Is a vacuum tube a diode?
 

The space charge limited current in a diode is $2 \mathrm{mA}$ at $20 \mathrm{V}.$ At what voltage its value will be $16 \mathrm{mA}.$

Correct the following sentence:

The space charge limited current varies directly as the square root of plate current.

The space charge limited current in a diode is $16 \mathrm{mA}$ at $80 \mathrm{V}.$ At what voltage its value will be $128 \mathrm{mA}.$ (Write the numerical answer in terms of $\mathrm{V}$.)