Page 53 - Physics - XII

step down upto 6 V by using step-down transformer and the multimeter is connected to the two ends of the
secondary coil of step-down transformer. By adjusting the rheostat, the multimeter reading for A.C. voltage
drop across the resistor is noted.

P S

X Z

A.C. mains Multimeter set in A.C.
RB voltage measuring mode
Y

Step down K
transformer
Fig. 2.5: Use of multimeter as an A.C. voltmeter

To Check the Conti nuity of an Electrical Component

To check the continuity of any electrical component, resistance of the component is measured. A very low
resistance (≤ 0.1 Ω) between the two ends of a component indicates that the component under test has a

short circuit. If the component under test shows infi nite resistance, it indicates the discontinuity.

Procedure
Measurement using Analog Multimeter

Measurement of Resistance

1. Set the multimeter in resistance measuring mode. Connect the red and black probes to the multimeter.
The end of test leads should not have any insulating layer on them.
2. Touch free end of both the leads and adjust the zero adjustment knob till the multimeter reads zero ohm
on resistance scale.

3. Separate the two metallic ends of the test probes (leads) and connect the resistance box with the
multimeter.
4. Now, insert a known resistance R in the circuit by taking out a resistance key from the resistance box
and note the multimeter reading R indicating the value of resistance of the resistor used in the circuit.
M
Repeat this step four more times by taking out diff erent resistors.
5. Carefully observe the reading in the non-linear scale, noting that its zero lies at the extreme right of the

scale. Use the multiplication factor appropriately to the range selected.
e.g. 4 divisions of defl ection in R × 100 scale means resistance measured is 4 × 100 Ω = 400 Ω.

Measurement of D.C. Voltage

6. Take a source of D.C. like a battery.
7. Set the multimeter pointer to D.C. voltage range.
8. Set the test probes in the multimeter socket with polarity. It is a convention to use red lead as positive
and black lead as negative.

9. Connect the free end of black lead with negative terminal of the battery and that of red lead to the
positive terminal of the battery.
51