Waves — properties, types and the electromagnetic spectrum

What is a wave?

A wave is a transfer of energy without a net transfer of matter. The particles (or fields) oscillate but do not travel with the wave.

Key wave terms

Amplitude: maximum displacement of a particle from the equilibrium (rest) position. Larger amplitude = more energy.

Wavelength (λ): distance from one point on a wave to the next identical point (e.g. crest to crest). Measured in metres (m).

Frequency (f): number of complete waves passing a point per second. Measured in hertz (Hz). 1 Hz = 1 wave per second.

Wave speed (v): how fast the wave travels. Measured in m/s.

The wave speed equation: v = f × λ (speed = frequency × wavelength)

Example: sound wave at 340 m/s with frequency 680 Hz: λ = v/f = 340/680 = 0.5 m

Transverse vs longitudinal waves

Reflection

Angle of incidence = angle of reflection (measured from the normal).

Normal = imaginary line perpendicular to the surface at the point of incidence.

Refraction

Refraction is the change in direction when a wave enters a new medium and changes speed.

Light refracts at the boundary between air and glass:

• Going from air to glass: slows down → bends towards the normal.
• Going from glass to air: speeds up → bends away from the normal.

Snell's Law (Higher): n = sin(i)/sin(r), where n is the refractive index, i is the angle of incidence, r is the angle of refraction.

The electromagnetic spectrum

All EM waves travel at 3 × 10⁸ m/s in a vacuum. They are transverse waves.

Increasing wavelength / decreasing frequency: GAMMA → X-RAY → ULTRAVIOLET → VISIBLE LIGHT → INFRARED → MICROWAVES → RADIO WAVES