Question

The electric field of two long coaxial cylinders is represented by lines of force as shown above. The charge on the inner cylinder is +Q. The charge on the outer cylinder is

(A) +3Q 

(B) +Q 

(C) 0 

(D) – Q 

(E) –3 Q

Answer 1

The correct option is: (E) –3 Q

Explanation:

Compared to the +Q charge at the center, the charge on the outer surface of the outer cylinder has twice the magnitude and is of opposite sign (so it is –2Q). There is also an equal and opposite charge induced on the inner surface of the outer cylinder making the total charge on the outer cylinder –2Q + –Q.