Generation and Absorption of Electromagnetic Waves

These are opposite energy transfers: absorption increases the atom’s energy, while emission decreases it. Different changes involve different amounts of energy, allowing atoms to absorb and emit waves at different frequencies. Visible light and ultraviolet radiation are examples associated with changes in electron energy levels.

Gamma rays come from the nucleus

Changes can also occur within an atom’s nucleus. Gamma rays originate from changes in the nucleus, rather than from electrons moving between energy levels around it. When the nucleus releases energy in this way, that energy is carried away by a gamma ray.

The important distinction is the location of the change: changes involving electrons occur outside the nucleus; gamma emission involves the nucleus itself.

Producing radio waves with a circuit — Higher Tier only

Radio waves can be generated by oscillations in an electrical circuit. An oscillation is a repeated change or back-and-forth movement. In an alternating-current circuit, the current repeatedly reverses direction, so electric charge moves back and forth rather than continuously in one direction.

A transmitting aerial, also called an antenna, can be connected to a high-frequency alternating-current source. Charge oscillates up and down the aerial, producing radio waves that travel away from it. The radio waves have the same frequency as the oscillations in the transmitting circuit.

Frequency means the number of complete oscillations each second. Faster oscillations in the circuit therefore produce higher-frequency radio waves. Energy supplied to the transmitting circuit is transferred outwards by the waves.

Receiving radio waves — Higher Tier only

A receiving aerial can absorb energy from incoming radio waves. This can cause charge in the aerial to oscillate, creating an alternating current with the same frequency as the absorbed radio wave. Radio waves can therefore induce oscillations in an electrical circuit.

Transmission and reception form a linked sequence: electrical oscillations produce a radio wave, and absorption of that wave can produce electrical oscillations elsewhere. Energy travels between the aerials in the electromagnetic wave; the charge in the transmitting aerial does not travel across the gap to the receiver.

This connection between circuits and electromagnetic waves makes radio communication possible: a transmitting circuit sends energy out as waves, and a receiving circuit responds when those waves are absorbed.

• Changes in atoms and their nuclei can generate or absorb electromagnetic waves over a wide frequency range.
• Electron gains energy: moves to a higher energy level by absorption.
• Electron loses energy: moves to a lower energy level and emits an electromagnetic wave.
• Gamma rays originate from changes in the nucleus.

Radio waves — Higher Tier only

• Oscillating charge in an electrical circuit produces radio waves.
• Absorbed radio waves may induce an alternating current in a receiving circuit.
• Transmitting oscillations → radio wave → receiving alternating current: all have the same frequency.