Electromagnetic Spectrum

Definition

The full range of electromagnetic waves arranged in order of wavelength and frequency, from low-frequency radio waves to high-frequency gamma rays, all travelling at the speed of light in vacuum.

Key points

• Order from longest wavelength (lowest frequency) to shortest wavelength (highest frequency): radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
• All electromagnetic waves travel at about 3 lakh kilometres per second (3 times 10 to the power 8 metres per second) in vacuum; energy rises with frequency.
• Visible light is a thin band the eye can see, ranging roughly from violet (shorter wavelength) to red (longer wavelength), remembered as VIBGYOR.
• Uses: radio and TV broadcasting (radio waves), mobile and radar and cooking (microwaves), remote controls and thermal imaging (infrared), sterilisation (ultraviolet), medical imaging and security scanning (X-rays), and cancer treatment (gamma rays).
• Higher-energy rays (ultraviolet, X-rays, gamma rays) are ionising and can damage living tissue, which is why exposure is controlled.

Why it matters for CAPF

The order of the spectrum, the constant speed of light, VIBGYOR, and the uses of each band (radar, X-ray scanning, infrared imaging) are standard physics facts with direct surveillance and security applications.

Common confusion

All electromagnetic waves move at the same speed in vacuum; they differ in wavelength and frequency, not speed. Microwaves are not the same as radio waves even though both are long-wavelength; X-rays and gamma rays differ in their source (X-rays from electron transitions, gamma rays from the nucleus).

Related concepts

concept doppler effect, concept radioactivity, concept lasers

Parent note

physics everyday