Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P3.1 — General properties of waves (Part (a))
• Topic P3.2.1 — Reflection of light (Part (b))
• Topic P3.1 — Wave equation (Part (c))
• Topic P3.2.4 — Dispersion of light (Part (d))
(a)(i) Perpendicular / at right angles / at 90°
In a transverse wave, the direction of vibration is perpendicular to the direction of propagation (energy transfer).
(a)(ii) Transverse waves: ultraviolet, visible light, water wave
Seismic P-waves and sound waves are longitudinal waves.
(b)(i) Ray diagram for plane mirror reflection:
1. Draw two rays from point X to the mirror.
2. At each point of incidence, draw the normal and apply the law of reflection (angle of incidence = angle of reflection).
3. Extend the reflected rays behind the mirror using dashed lines.
4. The point where the dashed lines meet is the virtual image (Y).
(b)(ii) Properties: upright, virtual
Plane mirror images are virtual (cannot be projected on a screen), upright (same orientation as object), same size as object, and laterally inverted.
(c) Wavelength calculation:
v = fλ
λ = v/f = (3.0 × 10⁸) / (6.6 × 10¹⁴) = 4.5 × 10⁻⁷ m
(d) Dispersion in terms of wave frequency:
• Different colours of light have different frequencies.
• As white light enters a prism, each colour refracts by a different amount.
• Higher frequency (violet) light is refracted more than lower frequency (red) light.
• This separates the colours, producing the visible spectrum.
