Question

Fig. (a) shows an imaginary cube of edge $L/2$. A uniformly charged rod of length L moves towards left at a small but constant speed $\upsilon$. At $t=0$, the left end just touches the centre of the face of the cube opposite it. Which of the graphs shown in Fig. (b) represents the flux of the electric field through the cube as the rod goes through it?

• A. a
• B. b
• C. c
• D. d

Answer 1

The correct option is D d

When the rod will start going in, the flux due to the electric field will increase through the cube. It will reach its maximum with $L/2$ length is inside. It will remain at the maximum point until the rest $L/2$ passes through it. Then again the flux will starts decreasing until the whole rod comes out.

So, the graph $D$ is the correct answer.