BRAINCAKEWaves in matter
Revision notes for Waves in matter in OCR Physics A (J249). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- Wave motion: amplitude, wavelength, frequency and periodA wave transfers energy from one place to another without transferring matter.
- Wavelength and frequencyThe wavelength of a wave is the distance from a point on one wave to the same point on the next wave.
- The wave speed equationThe wave speed is the distance a wave travels each second.
- Calculations with wave speed, frequency and wavelengthTo use the wave equation, wave speed (m/s) = frequency (Hz) × wavelength (m), first check the units.
- Transverse and longitudinal wavesWaves are described by the direction of vibration compared with the direction of travel.
- Waves changing medium: speed, frequency and wavelengthWhen a sound wave passes from one medium into another, its frequency stays the same.
- Reflection, transmission and absorption of wavesWhen a wave reaches the boundary between two materials, called an interface, three things can happen.
- Sound waves and vibrations in solidsA sound wave in air is a series of vibrations of the air.
- Limits of hearing and hearing changes with ageThe ear can only detect sound over a limited frequency range.
- Transverse and longitudinal waves and measuring wave speedRipples on the surface of water are used to model transverse waves.
- Evidence that the wave travels, not the mediumA wave transfers energy from one place to another, but it does not transfer matter.
- Electromagnetic waves are transverse and travel through spaceElectromagnetic waves are transverse waves: the oscillations are at right angles to the direction the wave travels.
- Energy transfer by electromagnetic wavesElectromagnetic waves transfer energy from a source to an absorber.
- Frequency and wavelength across the spectrumAll electromagnetic waves obey the wave equation: wave speed = frequency × wavelength, or v = f × wavelength.
- The groups of the electromagnetic spectrumThe electromagnetic spectrum is a continuous family of waves split into seven main groups.
- What our eyes can detectOur eyes can only detect a limited range of the electromagnetic spectrum.
- Light is an electromagnetic waveLight is an electromagnetic wave.
- Uses of electromagnetic wavesThe electromagnetic spectrum is a family of waves, and each region is useful for a different job because the waves behave differently.
- Hazards of ultraviolet, X-rays and gamma raysUltraviolet waves, X-rays and gamma rays have high frequencies, so they carry a lot of energy.
- Using waves to see inside the bodyDoctors can look inside the body without cutting it open because different materials absorb, reflect and transmit waves differently.
- Radio waves and electrical circuitsRadio waves are produced by oscillations in electrical circuits.
- How substances interact with electromagnetic wavesWhen an electromagnetic wave meets a substance, it can be absorbed, transmitted, reflected or refracted.
- Wave speed and refractionAll electromagnetic waves travel at the same speed in a vacuum, about 3 × 108 m/s.
- Reflection, refraction and lenses in ray diagramsIn a ray diagram light is drawn as straight lines with arrows.
- Constructing ray diagrams for reflection and refractionTo construct a ray diagram for reflection, use a ruler and a sharp pencil.
- Colour, absorption, transmission and reflectionThe colour of an opaque object depends on which colours of light its surface reflects and which it absorbs.