Ncert Exercises & Solutions

Refer to the arrangement of charges in the figure and a Gaussian surface of radius R with Q at the centre. Then:

a.	total flux through the surface of the sphere is $\frac{- Q}{ε_{0}}$ .
b.	field on the surface of the sphere is $\frac{- Q}{4 π ε_{0} R^{2}}$ .
c.	flux through the surface of the sphere due to 5Q is zero.
d.	field on the surface of the sphere due to -2Q is the same everywhere.

Choose the correct statement(s):
1. a and d
2. a and c
3. b and d
4. c and d

(2) Hint: Use Gauss' Law.

Step 1: Find the net flux passing through the surface.

Gauss' law states that the total electric flux of an enclosed surface is given by

\frac{q}{ε_{0}}

where q is the charge enclosed by the surface. Thus, from the figure,

Total charge inside the surface is = Q - 2Q = -Q

∴

Total flux through the surface of the sphere

= \frac{- Q}{ε_{0}}

Step 2: Find the flux due to the 5Q charge.

Now, considering charge 5Q. Charge 5Q lies outside the surface, thus it makes no contribution to electric flux through the given surface.