P3.3P3. Waves

Electromagnetic spectrum — Combined Science 0653 - Physics Revision Notes & Topical Questions

5 min read 10 parts Lesson 7 of 9 1 quiz

📚 Combined Science 0653 - Physics Hub / Topical Revision

0%read

Lesson summary

P3.3 Electromagnetic spectrum — COMBINED SCIENCE notes: Describe the properties, uses and dangers of each region of the electromagnetic spectrum and their use in communications.Electromagnetic (EM) waves = transverse waves that transfer energy from a source to an absorber.Speed —…

Wave equation
From longest to shortest wavelength
Visible light
Memory aid
Radio waves
Microwaves

Part 1 of 8Electromagnetic waves

Electromagnetic waves

Electromagnetic (EM) waves

Electromagnetic (EM) waves transverse waves that transfer energy from a source to an absorber.

Speed

Speed all EM waves travel at the same speed in a vacuum, 3.0 × 10⁸ m/s, and at about the same speed in air.

Wave equation

Wave equation c = f × λ, so a long wavelength means a low frequency.

Vacuum

EM waves can travel through a vacuum.

Energy

Energy the energy of the waves increases as the frequency increases.

Part 2 of 8Order of the spectrum

1From longest to shortest wavelength

From longest to shortest wavelength radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.

2Frequency

Frequency it increases in the same order, from radio waves to gamma rays.

3Visible light

Visible light red, orange, yellow, green, blue, indigo, violet, with red at the long-wavelength end.

4Memory aid

Raging Martians Invaded Venus Using X-ray Guns.

Part 3 of 8Uses of radio waves, microwaves and infrared

Radio waves

Radio waves radio and television broadcasting, astronomy, and radio frequency identification (RFID).

Microwaves

Microwaves satellite television, mobile phones, Wi-Fi and radar, and microwave ovens that heat food at high intensity.

Infrared

Infrared electric grills, remote controls, intruder alarms and thermal imaging cameras.
Optical fibres carry infrared more efficiently than visible light.

Part 4 of 8Uses of visible light, ultraviolet, X-rays and gamma rays

Visible light

Visible light vision, photography, videography and illumination.

Ultraviolet

Ultraviolet fluorescence, where substances absorb UV and re-emit visible light.
It is used in security marking with special ink, on bank notes and in fluorescent lamps.

X-rays

X-rays medical imaging, because they pass through soft tissue but are absorbed by dense bone.

Gamma rays

Gamma rays killing cells for cancer detection and treatment, and sterilising food, water and medical equipment.

Part 5 of 8Dangers of electromagnetic waves

Wave	Danger
Radio	No known danger
Microwaves	Internal heating of body cells
Infrared	Skin burns
Ultraviolet	Damage to surface cells and eyes, leading to skin cancer and eye conditions
X-rays and gamma rays	Mutation or damage to cells, which can cause cancer

Ionising radiation

Ionising radiation ultraviolet, X-rays and gamma rays have enough energy to ionise atoms, and the higher the frequency the more ionising they are.

Protection

Protection sunscreen and good sunglasses absorb ultraviolet.

Microwave ovens

Microwave ovens metal walls and a metal grid in the door stop the microwaves escaping.

Part 6 of 8Communication with satellites

Microwaves

Microwaves satellites use microwaves because they are not refracted, reflected or absorbed by the atmosphere or ionosphere.

Geostationary satellite

Geostationary satellite it orbits above the equator at about 36 000 km with a period of 24 hours, so it stays above the same point.
It is used for broadcasting, satellite television and some satellite phones.

Low-orbit satellite

Low-orbit satellite it orbits at about 200 km, giving a shorter signal delay and clearer images.
It is used for weather monitoring, military use and imaging, but several satellites are needed for continuous cover.

Polar orbit

Polar orbit a low orbit that passes over the poles.

Part 7 of 8Communication systems

Communication systems

Mobile phones and Wi-Fi

Mobile phones and Wi-Fi they use microwaves, which pass through most walls and need only a short aerial.
Transmitter masts must not be spaced so far apart that hills or the curvature of the Earth block the signal.

Radio waves

Radio waves they have wavelengths of about a kilometre and diffract around hills.

Bluetooth

Bluetooth it uses short-wavelength radio waves for high data rates over short distances, and the signal is weakened passing through walls.

Optical fibres

Optical fibres they use visible light or infrared, which carry high data rates because of their high frequency.

Part 8 of 8Analogue and digital signals

1Analogue signal

Analogue signal it varies continuously and can take any value.

2Digital signal

Digital signal it takes only two values, such as 1 and 0 or high and low.

3Sending sound

Sending sound an analogue signal is converted to digital before transmission and back to analogue after reception.

4Advantages of digital signals

Advantages of digital signals they can be regenerated with minimal noise, travel further, carry data faster, and carry extra data for error checking.

Key terms

Term	Meaning
Electromagnetic wave	A transverse wave that transfers energy and can travel through a vacuum.
Ionising radiation	Radiation with enough energy to remove electrons from atoms.
Fluorescence	Absorbing ultraviolet radiation and re-emitting it as visible light.
Geostationary orbit	An orbit at about 36 000 km above the equator with a period of 24 hours.
Analogue signal	A signal that varies continuously.
Digital signal	A signal with only two possible values.
Microwave	Electromagnetic radiation between radio waves and infrared.

Avoid these mistakes

Saying EM waves need a medium — they travel through a vacuum.

Saying gamma rays have the longest wavelength — they have the shortest wavelength and the highest frequency.

Saying microwaves are ionising — only ultraviolet, X-rays and gamma rays are ionising.

Saying all EM waves have the same speed in all materials — they have the same speed in a vacuum.

Saying X-rays are absorbed by soft tissue — they pass through soft tissue and are absorbed by bone.

Last updated: 12 October 2026