📖 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.