Question

The maximum electric field that a dielectric medium of a capacitor can withstand without break down (of its insulating property) is called its

• A. polarisation
• B. capacitance
• C. dielectric strength
• D. None of these

Answer 1

Answer: (C)

The maximum electric field that a dielectric medium can withstand without break down (of its insulating property) is called its dielectric strength; for air it is about $3\times 10^{6}V{m}^{-1}$. For a separation between conductors of the order of $1cm$ or so, this field corresponds to a potential difference of $3\times 10^{4}V$ between the conductors. Thus, for a capacitor to store a large amount of charge without leaking, its capacitance should be high enough so that the potential difference and hence the electric field do not exceed the break down limits. Put differently, there is a limit to the amount of charge can be stored on a given capacitor without significant leaking.