3. Waves Flashcards
Waves
Oscillations in a medium that transfer energy not matter. Examples are water waves, electromagnetic waves and sound waves.
Can be shown as a series of wavefronts moving away from the source of vibration, transferring energy
Peaks
High points / Crests
Troughs
Low points
Medium
The material through which a wave passes. The plural of medium is ‘media’. Waves travel at different speeds in different media.
Electromagnetic waves
Transerve waves that are vibrations in electric and magnetic fields. These are the waves that transfer energy across the Universe. Electromagnetic waves of different wavelengths make up the electromagnetic spectrum.
Wavefront
A line showing where all the points of the wave are being disturbed in the same way – for example, where all of the crests (peaks) of the waves are at a particular time.
Wavefronts are parallel to the propagation of the wave (direction the waves are travelling)
Direction of propagation
The direction that a wave travels in, this is the direction that energy is transferred.
Transverse wave
The particle oscillates perpendicular (at right angles) to the direction of propagation of the wave
(traditional wave form)
(Particle stays the same length from the source of the wave. It only oscillates (moves) up an down, forming a wave)
Longitudinal waves
The oscillation of the particles is parallel (in the same direction) to the direction of propagation of the wave.
(Particles move back and forth but always end up back where they began. eg. to the right, then to the left etc.)
Wave made of compressions and rarefactions.
Compression - Particles are closer together than normal due to a sound wave passing through it.
Rarefaction - Particles are further apart than normal due to a sound wave passing through it.
(Drawn as a transverse wave where compression = peak and rarefaction = trough)
Examples of transverse waves
- Ripples along water surface –> water moves up and down but wave motion is outwards, along water surface.
- Waves formind in a shaken rope –> wave moves along the length of the rope while the vibrations are from side to side (or up and down)
- Visible light + other electromagnetic radiation –> However, no vibrating particles. Instead there are vibrating electric and magnetic fields –> Vibration in these fields = perpendicular to the derection the radiation travels.
Wave speed (info)
- Measured in m/s
- Moves at the same speed throughout a medium (doesn’t differ between peaks and troughs)
Frequency of a wave
- Number of complete waves (1 wavelength –> from peak to peak/trough to trough) that pass a point each second
- Frequency measured with a unit called hertz (Hz)
- 1 Hz = one complete vibration per second
- 1 kHz (kilohertz) = 1000 Hz
Hertz
The unit of measurement for frequency. Symbol Hz. 1 Hz equals one complete wave/oscillation passes per second.
Wavelength
- The distance between one wave crest (peak) and the next.
- Or the distance between one trough and the next.
- As wavelength is a distance, it is measured in metres (m).
Amplitude
- The distance between the wave crest (peak) and the centre of the wave
- This is the greatest distance a particle moves from its rest position.
- The higher the amplitude a wave has, the more energy it transfers as it moves.
Wave speed (formula)
wave speed (m/s) = frequency (Hz) × wavelength (m)
v = f λ
λ = lamba (greek letter) –> represents wavelength in the formula.
Speed of a wave through a certain medium is fixed. All waves have the same speed through air.
Earthquake waves
Earthquakes are caused by sudden movement of the Earth’s crust. Enormous forces build up as continental plates push against each other and large amounts of energy are released as the pressure becomes too much and the plates slip past each other. These events cause two different types of a waves:
Primary wave and Secondary wave
Primary wave (earthquakes)
Primary waves are longitudinal waves. The ground is compressed in the same direction as the wave travels.
This can shake buildings from side to side as the wave passes through the ground beneath them.
Secondary waves (earthquakes)
Secondary waves are transverse waves. The ground rises and falls as the wave passes through it.
This will shake buildings up and down.
Reflection
A change in direction of a wave as it reaches a boundary.
‘Wave bounces back off the boundary’
Refraction
When a wave changes direction due to it changing speed when it moves from one material to another.
Refraction causes a change in direction unless the light enters along the normal.
Diffraction
The spreading of a wave as it moves through a gap or past the edge of an obstacle.
Reflection - Incident wave / wavefront
The wave / wavefront before it reaches the boundary
Reflection - Reflected wave / wavefront
Wave / wavefront after it has hit the boundary and bounced off.
- If the wavefront is parallel to the surface when it hits, the wavefront will be reflected back in the direction it came from.
- If the wavefront hits the surface at an angle, then its direction of travel will change.
- During reflection, the wave speed, frequency and wavelength does not change. Only the direction in which the wavefront is travelling changes.