Question

Two point charges of 20uC and 80uC are placed 18cm apart. Find the position where electric field is zero.

Answer 1

Answer:

at 6 cm from 20μc charge and in between 20μc charge and 80μc charge

Explanation:

• formula for electric field is kQ/R^2
• we have to consider a point (p) between 20μc to 80μc
• point p is (x) distance away from 20μc so point p is (18 - x) distance away form 80 μc
• now on point p there are 2 vectors and both are in opposite direction to each other.
• one vector on point p ( electric field on p due to 20 μc ) = k 20/x^2
• another vector on point p ( electric field due to 80 μc ) = k80/(18-x)^2

• so E net on point p = k20/x^2 - k80/(18-x)^2

                                         = k20(1/x^2 - 4/(18-x))

                                         = k 20 ( 1/x - 2/(18-x))

• now we have to find a point where Enet = 0
• let that point be p

• so 0 = k 20 (1/x - 2(18-x)

             0 = 1/x - 2/ (18-x)

             1/x = 2/ (18-x)

             18 - x =  2x

            18 = 3x

            x = 6 cm

• electric field is zero at 6 cm from 20μc charge and between 20μc charge and 80 μc charge......

hope it's useful................