First slide

Sources of emf and Kirchhoff's laws

Question

In the circuit shown:

Moderate

A

the potential at P is - 7.5 V
B

the potential at Q is -1 V
C

the potential at R is zero
D

the potential at S is zero

Solution

The current in the circuit I $= \frac{(20 - 10)}{(7.5 + 0.5 + 1 + 1)}$
$= \frac{10}{10} = 1 amp$
The potential difference across $PS, V_{PS} = 7 .5 \times 1$
$= 7.5 V$
The potential difference across $Q, R, V_{QR} = 1 \times 1$
$= 1 V$
As point G is connected to earth, hence potentials of R and S are zero.
The direction of the current in the circuit is from P to S, hence point P is at higher potential.
$∴ V_{p} = 7 .5 V$
$Similarly, V_{Q} = - 1 V$
$∴$ Hence (b), (c) and (d) are correct.

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