Question

In a vacuum diode, some of the electrons possessing sufficient kinetic energy can reach the plate even if the plate potential is negative. For a certain diode, the plate current becomes zero when plate potential is $- 10V$. What is the kinetic energy of the electronics in $eV$, if the plate potential is $- 4V$?
A. $3eV$
B. $6eV$
C. $4eV$
D. $- 4eV$

Answer 1

To solve this question, we need to understand the relation between the kinetic energy of electrons and the potential difference. Here, we will first find the potential difference by using the given information. After that, we will use the formula for the kinetic energy of the electrons to reach our final answer.

Formula used:
$K.E. = eV$,
where $K.E.$ is the kinetic energy of the electrons, $e$ is the charge of the electrons and $V$ is the potential difference.

Complete step by step answer:
We will first find the value of the potential difference first.We are given that For a certain diode, the plate current becomes zero when plate potential is $- 10V$.And we are asked about the kinetic energy of the electronics in $eV$, if the plate potential is $- 4V$.Therefore, the potential difference is given by subtracting $- 10V$ from $- 4V$.
$- 4 - ( - 10) = - 4 + 10 = 6V$
Now, we will use the formula $K.E. = eV$ to find our answer.
$K.E. = eV$
We have determined that the potential difference value is $6V$ that is $V = 6V$.
$\therefore K.E. = 6eV$

Hence, option B is the right answer.

Note: Here, we have not used the value of $e$ which is the charge of the electron because we are asked to find the kinetic energy of the electronics in $eV$. The value of $e$can be taken as $1.6 \times {10^{ - 19}}C$. Therefore, if we use this value, we can find the required kinetic energy in $V$.