5.1 & 5.2 The Photoelectric Effect

Photons

Packets of radiation with energy proportional to their frequency and INVERSELY proportional to wavelength

Equations to find E

E = hf and E = hc/λ

What is the value of h?

6.63 x 10^-34 Js

What do we measure energy of a photon in?

Joules

The Photoelectric Effect

The photoelectric effect is when light above a particular frequency hits a metal surface, causing electrons to be emitted from the surface.

When are electrons emitted from a surface?

Electrons are only emitted from. surface if the light is above the threshold frequency

What happens when you increase intensity of light?

Maximum kinetic energy remains the same

The number of photoelectrons emitted increases

Define a one to one interaction.

One photon can cause the emission of ONE electron.

Photoelectric Effect and Particle Theory

The photoelectric effect shows that light behaves as particles (photons). Only light above a certain frequency can eject electrons from a metal, no matter how bright the light is.This can't be explained by wave theory, but it supports the idea that light delivers energy in packets (photons) instead of sustained oscillations, proving its particle-like behaviour.

Threshold Frequency

The lowest frequency of light that causes electrons to be emitted from the surface of a metal

Work Function

Minimum amount of energy needed to release an electron from the surface of a metal

Threshold frequency equation

f = Φ / h

Calculating maximum photoelectric energy

E = hf - Φ

This can also be expressed as:

1/2mv^2 = hf - Φ

Converting ev to J

Multiply by 1.6 x 10^-19 (elementary charge)

the number should get smaller

Converting J to eV

Divide by 1.6 x10^-19 (elementary charge)

The number should get bigger