What is the photoelectric effect?

The photoelectric effect is the emission of electrons from the surface of a metal when electromagnetic radiation of a high enough frequency falls on it.

What is observed when radiation below a certain frequency is shone on a metal, however intense it is?

No electrons are emitted at all, no matter how bright the source or how long it is left shining.

How does the maximum kinetic energy of the emitted electrons depend on the frequency and on the intensity of the radiation?

It increases as the frequency increases but is completely unaffected by the intensity of the radiation.

How does the rate of emission of photoelectrons depend on the intensity of the radiation?

Above the threshold frequency the number of electrons emitted per second is directly proportional to the intensity, because a brighter beam delivers more photons per second.

CCEA A-Level Physics 1210

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Quantum Physics

The photoelectric effect

3 things to know
Unit AS 2

Overview

Photoelectric effect and one-to-one interaction between photon and electron.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Use the photon model to explain why increasing the intensity increases the number of electrons emitted each second.

Key term

Describe a demonstration of the photoelectric effect using a zinc plate and a gold-leaf electroscope.

Key term

How quickly does emission begin once light of a suitable frequency reaches a metal surface?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the photoelectric effect?
Model answer
The photoelectric effect is the emission of electrons from the surface of a metal when electromagnetic radiation of a high enough frequency falls on it.
2
Describe a demonstration of the photoelectric effect using a zinc plate and a gold-leaf electroscope.
Model answer
A clean zinc plate is placed on a negatively charged gold-leaf electroscope, and when ultraviolet radiation shines on the plate the leaf falls, showing that negative charge is leaving the metal as electrons are emitted.
3
How quickly does emission begin once light of a suitable frequency reaches a metal surface?
Model answer
Emission begins immediately, with no measurable delay, even when the radiation is extremely faint.
4
What is observed when radiation below a certain frequency is shone on a metal, however intense it is?
Model answer
No electrons are emitted at all, no matter how bright the source or how long it is left shining.
5
How does the maximum kinetic energy of the emitted electrons depend on the frequency and on the intensity of the radiation?
Model answer
It increases as the frequency increases but is completely unaffected by the intensity of the radiation.
6
How does the rate of emission of photoelectrons depend on the intensity of the radiation?
Model answer
Above the threshold frequency the number of electrons emitted per second is directly proportional to the intensity, because a brighter beam delivers more photons per second.

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