How materials and circuits interact with EM waves

Higher tier: different materials absorb, transmit, reflect or refract EM waves depending on wavelength. Radio waves can be made and detected by electrical circuits, and atoms and nuclei can emit and absorb radiation.

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Materials and wavelength

Whether a material absorbs, transmits, reflects or refracts an EM wave depends on the material and the wavelength.
Examples: ordinary glass transmits visible light but absorbs much of the ultraviolet; water absorbs microwaves strongly (which is how a microwave oven heats food); X-rays pass through soft tissue but are absorbed by bone; the upper atmosphere reflects some radio waves.

Radio waves and circuits

An alternating current in a transmitter aerial makes the electrons oscillate, and this produces radio waves of the same frequency.
When radio waves are absorbed by a receiving aerial (a conductor), they make the electrons in it oscillate, inducing an alternating current with the same frequency as the waves. This is how radios and TVs receive signals.

Atoms and nuclei

When an electron in an atom absorbs EM radiation of the right energy, it moves to a higher energy level (further from the nucleus). When it drops back, it emits EM radiation (such as visible light or ultraviolet).
Changes in the nucleus can produce gamma rays.
Worked example

A radio station transmits at 100 MHz. What is the frequency of the alternating current induced in a receiving aerial?

  1. The absorbed radio waves make electrons in the aerial oscillate.
  2. The induced current has the same frequency as the waves.

Answer: 100 MHz

Key idea

Absorption, transmission, reflection and refraction depend on wavelength and material. An a.c. in an aerial produces radio waves of the same frequency; absorbed radio waves induce an a.c. of the same frequency. Electrons moving between energy levels absorb or emit EM radiation; nuclear changes produce gamma rays.

Key words
Wavelength
The distance from one point on a wave to the same point on the next wave, for example crest to crest.
Refraction
A change in direction of a wave when it crosses a boundary at an angle, caused by a change in speed.
Frequency
The number of waves passing a point each second. Unit hertz (Hz). f = 1 ÷ T.
Current
The rate of flow of charge. Unit ampere (A).

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  1. An aerial absorbs radio waves of frequency 100 MHz. What is induced in the aerial?

    1. A direct current
    2. An alternating current of frequency 50 Hz
    3. Nothing
    4. An alternating current of frequency 100 MHz
    Show the answer

    Answer: An alternating current of frequency 100 MHz

    Radio waves make electrons in the aerial oscillate at the wave's frequency.

  2. A transmitter aerial has an alternating current of 800 kHz. What frequency are the radio waves it produces?

    1. 1600 kHz
    2. 800 kHz
    3. 50 Hz
    4. 400 kHz
    Show the answer

    Answer: 800 kHz

    Oscillating electrons produce radio waves at the same frequency.

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Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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