Waves Flashcards
What is a wave
transfers energy from one place to another without any overall transfer of matter. To make a wave, a medium needs to vibrate
Mediums
Particles or an electromagnetic field
Transverse waves
In a transverse wave vibrations are at right angles (perpendicular) to the direction of energy transfer
(direction of the wave). These vibrations cause peaks and troughs.
Waves on the surface of water (ripples) and all electromagnetic radiation such as visible light are
examples of transverse waves.
Longitudinal waves
In a longitudinal wave vibrations are in the same direction (parallel) as the direction of energy
transfer (direction of the wave). These vibrations cause compressions and rarefactions.
Sound is an example of a longitudinal wave.
Particles in longitudinal wave are far apart
Rarefaction
Time period
Time for one vibration or time for wave to pass a point
Amplitude
maximum displacement of a vibration from its rest position
Calculating speed of sound experiment
Person one should stand a large distance away from person two and make an obvious visible sound. The distance between them (at least 100m) should be measured with a tape measure. Person two should start their stop clock when they see the sound being made and stop it when they hear the sound. The speed of sound can then be calculated from speed = distance / time.
Wave speed experiment from ripple tank
measure the distance across ten waves using a ruler and then divide by 10 to find one wavelength. You can read the frequency from the signal generator that is driving the ripple tank making the waves. The speed can then be calculated using speed = frequency x wavelength.
Speed of wave on string experiment
Stretch a string over a pulley using masses. Use a frequency generator to generate a wave in the string.
Measure the wavelength when a clear wave is shown and note the frequency on the generator. Use the wave speed equation to determine the speed.
Specular reflection
light is incident on smooth surfaces. Parallel rays of incident light are reflected in a predictable manner and remain parallel to each other upon reflection.
Diffuse reflection
happens on rough surfaces. Parallel rays of light do not remain parallel to each other on reflection and are scattered in different directions.
Virtual vs Real image
A virtual image is one from which the light rays appear to come but don’t actually come from the image e.g. the image seen in a mirror. A real image is one where the light rays do come from.
Refraction
change in speed of a wave when it reaches the boundary between two different materials. It happens because materials have different optical densities. It causes the wave to change direction.
Refraction affect on wavelength
If a wave refracts because it speeds up then its wavelength will increase.
If a wave refracts because it slows down then its wavelength will decrease.
Refraction of light at water/air boundaries
Makes things in cups/ glassess appear closer to water surface
Convex vs concave lenses
Rays converge in convex and disperse in concave
LIght in a prism
separate colours of the spectrum are seen. This is called dispersion
and happens because different colour (wavelength) light changes speed by different amounts.
Transparent/ transluscent objects
Transparent and translucent objects both transmit light that is incident on them, but translucent objects do so only partially.
Filters
filters only allow light of the wavselength corresponding to its colour to pass through it (be transmitted). All other wavelengths are absorbed.
What happens to an object viewed through a filter
If the filter allows the wavelength of light corresponding to the object to pass it will look the colour it is. If the filter does not allow the wavelength of light corresponding to the object to pass it will look black.
