Activity :2
Object-To measure resistance, voltage (a.c./d.c.), current
a.c./d.c.)and check continuity ofagiven circuit using a mmultimeter.
Apparatus required-Multimeter d.c. circuit and a.c.
,
circuit.
Method--() With the d.c. source:
(1) First complete the electric circuit shown in Fig. 46 for
which a battery is joined between the terminals X and Y to form
a d.c. circuit.
(2) Now to measure the dc. voltage applied between the
terminals C and D, the knob of multimeter is adjusted in the d.e.
voltage range 0-15 V(1f the e.m.f. of the battery used is 12 V). Then
the end of black lead connected to the negative end of multimeter
is joined at the end D of the rheostat, while the end of red lead
connected to the positive end multimeter is joined to the end C of
the rheostat. Note the readings of multimeter by varying the sliding
terminal D ofthe rheostat. This measures the d.c. voltage between
the terminals C and D
12 V BATTERY
RHEOSTAT Rh
-
D R.B
E100
B
Fig. 46.
(3) Now to measure current in the dc. circuit, the knob of
multimeter is adjusted in the d.c. current range 0-100 mA The
end of black lead connected to the negative end of multimeter 1s
joined at the end B (which is connected to the negative end of
battery), while the end of red lead connected to the positive end of
multimeter is joined to the end A (which is connected to the positive
end of battery). Note the readings of multimeter by changing the
current in circuit by means of rheostat.
(4) Now to test the continuity of circuit by the multimeter, the
plug is removed from the key K and adjust the knob of multimeter
in the lowest range of resistance. Then touch the two ends of red
and black leads of the multimeter and adjust the zero adjustment
knob such that maximum deflection is obtained in the multimeter
(i.e., its pointer reaches the zero mark at the right end).
Now to test that the circuit is broken, connect the lcads of
multimeter at the ends A and B. You will find that it pointer does
not move, but remains stationary at the left end. This shows tha:
the resistance of circuit is infinite ie., the circuit is broken between
the ends A and B.
Then to test the continuity of the circuit, connect the leads of
multimeter at the ends E and F of the resistance box R, B. Now
current starts flowing in the circuit of multimeter due to which
defiection is obtained (i.e, its pointer shifts towards the nght
The reading of pointer on the scale of multimeter measures the
resistance joined in the circuit by means of the resistance box
(i)With the a.c. source
In this part ofthe experiment, the battery show in circut in Fig
46 between the teminals X and Y is replaced by the ac. soure
Then the knob of multimeter is adjusted for the measurement ofac
and the steps 2,3 and 4 described above are repeated Remember
that for the measurement of ac. voltage or curent, the ed and
black leads ofmultimeter can be connected to any termnal bocaus
there is no signiticance of polarity (+ or -) in ac
Observations-
(1) For the d.c. circuit:
Voltage range 0 15 V, Current range 0 100) mA.
Resistance range = Rx 1 2
S. No. d.c. voltage d.c. current Resistance
1 2-4 volt 90 mA Infinite between A and B
2. 3-0 volt 60 mA 100 Q between E and F
(2) For the a.c. circuit
Voltage range = 0-50 V, Current range 0-100 mA
Resistance range = R x 1 Q2
S. No. a.c. voltage a.c. current Resistance
1. 15-0 volt 70 mA Infinite between A and B
2. 25-0 volt 50 mA 100 2 between E and F
Precautions-(1) First the knob of multimeter is adjusted in
the apropriate range of voltage/current/resistance which is to be
measured and see that whether the circuit is a.c. or d.c., adjust the
knob accordingly.
(2) Each time while measuring the resistance, first the zero
adjustment is made.
(3) For the d.c. circuit, the red andblack leads respectively
from the + ve and ve marked ends of multimeter must be
-
towards the
connected such that the red lead is to the terminal
end of battery and black lead is to the terminal towards
positive
negative end of in the circuit. In the a.c. circuit, this polarity
battery
has no significance.
