Every wave concept you need — transverse, longitudinal, EM spectrum, refraction, lenses — interactive, visual, and with just enough humour to stay awake.
AQA / Edexcel · Exam in a week? Ride the wave.A wave transfers energy without transferring matter. The medium oscillates; the energy moves on.
Oscillation is perpendicular to direction of travel. Like a rope being flicked — particles move up and down, wave moves left to right.
Examples: light, water ripples, microwaves, seismic S-waves
Oscillation is parallel to direction of travel. Like a slinky — particles bunch together (compression) then spread out (rarefaction).
Examples: sound, ultrasound, seismic P-waves
Amplitude, wavelength, frequency, period — the four numbers that define any wave.
The single most important wave equation. Three quantities, three rearrangements.
Speed of light: v = 3×10⁸ m/s | Frequency: f = 5×10¹⁴ Hz
λ = v ÷ f = 3×10⁸ ÷ 5×10¹⁴ = 6×10⁻⁷ m = 600 nm (orange-red visible light)
Angle of incidence = angle of reflection. Both measured from the normal. Always.
The angle of incidence always equals the angle of reflection. Both angles are measured from the normal — an imaginary line perpendicular to the surface.
Concave mirrors converge parallel rays to a focal point — used in torches and telescopes.
Convex mirrors diverge rays — used as car wing mirrors for a wide field of view.
Waves change speed when they enter a new medium — and if they hit at an angle, they bend.
Into a denser medium (e.g. air→glass): wave slows down, bends toward the normal.
Into a less dense medium (glass→air): wave speeds up, bends away from the normal.
n = refractive index. The higher the refractive index, the more a medium slows light down and bends it toward the normal.
Seven types of EM wave — all travel at 3×10⁸ m/s in a vacuum. Click a region to explore.
Click a region above to see details about that part of the EM spectrum.
Radio → Micro → Infrared → Visible → UV → X-ray → Gamma
Raging Martians Invaded Venus Using X-ray Guns
Longitudinal mechanical waves that need a medium to travel. No medium, no sound.
| Medium | Speed | Why? |
|---|---|---|
| Air (20°C) | ~340 m/s | Particles are far apart — slow to transfer energy |
| Water | ~1,500 m/s | Denser — particles transfer energy faster |
| Steel | ~5,000 m/s | Very stiff — vibrations travel quickly |
Ultrasound is above 20,000 Hz — too high-pitched for human hearing. Pulse-echo timing gives distance: d = v × t ÷ 2
Lenses refract light to converge or diverge rays. Three key rays explain every lens diagram.
Where rays converge = real image. Where extensions back-project to = virtual image.
Earthquakes send waves through Earth — and those waves reveal what's inside.
• S-waves create a shadow zone on the far side of Earth → proves the outer core is liquid
• P-waves refract at boundaries → reveals layers of different density (crust, mantle, outer core, inner core)
• The inner core is believed to be solid iron-nickel — P-waves can pass through it but travel faster there
Five questions. No cheating. The equations panel is right there though, which is very forgiving of it.
1. A wave has frequency 5 Hz and wavelength 20 m. What is its speed?
2. Which type of wave has oscillations perpendicular to the direction of travel?
3. A ray of light hits a flat mirror at 35° to the normal. What is the angle of reflection?
4. Which ordering correctly goes from lowest frequency to highest?
5. A wave has a period of 0.04 s. What is its frequency?
v = f × λWave speed = frequency × wavelengthT = 1 / fPeriod = 1 / frequencyf = 1 / TFrequency = 1 / periodn = sin(i) / sin(r)Snell's Law — refractive indexd = v × t / 2Ultrasound echo distancec = 3 × 10⁸ m/sSpeed of light in vacuum