Activity 1

Objective:

To measure resistance, voltage (AC/DC), current (AC) and check the continuity of a
given circuit using multi-meter.

Apparatus required:

Multi-meter, carbon resistance of different values, cell and any circuit.

Theory:

Carbon resistance are made from mixture of conductor and non-conductor moulded
into tools by heating. The resistance depends upon the percentage of carbon added.

A carbon resistance consists of four colours. First two colours give the significant figure
and the third colour gives the multiplier. The fourth colour represents tolerance or
accuracy.

Colour Figure Multiplier

Black 0 100 Tolerance of fourth
Brown 1 101 colour is
Red 2 102 Gold: 5%
Orange 3 103 Silver:10%
Yellow 4 104 No colour: 20%
Green 5 105
Blue 6 106
Violet 7 107
Grey 8 108
White 9 109

Procedure:

To measure resistance:

1. Note the colour marked on the carbon resistor and calculate the value as
Eg. Red Brown Green Glod
2 1 x 10 5
±5%
Ans. 21 x 105 ±5% or 2100 KΩ ±5%
2. Touch the two leads of multi-meter to the leads of the resistor and note the
deflection. This will give the value of the resistance.
3. Observation:

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 Resistance Colour of the rings Resistance Multi-
used I II III IV using meter
colour Reading
code R’Ω
RΩ
R1
R2

Difference = R – R’
R1 = _____Ω
R2 = _____Ω

To measure DC voltage:

1. Select DC voltage by turning the selector switch to suitable range

2. Touch the black lead of multi-meter to -ve terminal of battery and red lead to +ve
terminal of the battery and note down the multi-meter reading which gives the
DC voltage of the battery.

To measure the AC voltage:

1. Select AC voltage by turning the selector switch to suitable range say 600 V.
2. Insert the ends of multi-meter to the AC switch and note down the reading of
multi-meter. This gives the AC voltage.

Continuity of the given circuit:

1. Select the selector switch to ohm range. MΩ

2. Touch the ends of A and B. Full scale deflection indicates continuity.

Result:

The resistance measured by muti-meter have a very close agreement with colour code
within the limit of tolerance.

AC and DC voltages marked on voltage sources match with voltage measured by multi-
meter.

Multi-meter shows full deflection indicating the continuity of the given circuit.

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 Activity 2

AIM:

To assemble the components of a given electrical circuit.

Apparatus and Material required:

Resistor, ammeter, (0-1.5A) voltmeter (0-5V ), battery, one way key, rheostat, sand
paper, connecting wires.

Procedure:

1. Connect the components as shown in Figure.

2. After closing the key K, check that the voltmeter and ammeter show deflections
on the right-hand side.
3. Check the continuity of the assembled circuit using a multi-meter.

Result:

The components of the electrical circuit were assembled.

Precautions:

1. The positive terminal of the battery should be connected to the positive terminal
of ammeter and positive terminal of the voltmeter.
2. The ammeter should be connected in series with the resistor and the voltmeter
should be connected in parallel with the resistor.
3. Sand paper should be used to clean the ends of connecting wires and leads of
the component terminals.

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 Activity 3

Aim:

To study the variation in potential drop with length of a wire for a steady current.

Apparatus and Material required:

Potentiometer, battery eliminator of constant voltage, dc power supply or lead

accumulator, voltmeter and ammeter of suitable range, plug key, jockey, rheostat,
connecting wires, etc.

Principle:

Potentiometer, battery eliminator of constant voltage, dc power supply or lead

accumulator, voltmeter and ammeter of suitable range, plug key, jockey, rheostat,
connecting wires, etc.

Mathematically V∝ I

Procedure:

1. Set up the electrical circuit as shown in Figure.

2. Record the zero error if voltmeter pointer shows anomalous deflection. Keep the
jockey ‘J’ with its indicator facing the 10 cm mark on the meterscale fixed along
the wire AB.
3. Plug in the key ‘k’ , pass the jockey at this point on the wire and note the
voltmeter reading.
4. Now slide the jockey ‘J’ along the wire away from its ends A and go on nothing the
voltmeter reading by pressing the jockey at 20, 40, 60 and 80 cm length on wire.
5. Record the observations.

Observations:

Range of the voltmeter = ... V

Least count of the voltmeter = ...V

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 S.no. Length of wire for PD (l in cm) Voltmeter reading (V) Potential drop with
length (V/l)
1 20 cm
2 40 cm
3 60 cm
4 80 cm
5 100 cm

Calculations:
𝑉
The ratio φ = is calculated. It is the potential gradient of the wire. Its value is almost
𝑙
constant.

Result:

The potential drop with length is ______ V/cm

Precautions:

1. Do not press the wire too hard with the jockey while noting down the
observations or else there is a possibility that the wire will become non-uniform
(diameter will change) at these points during the course of time.
2. The current in the wire should remain constant throughout the experiment. To
ensure this, current should be drawn intermittently for short duration of time. It
should be monitored by an ammeter and readjusted whenever necessary, with
the help of a rheostat.

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 Activity 4

Aim

To identify a diode, a LED, a transistor, an IC, a resistor and a capacitor from a mixed
collection of such items.

Apparatus and material required:

Multi-meter, a collection of diode, LED, transistor, IC, resistor and capacitor.

Principle:

• A diode is a two-terminal device. It conducts when forward biased and does not
conduct when reverse biased. It does not emit light while conducting.
• A LED (light emitting diode) is also a two-terminal device. It conducts when
forward biased and does not conduct when reverse biased. It emits light while
conducting.
• A transistor is a three-terminal device. The terminals represent emitter (E), base
(B) and collector (C).
• An IC (integrated circuit) is a multi-terminal device in the form of a chip. But
some may have only three terminals, e.g. 7805, 7806, 7809, 7912.
• A resistor is a two-terminal device. It conducts equally in both directions.
• A capacitor is a two-terminal device. It does not conduct but stores some charge
when dc voltage is applied.

Procedure:

1. Check the physical appearance of the component.

(a) If it has four or more terminals and has the appearance of a chip (black
rectangular block), then it is an IC.
(b) If it has three terminals, the component may be a transistor.
(c) If the component has two terminals, it could be a resistor, a capacitor, a
diode or a LED.
(d) Look for colour bands, if it has a typical set of three colour bands followed by
a silver or gold band, the component is a resistor.

Observations:

S.no. No. of legs Name of device

1 Multi leg IC
2 Three Transistor
3 Two Capacitor, diode, LED or resistor

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 S. no. Current flow Name of device
1 Unidirectional and emits no light Diode
2 Unidirectional and emits light LED
3 Both directions (steady current) Resistor
4 Initially high but decays too Capacitor

Result:

A diode, a LED, a transistor, an IC, a resistor and a capacitor are identified respectively
from a mixed collection.

Precautions:

While obtaining resistance of any component, clean its leads properly.

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 Activity 5

Aim:

To study the effect of intensity of light (by varying distance of the source) on a LDR (Light
Dependent Resistor).

Apparatus and material required:

LDR, two power supplies (12 V each), key, milliammeter (0-500mA), voltmeter (0-10V), a
resistance of 47 Ω, a 12 V lamp, connecting wires.

Principle:

Light dependent resistor or a photoresistor is a device that is sensitive to light. Its

resistance varies according to the intensity of light incident on it. It is made from a
semiconductor material with light resistors to have light sensitive properties, one such
materials is, cadmium sulphide. Snake–like tracks are made of cadmium sulphide on
thin metal films.

LDR has a high resistance due to the fact that majority of electrons are locked into the
crystal lattice and not free to move. As light falls on the lattice, some of the electrons
get sufficient energy to break free the crystal lattice to conduct electricity.

A typical LDR has a resistance of 1 MΩ in total darkness and a few hundred-ohm

resistance in bright light.

Procedure:

1. Set the multi-meter for measurement of resistance and adjust the multi-meter
two adjustments to have the maximum deflection.
2. Cover the LDR so that no extra light falls on it.
3. Touch the metallic probes to the metal rods LDR and read the value of resistance
when the source is kept at a distance of 2 cm, about the LDR.
4. Move the source to 5 cm distance from LDR and note the reading of the multi-
meter.
5. Thus take 3 to 4 observations by moving the source to different points.

Observations:

S.no. Distance of source from LDR (cm) Resistance of LDR (KΩ)

1 5 cm
2 10 cm
3 15 cm
4 20 cm
5 25 cm

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Result:

As distance increases, intensity of incident light decreases and resistance of LDR

increases.

Precautions:

1. LDR is placed normally to the light source so that angle of incidence of light rays
remain constant and normal throughout the experiment.
2. All the connections should be made tight.

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 Activity 6

Aim:

To observe refraction and lateral deviation of a beam of light incident obliquely on a

glass slab.

Apparatus and material required:

Drawing board, rectangular glass slab, white sheet of paper, drawing pins, a metre
scale, al pins, protractor, sharp pencil and eraser.

Principle:

When a ray of light is incident on a rectangular glass slab, it is refracted through it. It
emerges out of the slab parallel to the direction of the incident ray. The emergent ray
suffers only a lateral displacement. For a given angle of incidence and a pair of media,
the lateral deviation is proportional to the thickness of the glass slab.

Procedure:

1. Fix a white sheet of paper on the drawing board with the help of drawing pins.
2. Place the glass slab lengthwise symmetrically at the centre of the paper sheet
and mark its boundary ABCD (refer figure) on the paper sheet with a sharp
pencil.
3. Draw a normal at a point F on the face AB. Draw a line EF, representing the
incident ray, making an angle i the angle of incidence with the normal.
4. Fix two al pins P and Q with sharp tips, about 8 to 10 cm apart, vertically on the
line EF
5. Observe the images of the two pins through the face opposite of the glass slab.
Fix two more al pins R and S about 8 to 10 cm apart, vertically on the white paper
sheet carefully with their tips in line with the tips of the images of P and Q. Take
care that the tips of all the al pins appear to be on a straight line.
6. Remove the glass slab and mark the pin prick positions of the al pins on the
white paper sheet with a pencil. Draw a straight-line GH, representing the
emergent ray, passing through the points marked R and S, meeting the face CD at
G.
7. Draw the line FG to represent the refracted ray. Draw a normal at the point G on
the face CD; making an angle of emergence e with the normal. Measure the
angle of incidence i and angle of emergence e with a protractor. Write the values
of these angles on the white paper sheet.
8. Extrapolate EF forward to meet the face CD of the glass slab at O. Draw the
perpendicular OL to the line GH.

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 9. Check if the emergent ray GH is parallel to the incident ray EF along the original
direction. It is laterally deviated by a perpendicular distance OL. Measure the
lateral deviation OL = d and also the thickness of the glass slab.

Observations:

s.no. Thickness Angle of incidence Angle of emergence Lateral

of the Degree Radians Degree Radians displacement
glass slab (d) 10-2 m
(t )10-2 m
1 30°
2 45°

Result:

1. The ray of light emerging from a glass slab is parallel to the incident ray direction,
but is laterally deviated.
2. The lateral deviation of the emergent ray with respect to the incident ray is
directly proportional to the thickness of the glass slab.

Precautions:

1. Rectangular slab should be perfectly smooth

2. The angle of incidence should be between 30° and 60°
3. All pins should be in a straight line

Source of error:

1. There shouldn’t be any air bubbles in glass slab

2. The measurement done by the protractor should be accurate.

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