OR gate with more than
two inputs, the output will be high (1) when 0 0 0
odd number of inputs are high (1) 0 1 1
1 0 1
1 1 0

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 253 K.Gomathi M.Sc., B.Ed

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12 - Standard Physics 2, 3, 5 marks
10. Electronics and Communication

12. State and prove De Morgan’s First and Second theorems.

De Morgan’s First Theorem:

The complement of the sum of two logical inputs is
equal to the product of its complements.
$$$$$$$$
+ # = ! .# !
Proof:

The Boolean equation for NOR gate is ) = $$$$$$$$+#

The Boolean equation for a bubbled AND gate is
) = ! .# !

From the above truth table, $$$$$$$$
+ # = ! .#!

Thus De Morgan’s First Theorem is proved.

It also says that a NOR gate is equal to a bubbled
AND gate. The corresponding logic circuit diagram
De Morgan’s Second Theorem:

The complement of the products of two logical inputs
is equal to the sum of its complements.
$$$$$$
.# = ! + # !
Proof:

The Boolean equation for NAND gate is ) = $$$$$$ .#

The Boolean equation for a bubbled OR gate is
* = !+# !

From the above truth table, $$$$$$.# = ! + #!

Thus De Morgan’s second Theorem is proved.

It also says that a NAND gate is equal to a bubbled
OR gate. The corresponding logic circuit diagram
13. What is called modulation? Explain the types of modulation with help of necessary diagrams.
Modulation :

For long distance transmission, the low frequency baseband signal (input signal) is superimposed
onto a high frequency radio signal by a process called modulation.

In the modulation process, a very high frequency signal called carrier signal (radio signal) is used to
carry the baseband signal.
Types of modulation :
(1) Amplitude modulation (AM)
(2) Frequency modulation (FM)
(3) Phase modulation (PM)
1. Amplitude modulation (AM) :

If the amplitude of the carrier signal is modified
according to the instantaneous amplitude of the
baseband signal, then it is called amplitude modulation.

Here the frequency and the phase of the carrier signal
remain constant.

We can see clearly that the carrier wave is modified in
proportion to the amplitude of the baseband signal.

Amplitude modulation is used in radio and TV
broadcasting.
Advantages of AM :

Easy transmission and reception

lesser bandwidth requirements

Low cost

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 254 K.Gomathi M.Sc., B.Ed

Govt. Boys Hr. Sec. School, Vennandur, Rasipuram, Namakkal District
12 - Standard Physics 2, 3, 5 marks
10. Electronics and Communication

Limitations of AM :

Noise level is high

Low efficiency

Small operating range
2. Frequency modulation (FM) :

If the frequency of the carrier signal is modified
according to the instantaneous amplitude of the
baseband signal, then it is called frequency modulation.

Here the amplitude and the phase of the carrier signal
remain constant.

When the amplitude of the baseband signal is zero, the
frequency of the modulated signal is the same as the
carrier signal.

The frequency of the modulated wave increases when
the amplitude of the baseband signal increases in the
positive direction (A, C).

The increase in amplitude in the negative half cycle (B,
D) reduces the frequency of the modulated wave

When the frequency of the baseband signal is zero (no
input signal), there is no change in the frequency of the
carrier wave.

It is at its normal frequency and is called as centre
frequency or resting frequency.

Practically 75 kHz is the allotted frequency of the FM transmitter.
Advantages of FM :

Large decrease in noise. This leads to an increase in signal-noise ratio.

The operating range is quite large.

The transmission efficiency is very high as all the transmitted power is useful.

FM bandwidth covers the entire frequency range which humans can hear. Due to this, FM radio has
better quality compared to AM radio.
Limitations of FM :

FM requires a much wider channel.

FM transmitters and receivers are more complex and costly.

In FM reception, less area is covered compared to AM.
3. Phase modulation (PM) :

In phase modulation, the instantaneous amplitude of the baseband signal modifies the phase of the
carrier signal keeping its amplitude and frequency constant.

This modulation is used to generate frequency modulated signals.

It is similar to frequency modulation except that the phase of the carrier is varied instead of varying
frequency.

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 255 K.Gomathi M.Sc., B.Ed

Govt. Boys Hr. Sec. School, Vennandur, Rasipuram, Namakkal District
12 - Standard Physics 2, 3, 5 marks
10. Electronics and Communication

14. Elaborate on the basic elements of communication system with the necessary block diagram.
Communication system :

Electronic communication is nothing but the transmission of sound, text, pictures, or data through a
medium.
Basic elements of communication system :
1. Input transducer :

A transducer is a device that converts variations in a physical quantity (pressure, temperature, sound)
into an equivalent electrical signal or vice versa.

In communication system, the transducer converts the information which is in the form of sound,
music, pictures or computer data into corresponding electrical signals.

The electrical equivalent of the original information is called the baseband signal. (e.g.) microphone
2. Transmitter :

It feeds the electrical signal from the
transducer to the communication
channel.

The transmitter is located at the
broadcasting station.

Transmitter consists,
o Amplifier :

The transducer output is very weak and is amplified by the amplifier.
o Oscillator :

It generates high-frequency carrier wave (a sinusoidal wave) for long distance transmission into
space.
o Modulator :

It superimposes the baseband signal onto the carrier signal and generates the modulated signal.
o Power amplifier :

It increases the power level of the electrical signal in order to cover a large distance.
3. Transmitting antenna :

It radiates the radio signal into space in all directions.

It travels in the form of electromagnetic waves with the velocity of light (3 × 108 m s–1)
4. Communication channel :

Communication channel is used to carry the electrical signal from transmitter to receiver with less
noise or distortion.

The communication medium is basically of two types:
o wireline communication
o wireless communication.
5. Receiver :

The signals that are transmitted
through communication medium are
received with help of a receiving
antenna and are fed into the receiver.

The receiver consists of electronic circuits like demodulator, amplifier, detector etc
o Demodulator:

The demodulator extracts the baseband signal from the carrier signal.
o Amplifier:

Then the baseband signal is detected and amplified using amplifiers. Finally, it is fed
to the output transducer.
6. Output transducer :

It converts the electrical signal back to its original form such as sound, music, pictures or data.

(e.g.) loudspeakers, picture tubes, computer monitor, etc.,
J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 256 K.Gomathi M.Sc., B.Ed
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12 - Standard Physics 2, 3, 5 marks
10. Electronics and Communication

15. Explain the three modes of propagation of electromagnetic waves through space.
Modes of propagation of electromagnetic waves :

The electromagnetic wave transmitted by :
a. Ground wave propagation (or) surface wave propagation
(2 kHz to 2 MHz)
b. Sky wave propagation (or) ionospheric propagation
(3 MHz to 30 MHz)
c. Space wave propagation
(30 MHz to 400 GHz)
Ground wave propagation :

If the electromagnetic waves transmitted by the transmitter
glide over the surface of the earth to reach the receiver, then
the propagation is called ground wave propagation.

The corresponding waves are called ground waves or surface
waves.

Both transmitting and receiving antennas must be close to the
earth.

It is mainly used in local broadcasting, radio navigation, for
ship-to-ship, ship-to-shore communication and mobile
communication.
Sky wave propagation :

The mode of propagation in which the electromagnetic waves radiated from an antenna, directed
upwards at large angles, gets reflected by the ionosphere back to Earth is called sky wave
propagation or ionospheric propagation.

The corresponding waves are called sky waves.

Ionosphere acts as a reflecting surface.

It is at a distance of approximately 50 km and spreads up to 400 km above the Earth's surface.

Due to the absorption of ultraviolet rays, cosmic ray, and other high energy radiations like α, β rays
from sun, the air molecules in the ionosphere get ionized.

This produces charged ions and these ions provide a reflecting medium for the reflection of radio
waves or communication waves back to Earth within the permitted frequency range.

The phenomenon of bending the radio waves back to Earth is nothing but the total internal
reflection.

When the angle of incidence at the ionosphere is large, the sky wave returns to the ground at a long
distance from the transmitter.

As this angle is reduced, the wave returns closer and closer to the transmitter.

If the angle of incidence is reduced further, the radio waves penetrate through the ionosphere.

For a particular angle of incidence, the point of reception (B) is at the minimum distance from
transmitter.

The shortest distance between the transmitter and the point of reception of the sky wave along the
surface is called as the skip distance.

The ground waves get attenuated as they move away from the transmitter.

At a particular point (A), there is no reception ground wave.

The zone (in between A and B) where there is no reception of electromagnetic waves neither ground
nor sky is known as skip zone or skip area.
J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 257 K.Gomathi M.Sc., B.Ed
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12 - Standard Physics 2, 3, 5 marks
10. Electronics and Communication

Space wave propagation :

The process of sending and receiving information signal through space is called space wave
communication

The electromagnetic waves of very high frequencies above 30 MHz are called as space waves.

These waves travel in a straight line from the transmitter to the receiver. Hence, it is used for a line
of sight communication (LOS).

The communication systems like television broadcast, satellite communication, and RADAR are
based on space wave propagation.

The range or distance (d) of coverage propagation depends on the height (h) of the antenna given by
the equation, + = √2ℎ where, R → Radius of earth (6400 km)
16. Fiber optic communication is gaining popularity among the various transmission media-Justify.
Fiber optic communication :

The method of transmitting information from one place to another in terms of light pulses through an
optical fiber is called fiber optic communication.

It is in the process of replacing wire transmission in communication systems.

Light has very high frequency (400THz –790 THz) than microwave radio systems.

The fibers are made up of silica glass or silicon dioxide which is highly abundant on Earth.

Now it has been replaced with materials such as chalcogenide glasses, fluoroaluminate crystalline
materials because they provide larger infrared wavelength and better transmission capability.

As fibers are not electrically conductive, it is preferred in places where multiple channels are to be
laid and isolation is required from electrical and electromagnetic interference.
Applications :

Optical fiber system has a number of applications namely, international communication, inter-city
communication, data links, plant and traffic control and defense applications.
Merits :

Fiber cables are very thin and weigh lesser than copper cables.

This system has much larger band width. That means that its information carrying capacity is larger.

Fiber optic system is immune to electrical interferences.

Fiber optic cables are cheaper than copper cables.
Demerits :

Fiber optic cables are more fragile when compared to copper wires.

It is an expensive technology.
Importance :

Fiber optic cables provide the fastest transmission rate compared to any other form of transmission.

It can provide data speed of 1 Gbps for homes and business.

Multimode fibers operate at the speed of 10 Mbps.

Recent developments in optical communication provide the data speed at the rate of 25 Gbps
17. Give the advantages and limitations of frequency modulation (FM)
Advantages of FM :

Large decrease in noise. This leads to an increase in signal-noise ratio.

The operating range is quite large.

The transmission efficiency is very high as all the transmitted power is useful.

FM bandwidth covers the entire frequency range which humans can hear. Due to this, FM radio has
better quality compared to AM radio.
Limitations of FM :

FM requires a much wider channel.

FM transmitters and receivers are more complex and costly.

In FM reception, less area is covered compared to AM.

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 258 K.Gomathi M.Sc., B.Ed

Govt. Boys Hr. Sec. School, Vennandur, Rasipuram, Namakkal District
12 - Standard Physics 2, 3, 5 marks
10. Electronics and Communication

18. What is meant by satellite communication? Give its applications.

Satellite communication :

The satellite communication is a mode of
communication of signal between transmitter and
receiver via satellite.

The message signal from the Earth station is
transmitted to the satellite on board via an uplink
(frequency band 6 GHz), amplified by a transponder
and then retransmitted to another earth station via a
downlink (frequency band 4 GHz)

The high-frequency radio wave signals travel in a straight line (line of sight) may come across tall
buildings or mountains or even encounter the curvature of the earth.

A communication satellite relays and amplifies such radio signals via transponder to reach distant
and far off places using uplinks and downlinks.

It is also called as a radio repeater in sky.
Applications :
1. Weather Satellites:

They are used to monitor the weather and climate of Earth.

By measuring cloud mass, these satellite enable us to predict rain and dangerous storms like
hurricanes, cyclones etc.
2. Communication satellites:

They are used to transmit television, radio, internet signals etc. Multiple satellites are used for long
distances.
3. Navigation satellites:

These are employed to determine the geographic location of ships, aircrafts or any other object.
19. Explain the function of RADAR. Give its applications.
RADAR :

RADAR basically stands for RAdio Detection And Ranging System.

It is one of the important applications of communication systems and is mainly used to sense, detect,
and locate distant objects like aircraft, ships, spacecraft, etc.

The angle, range, or velocity of the objects that are invisible to the human eye can be determined.

Radar uses electromagnetic waves for communication.

The electromagnetic signal is initially radiated into space by an antenna in all directions.

When this signal strikes the targeted object, it gets reflected or reradiated in many directions.

This reflected (echo) signal is received by radar antenna which in turn is delivered to the receiver.

Then, it is processed and amplified to determine the geographical statistics of the object.

The range is determined by calculating the time taken by the signal to travel from RADAR to the
target and back.
Applications :

In military, it is used for locating and detecting the targets.

It is used in navigation systems such as ship born surface search, air search and weapons guidance
systems.

To measure precipitation rate and wind speed in meteorological observations, Radars are used.

It is employed to locate and rescue people in emergency situations.

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 259 K.Gomathi M.Sc., B.Ed

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 12 - Standard Physics 2, 3, 5 marks
11. Recent Developments in Physics
,a,

6. Write a note on black holes.

Black holes :

Black holes are end stage of stars which are highly dense massive object.

Its mass ranges 20 times mass of the sun to 1 million times mass of the sun.

It has very strong gravitational force such that no particle or even light can escape from it.

The existence of black hole is studied when the stars orbiting the black hole behave differently from
the other stars.

Every galaxy has black hole at its centre.

Sagittarius A* is the black hole at the centre of the Milky Way galaxy.
7. What are sub atomic particles?

Sub atomic particles are smaller than an atom.

It consist some particle which is building block of atoms.

Some sub atomic particles are larger than Hydrogen atom.

There two types of sub atomic particles
o Fundamental particles
o Compound particles
SHORT ANSWER QUESTIONS (CONCEPTUAL)
8. Give the interdisciplinary nature of nano technology.

Nano science and technology is the interdisciplinary area covering its applications in various fields.
They are,
1. Physics
2. Chemistry
3. Electrical & Mechanical Engineering
4. Material science
5. Molecular Biology
6. Applied Mathematics & Computer science
9. What is robotics?

Robotics is an integrated study of mechanical, electronic engineering, computer engineering and
science.
Robot is a mechanical device designed with electronic circuitry and programmed to perform a
specific task.
10. Explain how nano structures are made in the laboratory?
Nano in laboratories :

The nano structures made in the laboratory mimic some of the nature’s amazing nano structures.

There are two ways of preparing the Nanomaterials. They are.
1. Top - Down approach 2. Bottom - Up approach
1. Top - Down approach :

Nano materials are synthesized by breaking down bulk solids in to nano sizes. (e.g.) Ball milling,
sol-gel, lithography
2. Bottom - up approach :

Nano materials are synthesized by assembling the atoms or molecules together. Selectively atoms
are added to create structures. (e.g.) plasma etching and chemical vapour deposition
11. List the applications of Nano technology.
Applications of Nano technology.

Energy storage
Biomedical and drug delivery

Defense and security
Agriculture and food

Metallurgy and materials
Cosmetics and paints

Electronics
Bio-technology

Optical engineering and communication
Textiles

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 266 K.Gomathi M.Sc., B.Ed

Govt. Boys Hr. Sec. School, Vennandur, Rasipuram, Namakkal District
 12 - Standard Physics 2, 3, 5 marks
11. Recent Developments in Physics
,a,

12. What are the components of robotics?

The robotic system mainly consists of
1. Sensors
2. Power supplies
3. Control systems
4. Manipulators
5. Necessary software
13. Give the types of robots.
1. Human robot :

Certain robots are made to resemble humans in appearance and replicate the human activities like
walking, lifting and sensing etc
2. Industrial robots :

Six main types of industrial robots are Cartesian, SCARA, Cylindrical, Delta, Polar and vertically
articulated.

They are ideal for Arc welding, Spot welding, Material handling, machine tending and other
applications.
14. What is artificial intelligence? What is its work?
Artificial Intelligence:

The aim of artificial intelligence is to bring in human like behaviour in robots.
Artificial Intelligence works on:
1. Face recognition
2. Providing response to player’s actions is computer game
3. Taking decisions based on previous actions
4. To regulate the traffic by analyzing the density of traffic on roads
5. Translate words from one language to another
15. Give the applications of robot in various fields.
Applications of robot :

Weaponry, packing, Lawn mowing, cutting, under water, agriculture, pool cleaning

Welding, cutting, assembling, litter robot, transport.

Vacuum cleaners, hospitals, surgery, laboratory

Exploring stars, planets etc., investigation of the mineralogy of the rocks and soils on Mars, analysis
of elements found in rocks and soils
16. Write a note on nano robots.
Nano robots :

The size of the nano robots is reduced to microscopic level to perform a task in very small spaces.

In future nano robots are used in the medical fields.

Nano robots in blood stream to perform small surgical procedures, to fight against bacteria, repairing
individual cell in the body.

It can travel into the body and once after the job is performed it can find its way out.
17. What is particle physics? Write down its recent development.
Particle physics :

The study of the theory of fundamental particles of nature is called particle physics.
Particle physics development :

Initially it was thought that atom is the fundamental entity of matter. But in 1930, it was established
that atoms are made up of electrons, protons and neutrons

In 1960, it was discovered that protons and neutrons were made up of quarks.

Later it was found that quarks interact through gluons.

Recently in 2013, famous Higgs particles also known as God particles were discovered which gives
mass to many particles like protons, neutrons etc .,

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 267 K.Gomathi M.Sc., B.Ed

Govt. Boys Hr. Sec. School, Vennandur, Rasipuram, Namakkal District
 12 - Standard Physics 2, 3, 5 marks
11. Recent Developments in Physics
,a,

18. Write a note on Cosmology.

Cosmology:

Cosmology is the branch that involves the origin and evolution of the universe.

It deals with the formation of stars, galaxy etc.
19. What are called gravitational waves?
Gravitational Waves:

The disturbances in the curvature of space-time are called gravitational waves. Its travels with speed of light.

Any accelerated charge emits electromagnetic waves. Similarly any accelerated mass emits
gravitational waves.

But the gravitational waves are very weak even for masses like earth.

The strongest sources of gravitational waves are black holes.

The recent discoveries of gravitational waves are emitted by two black holes when they merge to a
single black hole.

In 1915, Albert Einstein theoretically proposed the existence of gravitational waves. After 100 years,
it is experimentally proved that his predictions are correct.
LONG ANSWER QUESTIONS (5 Marks)
1. Explain Nano structure in nature with examples.
Nano in nature :
(1) Single strand DNA :

It is the basic building block of all living things.

It is about 3 nm wide
(2) Morpho butterfly :

The scales of the wings of this butterfly contain nano structures.

When light wave interact with this giving the wings brilliant metallic blue and green hues.
(3) Peacock feathers :

They get their iridescent coloration from light interacting with 2 dimensional photonic crystal
structures just tens of nanometers thick

Similar nano structures are made in lab to glow in different colors
(4) Parrot fish :

It crunches up coral all day.

The source of powerful bite is the interwoven fiber nanostructure.

Crystals of a mineral called fluorapatite are woven together in a chain mail-like arrangement. This
structure gives parrot fish teeth incredible durability.

It provides a blue print for creating ultra-durable synthetic materials that could be useful for
mechanical components in electronics and in other devices that undergo repetitive movement,
abrasion and contact stress
(5) Lotus Leaf surface :

Scanning electron micrograph (SEM) gives the nano structures on the surface of a leaf from a lotus plant.

This is the reason for self cleaning process on lotus leaf.
2. Comment on the recent advancement in medical diagnosis and therapy.
1. Virtual reality:

Medical virtual reality is effectively used to stop the brain from processing pain and cure soreness in
the hospitalized patients.

It helps in the treatment of Autism, Memory loss, and Mental illness.
2. Precision medicine:

Precision medicine is an emerging approach for disease treatment and prevention that takes into
account individual variability in genes, environment, and lifestyle for each person.
3. Health wearables:

A health wearable is a device used for tracking a wearer's vital signs or health and fitness related
data, location, etc.
J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 268 K.Gomathi M.Sc., B.Ed
Govt. Boys Hr. Sec. School, Vennandur, Rasipuram, Namakkal District
 12 - Standard Physics 2, 3, 5 marks
11. Recent Developments in Physics
,a,

Medical wearables with artificial intelligence and big data provide an added value to healthcare with
a focus on diagnosis, treatment, patient monitoring and prevention.
4. Artificial organs:

An artificial organ is an engineered device or tissue that is implanted or integrated into a human.

It is possible to interface it with living tissue or to replace a natural organ. It duplicates or augments
a specific function or functions of human organs so that the patient may return to a normal life as
soon as possible.
5. 3D printing:

Advanced 3D printer systems and materials assist physicians in a range of operations in the medical
field from audiology, dentistry, orthopedics and other applications.
6. Wireless brain sensors:

Wireless brain sensors monitor intracranial pressure and temperature and then are absorbed by the
body. Hence there is no need for surgery to remove these devices.
7. Robotic surgery:

Robotic surgery is a type of surgical procedure that is done using robotic systems.

Robotically-assisted surgery helps to overcome the limitations of pre-existing minimally-invasive
surgical procedures and to enhance the capabilities of surgeons performing open surgery.
8. Smart inhalers:

Inhalers are the main treatment option for asthma. Smart inhalers are designed with health systems
and patients in mind so that they can offer maximum benefit.

Smart inhalers use Bluetooth technology detect inhaler use, remind patients when to take their
medication and gather data to help guide care.
3. Discuss the functions of key components in Robots?
Functions of key components of Robots :

Most robots are composed of 3 main parts:
1. Controller
2. Mechanical parts
3. Sensors
Controller :

It is also known as the "brain" which is run by a computer program.

It gives commands for the moving parts to perform the job.
Mechanical parts :

It consist motors, pistons, grippers, wheels gears that make the robot move, grab, turn, and lift.
Sensors :

It tells the robot about its surroundings. It helps to determine the sizes and shapes of the objects
around, distance between the objects, and directions as well.
4. What are the possible harmful effects of usage of Nanoparticles? Why?
Possible harmful effects of nano particles :

The major concern here is that the nanoparticles have the dimensions same as that of the biological
molecules such as proteins. They may easily get absorbed on to the surface of living organisms and
they might enter the tissues and fluids of the body.

The adsorbing nature depends on the surface of the nanoparticle. Indeed, it is possible to deliver a
drug directly to a specific cell in the body by designing the surface of a nanoparticle so that i adsorbs
specifically on to the surface of the target cell.

The interaction with living systems is also affected by the dimensions of the nanoparticles.

Nanoparticles can also cross cell membranes. It is also possible for the inhaled nanoparticles to reach
the blood, to reach other sites such as the liver, heart or blood cells.

Researchers are trying to understand the response of living organisms to the presence of
nanoparticles of varying size, shape, chemical composition and surface characteristics.

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 269 K.Gomathi M.Sc., B.Ed

Govt. Boys Hr. Sec. School, Vennandur, Rasipuram, Namakkal District
 12 - Standard Physics 2, 3, 5 marks
11. Recent Developments in Physics
,a,

5. Discuss the applications of Nanomaterials in various fields.

Automotive industry: Construction:

Lightweight construction
Construction materials

Painting (fillers, base coat, clear coat)
Thermal insulation

Catalysts
Flame retardants

Tires (fillers)
Surface-functionalised building materials for

Sensors wood, floors, stone, facades, tiles, roof tiles,

Coatings for windscreen and car bodies etc.
Chemical industry:
Facade coatings

Fillers for paint systems
Groove mortar

Coating systems based on nano composites Medicine:

Impregnation of papers
Drug delivery systems

Switchable adhesives
Active agents

Magnetic fluids
Contrast medium
Engineering:
Medical rapid tests

Wear protection for tools and machines
Prostheses and implants

Lubricant-free bearings
Antimicrobial agents and coatings
Electronic industry:
Agents in cancer therapy

Data memory Food and drinks:

Displays
Package materials

Laser diodes
Storage life sensors

Glass fibres
Additives

Optical switches
Clarification of fruit juices

Filters (IR-blocking) Household:

Conductive, antistatic coatings
Ceramic coatings for irons
Energy:
Odors catalyst

Fuel cells
Cleaner for glass,

Solar cells
Ceramic, floor, windows

Batteries Sports/ outdoor:

Capacitors
Ski wax
Cosmetics:
Antifogging of glasses/goggles

Sun protection
Antifouling coatings for ships/boats

Lipsticks
Reinforced tennis rackets and balls

Skin creams Textile/fabrics/non-woven:

Tooth paste
Surface-processed textiles

Smart clothes
6. Explain the various components of robotics.
Power conversion unit:

Robots are powered by batteries, solar power, and hydraulics.
Actuators:

Actuator converts energy into movement. The majority of the actuators produce rotational or linear
motion.
Electric motors:

They are used to actuate the parts of the robots like wheels, arms, fingers, legs, sensors, camera,
weapon systems etc.

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 270 K.Gomathi M.Sc., B.Ed

Govt. Boys Hr. Sec. School, Vennandur, Rasipuram, Namakkal District
 12 - Standard Physics 2, 3, 5 marks
11. Recent Developments in Physics
,a,

Different types of electric motors are used. The most often used ones are AC motor, Brushed DC
motor, Brushless DC motor, Geared DC motor, etc.
Pneumatic Air Muscles:

They are devices that can contract and expand when air is pumped inside.

It can replicate the function of a human muscle. They contract almost 40% when the air is sucked
inside them.
Muscle wires:

They are thin strands of wire made of shape memory alloys. ey can contract by 5% when electric
current is passed through them.
Piezo Motors and Ultrasonic Motors:

Basically, we use it for industrial robots.
Sensors:

Generally used in task environments as it provides information of real-time knowledge.
Robot locomotion:

Robot locomotion provides the types of movements to a robot.

The different types are
o Legged
o Wheeled
o Combination of Legged and Wheeled Locomotion
o Tracked slip/skid

All The Best

J. Sisubaladhanasekar M.Sc., M.Phil, B.Ed
K.Gomathi M.Sc., B.Ed
PG Assistants in Physics
Govt. Boys Hr. Sec. School
Vennandur, Rasipuram Tk
Namakkal District
Cell: 9488575180

J.Sisubaladhanasekar M.Sc., M.Phil, B.Ed 271 K.Gomathi M.Sc., B.Ed

Govt. Boys Hr. Sec. School, Vennandur, Rasipuram, Namakkal District