Question

In case of a Van de Graaff generator, the breakdown field of air is

• A. $2 \times 10^{8} \, V\, m^{-1}$
• B. $3 \times 10^{6} \, V\, m^{-1}$
• C. $2 \times 10^{-8} \, V\, m^{-1}$
• D. $3 \times 10^{4} \, V\, m^{-1}$

Answer 1

Answer: (B)

Although air is normally an insulator but at a sufficient high voltage, it ionises and become partially conducting.
The electric field at which it occurs is called breakdown field of air and is nearly equal to
$3 \times 10^{6} V / m$