Question

Which of the following is false with respect to thermionic emission.

• A. At ordinary temperatures, the free electrons of a metal do not have sufficient energy to come out.
• B. When a metal is heated to a high temperature, electrons escape from its surface.
• C. The electrons coming out are called as thermions.
• D. At ordinary temperatures, the free electrons of a metal have sufficient energy to come out.

Answer 1

The correct option is D At ordinary temperatures, the free electrons of a metal have sufficient energy to come out.

Thermionic emission happens when metal is heated, electrons are emitted out.
Normally, at ordinary temperatures, the free electrons of a metal do not have sufficient energy to come out of the surface, so when heated to high temperatures, electrons escape from the metal surface, these are called as thermions.
Hence, $\left(D\right)$ is correct answer.

Why this question? This question tests basic knowledge about thermionic emission.