What is thermionic emission?

Thermionic emission is the release of electrons from a metal surface when the metal is heated to a sufficiently high temperature.

Where are electrons released from during thermionic emission?

Electrons are emitted from the surface of the metal.

During thermionic emission, what happens to the thermal energy supplied to the metal?

Thermal energy is transferred to the conduction electrons in the metal.

What change occurs in the electrons when a metal is heated during thermionic emission?

The electrons gain kinetic energy.

State the formula for the work done on an electron when it is accelerated through a potential difference V.

W = eV, where W is the work done, e is the electron charge, and V is the potential difference.

What does the product eV represent when an electron is accelerated through a potential difference?

It represents the work done on the electron by the electric field, equal to the charge multiplied by the potential difference.

AQA A-Level Physics 7408

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Turning Points in Physics

Thermionic emission of electrons

3 things to know
Paper 3, section B

Overview

Releasing electrons from a heated metal, and the work done accelerating them through a potential difference.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

What happens to electrons when a metal is heated, and how is work on an electron calculated?

Numbers

How is v = √(2eV/m) derived, and what must an electron overcome to escape?

Key term

Which electrons in a heated metal are able to escape during thermionic emission?

Questions from this subtopic

Each one with the model answer underneath.

1
What is thermionic emission?
Model answer
Thermionic emission is the release of electrons from a metal surface when the metal is heated to a sufficiently high temperature.
2
Where are electrons released from during thermionic emission?
Model answer
Electrons are emitted from the surface of the metal.
3
During thermionic emission, what happens to the thermal energy supplied to the metal?
Model answer
Thermal energy is transferred to the conduction electrons in the metal.
4
What change occurs in the electrons when a metal is heated during thermionic emission?
Model answer
The electrons gain kinetic energy.
5
State the formula for the work done on an electron when it is accelerated through a potential difference V.
Model answer
W = eV, where W is the work done, e is the electron charge, and V is the potential difference.
6
What does the product eV represent when an electron is accelerated through a potential difference?
Model answer
It represents the work done on the electron by the electric field, equal to the charge multiplied by the potential difference.

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