ATOMS
One mark questions
1) How do we define angle of scattering in α-particle scattering experiment?
2) What was Balmer’s contribution for the study of hydrogen spectrum?
3) Define the term ‘impact parameter in α-particle scattering experiment.
4) Name the series of hydrogen spectrum which has least wavelength.
5) Name the series of hydrogen spectrum that lies in UV region.
6) To which part of the electromagnetic spectrum does Lyman series belong?
7) Name the series of hydrogen spectrum which lies in the visible region.
8) To which part of the electromagnetic spectrum does Balmer series belong?
9) To which part of the electromagnetic spectrum does Paschen series belong?
10) An electron transits from 5th orbit to 3rd orbit in hydrogen atom, Name the region of the spectral line to which it
belongs.
11) What is meant by the series limit of a spectral series?
12) Which force provides the centripetal force required for the electron to go round the nucleus in uniform
circular motion in Bohr atom?
13) What does a stationary orbit mean according to Bohr in his atom model?
14) Does an electron revolving round a nucleus in a Bohr atom radiate energy?
15) Write Bohr's quantisation rule.
16) When does an atom radiate energy according to Bohr's theory?
17) What information do we get by the study of line spectrum?
18) How is the wave number of a spectral line related to its wavelength?
19) What is the value of Rydberg's constant?
20) What is meant by the energy level diagram for an atom?
21) In Bohr's atomic model which energy level corresponds to the minimum energy?
22) What is ionization energy?
23) What is excitation energy?
Two mark questions
1. Who proposed plum pudding model for atom? Describe the arrangement of constituents of atom in it.
2. Who discovered electron? And which experiment has led to its discovery?
3. Who proposed planetary model of atom? Explain how the constituents of atom are arranged according to this model.
4. Mention the two draw backs of Rutherford’s atom model.
5. Show graphically the variation of number of α-particle scattered with the scattering angle for a given energy of α-
particle.
6. Draw a schematic diagram of Geiger-Marsden α-particle scattering experiment.
7. When the impact parameter is said to be (a) maximum? & (b) minimum?
Calculate the wavelength of 𝐻𝛼 -line using Balmer formula. Given Rydberg constant= 1.097X107m-1.
8. Give the names of first two members of the Balmer series.
9.
10. Write Balmer formula for the wavelengths of spectral series of hydrogen atom and explain the terms.
11. How do we get series limit using Balmer formula? Write the value of the shortest wavelength in the Balmer series.
12. Write the empirical formula for wave number of first two spectral series.
13. Write Bohr's frequency condition and explain the terms.
14. What is ‘Bohr radius’? Write its formula.
15. Write the expression for Rydberg's constant and explain the terms.
16. Write the formula for the energy of electron in nth Bohr orbit of hydrogen atom in electron volt and write
the value for the third orbit.
Three mark questions
1. What are the experimental observations of Geiger-Marsden's scattering experiment?
2. Explain briefly the conclusions of Rutherford α-particle scattering experiment.
3. Define impact parameter in α-scattering experiment. How does the scattering angle depends on impact
parameter and what is the conclusion drawn by Rutherford by analyzing this?
4. State the basic assumptions of the Rutherford nuclear model of an atom.
5. Name the first three spectral series of hydrogen atom.
6. State the postulates of Bohr's theory of hydrogen atom.
7. Sketch the energy level diagram of hydrogen atom.
8. Obtain the Bohr's quantisation condition on the basis of de-Broglie's theory (wave picture of an electron).
9. Mention any three limitations of Bohr's atom model.
Five mark questions
1. Explain with a schematic diagram, Geiger-Marsden experiment of α-particle scattering.
2. Derive the expression for the total energy of an electron in a hydrogen atom on the basis of Rutherford's atom model.
3. Explain spectral series of hydrogen atom. (U)
4. Derive the expression for the radius of 𝑛𝑡ℎ stationary orbit of hydrogen atom using Bohr’s
postulates.
5. Derive the expression for the total energy of an electron in nth stationary orbit of hydrogenatom by assuming the
expression for orbit radius.
6. Derive the expression for the frequency of radiation in hydrogen spectrum assuming the expression for energy of
electron in a stationary orbit.
Numerical problems.
1. The wavelength of the first member of the Balmer series in the hydrogen spectrum is 656.3nm. Calculate the wavelength
of the first member of the Lyman series in the same spectrum. [121.54 nm]
2. The energy of an excited hydrogen atom is -3.4eV. Calculate the angular momentum of the electron according to Bohr’s
theory. [2.11X10-34Js]
3. A doubly ionized lithium atom has atomic number 3. Find the wavelength of the radiation required to excite the electron
in Li+2 from the first to the third Bohr orbit. Assume that the ionization energy is 13.6eV. [113.74 A0 ]
4. A stationary He+ emitted a photon corresponding to the first line of Lyman series. This photon liberated a photo electron
from a stationary hydrogen atom in the ground state. Find the velocity of the photo electron. [3.1X106ms-1 ]
5. A hydrogen atom rises from its n=1 state to the n=4 state by absorbing energy. If the potential energy of the atom in n=1
state is -13.6 eV, calculate the potential energy in n=4 state and energy absorbed by the atom in the transition from n=1 to
n=4 state.
6. Calculate the de Broglie wavelength of a neutron moving with a kinetic energy 150 eV, and an electron accelerated by a
voltage of 50KV. given mass of the neutron = 1.675X10-27Kg, and that of electron = 9.1X10-31 Kg. (A) [2.3X10-12 m, 5.5X10-
12
m]
NUCLEI
One mark questions
1) Define atomic mass unit (amu).
2) Write the value of 1 atomic mass unit in kilogram.
3) Name the instrument used to measure the atomic masses.
4) How is the radius of the nucleus of an atom related to its mass number?
5) What is the radius of a nucleus of mass number 216?
6) What is the order of the magnitude of nuclear density?
7) How does the nuclear density depend on the size of the nucleus?
8) Is the nuclear density same for all the elements?
9) Give an example for mass-energy conversion.
10) Give an example showing the conversion of energy into mass.
11) What happens when an electron and a positron collide?
12) What is the energy equivalent to 1amu?
13) Who discovered neutron?
14) Do free neutrons are stable?
15) Define mass number of nucleus?
16) How many isotopes gold has?
17) What are isobars?
18) What are isotones?
19) What is nuclear mass defect?
20) Write the expression for mass defect in terms of masses of their nucleons.
21) What is nuclear binding energy?
22) Give the relation between binding energy and mass defect.
23) What happens to the loss of mass involved in the formation of a nucleus?
24) Mention the significance of binding energy per nucleon of a nucleus.
25) What is binding energy curve?
26) What are nuclear forces?
27) Why nuclear forces are strongest of all the forces in nature?
28) Why nuclear forces are called short range forces?
29) Why nuclear forces are called exchange forces?
30) Nuclear forces are non-central forces Explain?
31) Nuclear forces are saturated forces why?
32) Which property of nuclear forces is responsible for constancy of binding energy per nucleon?
33) Name the phenomenon by which energy is produced in star.
34) Why nuclear fusion reactions are called thermo nuclear reactions?
35) Write any one equation representing nuclear fusion reaction.
36) Why nuclear fusion reaction is not possible in the laboratory?
37) What is radioactivity?
38) Who discovered the phenomenon of radio activity?
39) How many types of radioactive decay occur in nature?
40) What is the cause for the radioactivity in lighter nuclei?
41) How does the number of radioactive atoms vary with time?
42) Show graphically the variation or number of radioactive atoms in the sample with time.
43) Define activity of radioactive substance.
44) Mention the SI unit of activity.
45) Define becquerel.
46) Mention the practical unit of activity.
47) Define curie.
48) Write the equivalence between curie and becquerel.
49) How does the half-life of a radioactive sample depend on its decay constant?
50) Define mean life of a radioactive substance.
51) Write the relation between mean life and half-life of a radioactive nuclide.
52) What is disintegration energy or Q-value of a nuclear reaction?
53) In which type of β-decay antineutrino is emitted?
54) Which is the particle emitted along with electron, when a neutron is converted into a proton
in a nucleus?
55) In which type of β-decay, the particle neutrino is emitted?
56) In the following nuclear reaction identify the particle X.
p n e X
57) Two nuclei have mass numbers in the ratio 8:125. What is the ratio of their nuclear radii?
58) What is nuclear fission?
59) What is the principle of nuclear reactor?
60) Define’ multiplication factor’ in a nuclear reactor?
61) For what value of ‘k’ the multiplication factor the operation of the reactor is said to be critical? (K)
62) Which moderators are commonly used in nuclear reactors?
63) Mention the disaster which occurred due to increase of multiplication factor in a nuclear reactor.
64) How nuclear reaction rate is controlled in a nuclear reactor?
65) What is the function of control rods in a nuclear reactor?
66) What is nuclear fusion?
67) What is the estimated age of the sun based on nuclear reactions?
Two mark questions
1. What are isotopes? Give an example of it.
2. Name the isotopes of hydrogen and write their masses.
3. What are isobars? Give an example.
4. What are isotones? Mention an example of it.
5. Do free neutrons are stable in nature? Justify your answer.
6. What is meant by binding energy per nucleon? Explain.
7. Nuclear forces are strongest forces in nature why?
8. What are neutrinos? In which process they are obtained?
9. Write any two characteristics of neutrinos.
10. Where does the decay of proton to neutron take place? And why?
11. State and explain radioactive decay law.
12. Mention any two types of radioactive decay in nature.
13. What is γ-decay? When does this occur?
14. What is the change in atomic numbers and mass number of a nucleus when it emits an α-particle?
15. What is the change in atomic number and mass number of a nucleus during negative β-decay?
16. What is the change in atomic number and mass number of a nucleus during positive β-decay?
17. What happens to the atomic number and mass number of the nucleus during a γ-decay?
238
18. 92U emits an α-particle and two β-particles. Write the atomic number and mass number of the daughter
nucleus.
19. Give examples for controlled and uncontrolled nuclear fission reactions.
20. What happens to the future of the sun when the hydrogen burning stops?
21. Define the terms (i) mass defect and (ii) binding energy of a nucleus.
Three mark questions
1. Name the three isotopes of hydrogen and write their masses.
2. Explain how neutrons were discovered.
3. Mention any three characteristics of a nucleus.
4. How the size of the nucleus is experimentally determined? Explain.
5. Show that the density of the nucleus is independent of its mass number.
6. Write any three characteristics or nuclear forces.
7. Show graphically the variation of potential energy of a pair of nucleons as a function of their
separation and explain.
8. What is a binding energy curve? Explain the main features of it.
9. What is radioactive decay? How many types of decay are there in nature? Which are they? (K)
10. What is nuclear fission? Explain with example. (U)
11. What is nuclear fusion? Explain with example. (U)
12. Arrive at the relation between activity and decay constant of a radioactive sample. (U)
13. Derive the expression for the half-life of a radioactive nuclide. (U)
14. Explain alpha decay by giving an example and when is it possible? (U)
15. Write three characteristics of neutrinos. (K)
16. What is negative β-decay? Explain with example. (U)
17. What is positive β-decay? Explain with example. (U)
18. What is γ-decay? Explain with example. (U)
19. Estimate the energy released during the fission of uranium. (A)
20. Explain how controlled chain reaction is sustained in the nuclear reactors. (U)
21. Draw a schematic labeled diagram of a nuclear reactor based on the thermal neutron fission. (S)
22. Explain why very high temperature is essential for fusion reaction. (U)
Five mark questions
1. Explain the characteristics of nucleus. (K)
2. What are the conclusions drawn by observing the binding energy curve? (U)
3. State radioactive decay law and arrive at 𝑁 = 𝑁0𝑒− 𝑡 where the symbols have their usual
meaning. (U)
4. Show graphically, the variation of binding energy per nucleon with the mass number and also explain
how energy is released in the process of nuclear fission and nuclear fusion. (S) (U)
5. Distinguish between nuclear fission and nuclear fusion. (U)
6. Obtain the expression for the number of atoms present in a radioactive sample in a given instant
of time.(U)
7. Define half-life of a radioactive element. Derive the expression for half of a radioactive
element in terms of decay constant. (U)
8. Deduce the relation between half-life and mean life of a radioactive substance. (U)
9. Explain how electricity is generated in a nuclear reactor. (U)
Numerical Problems
1. One gram of a radioactive substance disintegrates at the rate of 3.7X1010 disintegrations per
second. The atomic mass of the substance is 226. Calculate its mean life. [2282 years]
2. Find the binding energy of an α-particle from the following data.
Mass of the helium nucleus=4.001265 a.m.u
Mass of the proton = 1.007277 a.m.u
Mass of the neutron = 1.00866 a.m.u (A) [7.10525 MeV]
14.
3. Calculate the mass defect and specific binding energy of 7N Given: The rest mass of nitrogen
nucleus is 14.00307 amu. Mp = 1.00783amu, Mn = 1.00867amu (A)
[Ans: Δm = 0.11243 amu, S.BE = 7.48 MeV]
4. Calculate the energy of released in the following fusion reaction of 1Kg of 1H2.
2 2 3 1
1H 1 H He 0 n Q
2
Given: Mass of 2He3 = 3.0161amu, mass of 1H2 = 2.0141amu and mass of neutron
1
0n = 1.0087amu. (A) [Ans: Q=4.769 X 1026MeV]
5. The half-life of a radioactive substance is 30s calculate i) the decay constant and ii) time taken
to the sample to decay by 3/4th of the initial value? (A)
[Ans: λ=0.0231 per sec, t=60 sec]
6. Calculate the half- Given mass of
23
Radium -226 gram and 226 gram of radium consists of 6.023 × 10 atoms. (A)
[Ans: T = 5 X 1010 Sec, τ = 7.2 X 1010 Sec]
7. The half-life of a radioactive element is 4 × 108 years.Calculate its decay constant and mean
life. (A) [Ans: λ = 1.733 X 10-9 Per Year, τ = 5.772 X 108 Years]
8. Find the activity in curie of 1g of radon: 222, whose half-life is 3.825 days.
Avogadro number = 6.023 × 1023, given; 1 curie = 3.7 × 1010 disintegrations per second. (A)
[Ans: R = 1.5375 X 105 Ci]
9. Determine the mass of Na22 which has an activity of 5mci. Half-life of Na22 is 2.6 years.
Avogadro number = 6.023 × 1023 atoms. (A) [Ans: m = 7.996 X 10-10 Kg]
10. Calculate the mass in gram of radium 226. Whose activity is 1 curie and half-life is 1620 years.
(Avogadro’s number = 6.023 × 1023) (A) [Ans: m = 1.024 g]
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CHAPTER-14
SEMICONDUCTOR ELECTRONICS
One mark questions
1. Which devices were used instead of transistors before its invention? (K)
2. On what principle cathode ray tube (CRT) works? (K)
3. What is a semi-conductor? (K)
4. Give an example of elemental semi-conductor. (U)
5. Give an example of organic semi-conductor. (U)
6. How ‘energy bands’ are formed in a solid? (U)
7. What is a ‘valence band’ in solids? (U)
8. Where do the ‘conduction band’ is situated in solids? (K)
9. Do the ‘conduction band’ is filled with electrons or empty in solids normally? (K)
10. What is the value of energy gap in conductors? (K)
11. What is the value of energy gap in semiconductors? (K)
12. What is the value of energy gap in insulators? (K)
13. What is forbidden energy gap? (K)
14. What is fermi energy? (K)
15. For which type of material conduction band overlaps with valence band? (K)
16. How does conductivity of semiconductor change with temperature? (U)
17. What is the unique property of the semiconductor which is used is electronics? (U)
18. What is a ‘hole’ in semi-conductor? (U)
19. What are intrinsic semi-conductors? (K)
20. What are extrinsic semi-conductors? (K)
21. With the help of a diagram show that an intrinsic semi-conductor behaves as insulator at 0K (S)
22. What is meant by ‘doping’ a semi-conductor? (K)
23. What is the advantage of doping a semiconductor? / OR (U)
24. What is the necessity of doping of a semi-conductor? (U)
25. Which type of extrinsic semi-conductor is obtained by doping with pentavalent impurity? (K)
26. Mention the name of the extrinsic semi-conductor which is doped with trivalent dopant. (K)
27. Doping silicon with indium (boron/aluminum) leads to which type of semiconductor? (K)
28. Doping in silicon with phosphorous (arsenic, antimony) leads to which type of semiconductor? (K)
29. What is diffusion current in a p-n junction diode? (U)
30. What is ‘drift current’ in a p-n junction diode? (U)
31. What is barrier potential in a semiconductor diode? (U)
32. What is depletion region in a semiconductor diode? (U)
33. Write the circuit symbol of p-n junction diode. (S)
34. When the diode is said to be forward biased? (K)
35. When the diode is said to be reverse biased? (K)
36. What happens to the width of the depletion region when the diode is forward biased? (K)
37. What happens to width of the depletion region when the diode is reverse biased? (K)
38. What is breakdown voltage of a semiconductor diode? (U)
39. What is cut-in voltage of a semiconductor diode? (U)
40. What is reverse saturation current? (U)
41. What is dynamic resistance in a semiconductor diode? (U)
42. What is a rectifier? (K)
43. What is a half-wave rectifier? (K)
44. What is a full-wave rectifier? (K)
45. How to get a steady d.c output from the pulsating d.c output of a full wave rectifier? (U)
46. What are filter circuits in rectifiers? (K)
47. What is internal field emission or field ionization in a Zener diode? (U)
48. Symbolically represent a Zener diode. (S)
49. In which region Zener diode is operated in voltage regulator? (K)
Two mark questions
1. Write two advantages of semi-conductor devices over vacuum tubes. (K)
2. Distinguish between intrinsic and extrinsic semiconductors. (U)
3. Distinguish between p-type and n-type semiconductors. (U)
4. How hole current is developed in intrinsic semi-conductors? Explain. (U)
5. What are extrinsic semiconductors? Mention the types of extrinsic semiconductor. (K)
6. Why majority charge carriers increase on doping a pure semiconductor? (U)
7. Draw the graphs showing the V-I characteristics of a p-n junction diode a) in forward bias b) in
reverse bias. (S)
8. Distinguish between conductors, semi-conductors and insulators on the basis of property of
conductivity.(U)
9. Classify on the basis of electrical resistivity metals, semi-conductors and insulators. (U)
10. Which are the three different types of compound semi-conductors, give an example for each. (K)
11. Distinguish between conductor, semiconductor and insulator based on band theory of solids. (K)
12. What is an intrinsic semiconductor? Explain the variation of conductivity with temperature in it. (U)
13. Explain how a p-n junction is formed in a semiconductor. (U)
14. With suitable circuit diagram, explain the V-I characteristics of a semiconductor diode under
forward bias. (U) (S)
15. Explain the V-I characteristics of a semiconductor diode under reverse bias by drawing a suitable graph.
(U) (S)
16. Explain why reverse current suddenly increases at the breakdown region in a Zener diode? (U)
17. With the help of a circuit explain how a capacitor filters ripples of pulsating d.c. in rectifier. (U)(S)
18. What is a Zener diode? How it is fabricated? (U)
Five mark questions
1. Describe the action of a semiconductor diode under forward and reverse bias with I-V diagrams.
2. What is a rectifier? Explain with necessary circuit diagram, the construction and working of a half wave
rectifier. (U) (S)
3. What is a rectifier? Describe the construction and working of a full wave rectifier by drawing input and
output waveforms. (U) (S)
4. Explain with necessary diagram how a Zener diode acts as a voltage regulator. (U) (S)
5. Draw circuit arrangement for studying input and output characteristics of n-p-n transistor in CE configuration
and explain its action with the help of graphs. (U) (S)
6. Explain with necessary circuit diagram the working of n-p-n-transistor as an amplifier in CE mode. (U) (S)
7. Explain with necessary circuit diagram the working of n-p-n-transistor as a switch. (U) (S)
8. With a necessary circuit describe the working of a tuned collector oscillator. (U) (S)
Numerical problems
1. The input frequency of a rectifier is 100 Hz. Calculate the output frequency if the rectifier is (a) half wave
rectifier (b) full wave rectifier. (A) [50HZ, 100Hz]
2. An amplifier of voltage gain 12 is connected in series with another amplifier of voltage gain 20. If the input
signal is 20 mV, calculate the output voltage of ac signal. (A) [4.8 V]
3. An LED is constructed from a p-n junction, based on a certain Ga-As-P semi-conducting material whose
energy gap is 1.9 eV. Calculate the wavelength of the light emitted by this LED, also identify the colour of the
emitted light. [650 nm, Red in colour]
4. A silicon transistor is connected in CE mode to use it as a switch, in which base voltage is varied from 0-6.0 V.
the transistors dc current gain is 300, base resistance 150 KΩ, collector resistance 1.5 KΩ & collector voltage 6
V. Assume that the transistor is saturated and if VCE =0V, VBE=1V, calculate the minimum base current for
which the transistor will reach saturation and hence determine input voltage when the transistor is switched
on. (A)
[13.3 µA, 1.995 V]
5. The current amplification factor of CE transistor amplifier is 110. An audio signal voltage across 2.5 KΩ
collector resistor is 2.5V, calculate base current. (A) [9µA]
16 14
6. One cubic meter of silicon is simultaneously doped with 3.05X10 atoms of arsenic and 5X10 atoms of
indium. If intrinsic carrier concentration ni =4X1016, calculate the number of electrons and holes. (A)
7. A p-n junction diode is connected in series with 5kΩ across a battery of emf 5.7V and negligible internal
resistance in such a way that the diode is forward biased. If the barrier potential in diode is 0.7V, calculate the
current through the diode. What is the resistance that should be combined with 5kΩ so that the current
through the diode becomes 3mA? (A)
8. The electrical conductivity of a semiconductor increases when an electromagnetic radiation of
wavelength shorter than 2480nm is incident on it. Calculate the energy band gap in eV for the
semiconductor. (A).
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