Question

Q.1. In Fig, the potential difference between points A
and B is 240V. If the mid-point M of AB is earthed, A
what are the potentials of A and B?
​

Answer 1

The two 3μF capacitors in parallel can be combined into a single capacitor (C) with an equivalent capacitance of C=3+3=6μF

Now, the remaining two 3μF capacitors are in series with C. This can be also combined in a single capacitor of capacitance C

′

.

C

′

1

=

3

1

+

3

1

+

6

1

C

′

=

5

6

μF

Now, in series charge across all the capacitors is same and voltage add up to give the equivalent voltage.

Let required voltage across the 6μF capacitor be V and the voltage across C

′

be V

′

Let charge across each of the two capacitors be Q

Using definition of capacitance and same charge,

Q=Q

6V=

5

6

V

′

Given V+V

′

=60

Solving above two equations, V=10 V