Characteristics of Vacuum Diode

In a vacuum diode, a large number of free electrons are emitted from the _____?

Is a vacuum tube a diode?
 

In a vacuum diode, a large number of free electrons are emitted from the cathode which builds up at one place near the cathode and forms a cloud of free____________________________?

Vacuum diode is an electronic device that allows the electric current in _____ .(cathode to anode) and blocks the electric current in another direction (anode to cathode).

It consists of a vacuum container with cathode and anode inside. 

Describe the saturation region in vaccum diode characteristics?

What are characteristics of vacuum tube?
 

What is Child$\text{'}$s law?

Under space charge limited condition, the plate current of a diode increases with the increase in plate potential.

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 $\mathrm{V}$.)