Coating of strontium oxide on a tungsten cathode in a valve is good for thermionic emission because:

Why is a vacuum tube called a valve in electronics?

The plate resistance of two triode valves is $2 \, k\Omega$ and $4 \, k\Omega$. The amplification factor of each valve is $40$. The ratio of voltage amplification,when used with a $4 \, k\Omega$ load resistance,will be:

The amplification factor of a triode valve is $15$. If the grid voltage is changed by $0.3 \,V$,what is the change in plate voltage required to keep the plate current constant (in $V$)?

In a triode valve,the amplification factor is $20$ and the mutual conductance is $10^{-3} \text{ mho}$. The plate resistance is:

In the grid circuit of a triode, an input voltage $E = 2\sqrt{2} \cos \omega t$ is applied. If the amplification factor $\mu = 14$ and the plate resistance $r_p = 10 \text{ k}\Omega$, find the $r.m.s.$ current flowing through the load resistance $R_L = 12 \text{ k}\Omega$ in $\text{mA}$.