Question

A triode valve has an amplification factor of 20 and its plate is given a potential of 300V. The grid voltage to reduce the plate current to zero, is

A. 25V
B. 15V
C. 12V
D. 10V

Answer 1

We know the amplification factor and we also know the potential of the plate both are given in the question, amplification factor is a ratio so, we have to write the formula for amplification factor then we will have to find the grid potential from that equation after placing all the required values.

Complete answer:
We know that the amplification factor is 20.
We also know that the potential of the plate is 300V.
So according to the formula of amplification factor,
$\text{Amplification factor = }\dfrac{\text{Plate potential}}{\text{Grid potential}}$,
$\text{Grid potential = }\dfrac{\text{Plate potential}}{\text{Amplification factor}}$,
$\text{Grid potential = }\dfrac{\text{300}}{20}$,
So we get the grid potential as 15V.
Therefore the correct option is, option B, 15V.

So, the correct answer is “Option b”.

Additional Information:
When we supply a voltage to the input of the amplifier circuit the voltage is multiplied by the amplification factor and the resultant appears at the output. We can find the amplification factor by dividing the output and input voltage.
A triode is a vacuum tube which amplifies electronic signals, it consists of three electrodes inside a glass envelope, It also consists of a plate which has a voltage of its own, it also has a grid with a voltage of its own and a cathode or heated filament.
A triode and a transistor both have the same features both can amplify a signal in an electrical circuit.

Note:
At first try to look for all the values that are given then try to figure out the formula which will be required to solve the question as per the given values. Students must remember the amplification factor formula to solve the question.