Electromagnetic Spectrum

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CognitoElectromagnetic spectrum — properties and uses

Key facts & equations

EM spectrum properties

All EM waves: travel at the speed of light in a vacuum (3 × 10⁸ m/s).
All are transverse waves. All can travel through a vacuum.
In order of increasing frequency (decreasing wavelength):
Radio → Microwaves → Infrared → Visible → UV → X-rays → Gamma rays.
Higher frequency = higher energy = shorter wavelength.
Wave equation: v = fλ. c = 3 × 10⁸ m/s.

Uses and hazards by type

Radio waves: TV/radio broadcasting, WiFi, communication. Long wavelength, low energy.
Microwaves: mobile phones, satellite communication, microwave ovens. Absorbed by water molecules.
Infrared (IR): thermal imaging, remote controls, optical fibres, heating. All objects emit IR.
Visible light: sight, photography, optical fibres.
UV: sun tanning, sterilisation, detecting fake banknotes. Can damage skin/eyes (sunburn, cancer).
X-rays: medical imaging, security scanners. Ionising — can damage DNA.
Gamma: cancer treatment, sterilisation, PET scans. Highly ionising — most dangerous.

Ionising vs non-ionising radiation

Non-ionising: radio, microwaves, IR, visible. Not enough energy to ionise atoms.
Ionising: UV, X-rays, gamma rays. Enough energy to remove electrons from atoms, damaging DNA.
Microwaves: absorbed by water, causing heating (hence microwave ovens, and concern about mobile phones).
UV: damages skin cells → sunburn → DNA mutations → skin cancer. Ozone layer absorbs UV from Sun.
X-rays pass through soft tissue but are absorbed by dense bone → shadow on image.
Gamma used in radiotherapy: targeted at tumours. Damages cancer cells. High dose would kill all cells.

Exam questions — 4 questions · 11 marks · AQA 8463 style

1 markSpeed of EM wavesAQA 8463 style

What is the speed of all electromagnetic waves in a vacuum?

A 3 × 10⁵ m/s

B 3 × 10⁸ m/s

C 3 × 10¹² m/s

D Different for each type of EM wave

3 marksClassify by ionising abilityAQA 8463 P2 style

Classify radio waves, UV light and gamma rays as ionising or non-ionising. Explain what makes radiation ionising and why this makes it more hazardous. (3 marks)

Hint: Classify each. Define ionising (can remove electrons from atoms). Explain why ionising = more dangerous (damages DNA).

+30 XP

3 marksUses of IR and X-raysAQA 8463 style

Explain how infrared and X-rays are used in medicine. Include how each type of wave interacts with the body. (3 marks)

Hint: IR: emitted by body, detected by camera, or absorbed for heating. X-ray: passes through soft tissue, absorbed by bone — shadow image.

+30 XP

1 markUV hazardAQA 8463 style

Why is UV radiation from the Sun potentially dangerous?

A UV causes objects to heat up rapidly, causing burns

B UV is ionising — it can damage DNA in skin cells, increasing the risk of skin cancer

C UV induces radioactive decay in skin cells

D UV is visible to some animals and disorients human vision

1 markEM orderAQA 8463 style

Which lists EM radiation in order from lowest to highest frequency?

A Gamma, X-rays, UV, visible, IR, microwaves, radio

B Radio, microwaves, IR, visible, UV, X-rays, gamma

C Radio, visible, UV, IR, microwaves, X-rays, gamma

D Microwaves, radio, IR, visible, UV, gamma, X-rays

Electromagnetic Spectrum

EM spectrum properties

Uses and hazards by type

Ionising vs non-ionising radiation

Module complete! 🎉