Question

Take the potential of the point B in figure to be zero. (a) Find the potentials at the points C and D. (b) If a capacitor is connected between C and D, what charge will appear on this capacitor?

Answer 1

(a) The capacitance of the two rows connected in parallel is given by

`C_1 = (4 xx 8)/(4+8) = 8/3  "uF" and C_2 = (3 xx 6)/(3+6) = 18/9 "uF" = 2  "uF"`

As the two rows are in parallel, the potential difference across each row is the same and is equal to 50 V.

The charge on the branch ACB with capacitance `8/3 "uF"` is given by

`Q = (8/3  "uF") xx (50 V) = 400/3 "uC"`

The charge on the branch ADB with capacitance `2  "uF"` is given by

`Q = C xx V`

`Q = 2  "uF" xx 50 = 100  "uC"`

The potential at point D is given by

`V_D = q/C_1 = (100  "uC")/(6  "uF")`

`V_D = 50/3 V`

Similarly, the potential at point C is given by

`V_c = 50/3 V`

(b) As the potential difference between points C and D is zero, the bridge remains balanced and no charge flows from C to D. If a capacitor is connected between points C and D, then the change on the capacitor will be zero.