9
Explain with the help of a labelled circuit diagram, how you will find the
resistance of a combination of three resistors, of resistance R,, R, and R,
joined in parallel. Also mention how you will connect the ammeter and
voltmeter in the circuit when measuring the current in the circuit and the
potential difference across one of the three resistors of the combination.
Answers
Answer:
Explanation:
SOLUTION
The given figure shows a circuit consisting of three resistors R1, R2 and R3 connected in parallel. The total current in the circuit (I) gets divided among the three resistors as I1, I2 and I3.
Thus,
I = I1 + I2 + I3
Applying Ohm’s law to each resistor,
I
1
=
V
R
1
I1=VR1
I
2
=
V
R
2
I2=VR2
I
3
=
V
R
3
I3=VR3
Let the equivalent resistance of the circuit be Req.
Applying Ohm’s law to the equivalent circuit,
I
=
V
R
e
q
I=VReq
Using these,
V
R
e
q
=
V
R
1
+
V
R
2
+
V
R
3
VReq=VR1+VR2+VR3
1
R
e
q
=
1
R
1
+
1
R
2
+
1
R
3
1Req=1R1+1R2+1R3
An ammeter has to be connected in series with the combination of all three resistors so that the current passes through the ammeter becomes equal to the total current through the circuit.
The voltmeter has to be connected in parallel to that resistor across which the potential difference has to be measured.