Question

Two point charges +10nC and +30nC are 1m apart. Find the electric potential at a point between them which is at a distance of 0.8m from the stronger charge. Find the point between the charges where the potential due to them are equal.

Answer 1

Given :

Charges = +10 nC and +30 nC

Distance between the charges = 1 m

To find :

Potential at point 0.8m away from stronger charge and the point where the potential due to charges are equal .

Solution :

Electric potential = k * Q / r

where , Q is charge ,

r is distance ,

and , k is contant = 9.0 * 10^9 N * m^2 / C^2

Now,

Electric potential = ( 9.0 * 10^9 * 10 ^ (-9) / 0.2 ) + ( 9.0 * 10^9 * 30 ^ (-9) / 0.8 )

=> electric potential = 450 + 337.5 = 787.5 V

when potential due to charges are equal ,

k * 10 ^ (-9) / r = k * 30 ^ (-9) / (1 - r)

=> 10 / r = 30 / (1 - r)

=> 10 - 10r = 30r

=> 40 r = 10

r = 0.25

The potential at point 0.8m away from stronger charge is 787.5 V and the point where the potential due to charges are equal is 0.25 m away from 10 nC charge .