📖 In-Depth Theory
Wave Front Diagrams
A WAVE FRONT is an imaginary line connecting all points of a wave that are at the same phase (e.g. all the crests).
Wave fronts are PERPENDICULAR to the direction of wave travel.
For PLANE WAVES (parallel wave fronts):
All points move in the same direction.
Shown as parallel lines with arrows indicating direction of travel.
For CIRCULAR WAVES (from a point source):
Wave fronts are concentric circles spreading outward.
Frequency and wavelength shown by spacing between lines.
CLOSER WAVE FRONTS: shorter wavelength or wave fronts bunching up as wave slows.
FURTHER APART: longer wavelength or wave fronts spreading as wave speeds up.
REFRACTION using wave fronts:
When a wave crosses into a new medium, speed changes.
Part of the wave front enters the new medium first → that part slows (or speeds up) first.
The wave front pivots → wave changes direction.
Explaining Refraction with Wave Fronts
WHY REFRACTION OCCURS:
At a boundary, the wave speed changes.
If wave slows: wave fronts bunch together (shorter wavelength), wave turns towards the normal.
If wave speeds up: wave fronts spread apart (longer wavelength), wave turns away from the normal.
FREQUENCY DOESN'T CHANGE during refraction — only speed and wavelength change.
v = fλ → if v decreases and f stays constant → λ decreases.
EXAMPLE — Light entering glass:
Light travels slower in glass than air.
Wave front entering glass slows down → bends towards the normal.
Wavelength shortens inside glass.
Frequency unchanged — the eye perceives the same colour.
SEISMIC WAVE REFRACTION:
P-waves travel faster in denser rock.
As P-waves descend through Earth, density increases → speed increases → waves curve upward.
This is why P-waves travel in curved paths through the Earth.
Radio Waves and Electrical Circuits
RADIO WAVES can be PRODUCED by oscillations in electrical circuits.
An oscillating current in an aerial (antenna) produces oscillating electromagnetic field → radio wave emitted.
Frequency of radio wave = frequency of electrical oscillation.
RADIO WAVE ABSORPTION AND CURRENT INDUCTION:
When a radio wave is ABSORBED by a conductor (receiving aerial):
The oscillating electromagnetic field drives electrons in the conductor.
An ALTERNATING CURRENT (AC) is induced with the SAME FREQUENCY as the radio wave.
This is the basis of all radio and wireless communication receivers.
REFRACTION OF RADIO WAVES:
Radio waves refract in the ionosphere (upper atmosphere).
This allows long-distance communication — waves bent back to Earth's surface.
Different frequencies refract differently — some pass through, some are reflected.
⚠️ Common Mistake
During refraction, FREQUENCY stays constant — only SPEED and WAVELENGTH change. v = fλ, so if v decreases and f is constant, λ must decrease proportionally. Wave fronts are perpendicular to the direction of travel — closer wave fronts = shorter wavelength, not higher frequency.