Question

The following operation can be performed on a capacitor:
X connect the capacitor to a battery of emf E.
Y disconnect the battery.
Z reconnect the battery with the polarity reversed.
W insert a dielectric slab in the capacitor.

• A. In XYZ (perform X, then Y, then Z) the stored electric energy remains unchanged and no thermal energy is developed
• B. The charge appearing on the capacitor is greater after the action XWY than after the action XYW.
• C. The electric energy stored in the capacitor is greater after the action WXY than after the action XYW.
• D. The electric field in the capacitor after the action XW is the same as that after WX.

Answer 1

Answer: (B), (C), (D)

The correct options are
B The charge appearing on the capacitor is greater after the action XWY than after the action XYW.
C The electric energy stored in the capacitor is greater after the action WXY than after the action XYW.
D The electric field in the capacitor after the action XW is the same as that after WX.

For option (B) solution : In XWY, charge on capacitor plate =KCE

In XYW, charge on capacitor plate = CE

For option (C) solution : In WXY, U = $\frac{1}{2}KC{E}^2$

In XYW, U = $\frac{C{E}^2}{2K}$

For option (D) solution : 2 both cases, electric field = $\frac{E}{d}$ .