3.2.2.1
The photoelectric effect shows light behaves as particles
The Photoelectric Effect — AQA A-Level Physics
Key Definition
Photoelectric effect — The emission of electrons from the surface of a metal when electromagnetic radiation of sufficiently high frequency is incident on it.
$$hf = \phi + E_{k(max)}$$
- Electrons emitted this way are called photoelectrons.
- Each electron absorbs only a single photonA quantum (discrete packet) of electromagnetic radiation. Its energy is proportional to its frequency.. This is evidence that light is quantisedExisting only in discrete values. ChargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). is quantised because it can only exist as whole-number multiples of the elementary chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). e..
- Only frequencies above a threshold frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz).The minimum frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). of incident radiation required to cause photoelectric emission from a particular metal surface. cause emission — increasing intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. below this threshold has no effect.
- A wave model of light cannot explain this. Waves should transfer energyThe capacity to do work. Measured in joules (J). gradually, so any frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). should eventually eject electrons.
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