Properties of Electromagnetic Waves 2 and Hazards | Physics

📖 In-Depth Theory

Hazards of EM Radiation

Not all EM radiation is harmful — hazard depends on frequency (and therefore energy per photon).

HIGHER FREQUENCY = MORE ENERGY = MORE POTENTIALLY HARMFUL.

RADIO WAVES AND MICROWAVES:

Generally low risk at normal exposures.

Microwaves CAN heat tissue (same mechanism as microwave oven — absorbed by water).

Concerns about mobile phones (microwaves) have been studied — no confirmed harmful effects at normal levels.

INFRARED:

Absorbed by skin — can cause BURNS at high intensity.

Thermal cameras detect infrared emitted by people and objects.

VISIBLE LIGHT:

Normally safe. Very intense visible light can damage retina (e.g. looking at solar eclipse or high-power laser).

Ultraviolet, X-rays and Gamma Rays

ULTRAVIOLET (UV):

Can cause SUNBURN — damages skin cells.

Increases risk of SKIN CANCER — damages DNA in skin cells.

Can cause damage to EYES — cataracts, photokeratitis ('snow blindness').

Protection: sunscreen (absorbs UV), sunglasses (filter UV), protective clothing.

X-RAYS:

Penetrate soft tissue, absorbed by denser materials (bone, metal).

Used in medical imaging (X-rays, CT scans).

Can IONISE cells — damage DNA → cancer risk.

Dose kept minimal; radiographers leave the room; lead aprons used.

GAMMA RAYS:

Highest energy — most penetrating, most ionising.

Emitted by radioactive materials.

Can cause radiation sickness at high doses, cancer at lower doses.

Used in cancer TREATMENT (radiotherapy) — beams focused on tumour.

Ionising radiation (UV, X-ray, gamma): damages DNA → mutations → cancer.

Radio Waves — Production and Uses

RADIO WAVES are produced by OSCILLATING ELECTRICAL CIRCUITS:

An alternating current at radio frequency in a transmitter aerial causes oscillating charges → emit radio waves.

Frequency of radio waves = frequency of electrical oscillation in the circuit.

ABSORPTION OF RADIO WAVES:

When radio waves are absorbed by a conducting aerial → induces an alternating current at the SAME FREQUENCY as the radio wave → this is how radio receivers work.

DIFFERENT EM WAVES — INTERACTION WITH MATTER SUMMARY:

Absorbed: energy transferred to medium (heating or other effects).

Transmitted: passes through without significant interaction.

Reflected: bounces off boundary.

Refracted: changes direction at boundary due to speed change.

The interaction depends on the wavelength and the material's properties.

⚠️ Common Mistake

UV, X-rays and gamma rays are all IONISING — they can damage DNA. Infrared and visible light can cause burns/eye damage but are NOT ionising. The hazard from ionising radiation is cancer and cell damage — not just burns.

📌 Key Note

Hazards increase with frequency. Infrared: burns. UV: sunburn, skin cancer, eye damage. X-rays: ionising, cancer risk, medical imaging. Gamma: most ionising, cancer/radiotherapy. Radio waves: produced by oscillating circuits, absorbed to induce same-frequency AC. Ionising radiation damages DNA → mutations.

🎯 Matching Activity — EM Wave Hazards

Match each EM wave type to its main hazard and protection. — drag the symbols on the right to match the component names on the left.

Infrared

Drop here

Ultraviolet

Drop here

X-rays

Drop here

Gamma rays

Drop here

Sunburn and skin cancer — DNA damage in skin cells — use sunscreen and cover up

Ionising — DNA damage and cancer risk — minimise dose, use lead shielding

Most ionising and penetrating — used in radiotherapy — needs lead/concrete shielding

Thermal burns at high intensity — avoid prolonged exposure to intense sources

🎯 Test Yourself

Question 1 of 2

1. Why are X-rays more harmful to living tissue than infrared radiation of the same intensity?

2. A person sunbathes without sunscreen. Which part of sunlight causes the most DNA damage?

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⚡ Properties of Electromagnetic Waves 2 and Hazards

Hazards of EM Radiation

Ultraviolet, X-rays and Gamma Rays

Radio Waves — Production and Uses

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