question_answer

A. sheet of aluminium foil of negligible thickness is introduced between the plates of a capacitor. The capacitance of the capacitor

A)  decreases                         

B)  remains unchanged

C)  becomes infinite

D)  increases

Correct Answer: B

Solution :

Aluminium is a metal, so when we insert an aluminium foil, equal and opposite charges appear on its two surfaces. Since, it is of negligible thickness, it will not effect the capacitance. Alternative: From the formula, \[C=\frac{{{\varepsilon }_{0}}A}{d-t+\frac{t}{K}}\] \[\Rightarrow \]               Here,\[K=\infty \]and\[t\to 0\] So,          \[C=\frac{{{\varepsilon }_{0}}A}{d+0}=\frac{{{\varepsilon }_{0}}A}{d}={{C}_{0}}\]