Question

Two charges 5 uC and 20 uC are placed on two
concentric circles of radius 10 cm and 20 cm
respectively lying in x-y plane. The potential at
centre is
(1) 1.35 x 10^4 V
(2) 13.5 x 10^4 V
(3) 135 x 10^4 v
(4) Zero​

Answer 1

Answer: (3) 135 x 10^4 V

Explanation:

1) We know,

Potential due to any charged particle 'q' at a distance 'r' is given by

$V=\frac{kq}{r}$

where

k = Coulombs Constant

$k=9 *10^9 \:units$

2)Then ,

At the centre potential will be due to charges q-1= 5uC and q-2=20uC .

r-1=10cm ,r-2 = 20cm

Thus,

$V_{centre}= \frac{kq_1}{r_1}+\frac{kq_2}{r_2}\\ \\=\frac{k*5\mu C}{10cm}+\frac{k*20\mu C}{20 cm} \\ \\=\frac{k *5 *10^{-6}}{10 x10^{-2}}+\frac{k * 20*10^{-6}}{20 *10^{-2}} \\ \\=\frac{k*10^{-4}}{2}+\frac{k*10^{-4}}{1}\\ \\=\frac{9*10</p><p>^9*10^{-4}}{2}+\frac{9 * 10^9 *10^{-4}</p><p>}{1}\\ \\=\frac{9 *10^{5}*3}{2}\\ \\= 135 *10^4V$

Hence, Potential at the centre due to given two charges is 135 x 10^4 V.