Waves
What's covered
Key facts
In order of increasing frequency: radio, microwave, IR, visible, UV, X-ray, gamma.
Angles of incidence, reflection, and refraction are all measured from the normal to the ray.
P-waves (primary waves) are longitudinal seismic waves: particles vibrate parallel to the direction of wave travel.
In the ear, the eardrum (tympanic membrane) converts incoming sound waves into mechanical vibrations that are then passed to the inner ear.
Total internal reflection happens when the angle of incidence exceeds the critical angle.
Light is an example of a transverse wave: electric and magnetic fields oscillate perpendicular to the direction of propagation.
Ultrasound has a frequency above 20 000 Hz (20 kHz) — above the upper limit of human hearing.
Fibre-optic broadband cables use visible light.
Amplitude is the maximum displacement of a particle from its rest (equilibrium) position.
Period T of a wave is the time for one wave to pass. Frequency f = 1 / T.
Sample questions
A taste of the 124 questions in this topic — answers marked. Sign up to practise the full set with spaced repetition.
Which list orders the EM spectrum from longest to shortest wavelength?
- •Gamma, X-ray, UV, visible, IR, microwave, radio
- •IR, radio, microwave, visible, UV, gamma, X-ray
- ✓Radio, microwave, IR, visible, UV, X-ray, gamma
- •Radio, microwave, visible, IR, UV, X-ray, gamma
Why does light bend (refract) when entering glass?
- •Frequency drops on entering glass
- •Glass repels light particles
- ✓It slows down when entering a denser medium
- •It speeds up in denser materials
What is the difference between P-waves and S-waves in earthquakes?
- •Both P- and S-waves are longitudinal but P-waves have higher amplitude in solids
- •P- and S-waves both travel through solids and liquids, only at different speeds
- ✓P-waves are longitudinal; S-waves are transverse and only travel through solids
- •P-waves are transverse and travel only through solids; S-waves are longitudinal
Why is sound classified as a longitudinal wave?
- •Compressions are peaks of high amplitude and rarefactions are troughs of zero
- •It is transverse because air particles vibrate at right angles to the wave
- ✓Particles vibrate parallel to the direction of energy transfer
- •Sound creates longitudinal waves in a vacuum and pushes electrons forward
What is total internal reflection?
- •All colours of white light reflect equally from a prism's surface
- •Light passes straight through a glass block without bending at either surface
- ✓Light reflects fully back when incidence exceeds the critical angle
- •UV light reflects off a metallic surface with 100% efficiency
What is the difference between a transverse and a longitudinal wave?
- •In transverse waves, energy travels faster because particles move at right angles
- •Transverse waves only travel through a vacuum; longitudinal waves need a medium
- •Transverse waves only travel through solids; longitudinal waves through fluids only
- ✓Transverse: vibrations perpendicular to wave travel (e.g. light)
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