Waves Part 1 Flashcards
what is a wave
- transfers energy from one place to another with no overall transfer of matter
- to make a wave something needs to vibrate and this can be a collection of particles or an electromagnetic field - the thing that vibrates is called a medium
what evidence is there that waves travel and matter does not
- particles do not move in sound waves or all the particles would accumulate at the end with an absence of particles in its path
- in the sea, water particles do not move with the wave otherwise there would be an absence of particles in the sea
particles vibrate around a fixed position
what is a transverse wave
- vibrations are perpendicular to the direction of energy transfer
- they have peaks and troughs
- water waves
- electromagnetic waves (light)
what is a longitudinal wave
- vibrations are parallel to the direction of energy transfer
- compressions and rarefactions
- sound waves
definition of frequency
the number of vibrations per second - measured in Hz (Hertz)
definition of time period
the time for one vibration - measured in seconds
definition of amplitude
maximum displacement of a vibration from its rest position
definition of wavelength
distance from a point on a wave to the same point on the next wave - measured in metres
relationship between time period and frequency
time period is 1/frequency
what is wave speed
speed at which energy is transferred throughout a medium
how do you measured speed of sound in air
- 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.
how can you measure speed of ripples on water surface
- Using a ripple tank you can 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.
how do you determine speed of waves on a string
- 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.
To vary speed, frequency of generator can be varied or increase tension on string by increasing the masses on the end.
difference between diffuse and specular reflection
- specular is when light is incident on smooth surfaces - reflected in a predictable manner and always reflect parallel to each other
- diffuse is when light is incident on rough surfaces - parallel rays do not remain parallel and are scattered in different directions
law of reflection
angle of incidence is equal to the angles of reflection
what is a virtual image
virtual image is one where the light appears to come from but does not actually come from - like in a mirror - whereas a real image is where the light rays are really coming from
what is refraction
- change in speed in a wave when it reaches the boundary between two different materials
- it happens as materials have different optical densities
- they cause the wave to change direction
what happens to frequency during refraction
nothing - the source of the wave does not change so nor does the frequency
what happens to wavelength during refraction
- if wave speeds up, wavelength will increase
- if wave slows down, wavelength will decrease
what effects does refraction of light have
refraction at water/air boundaries cause objects to appear closer to the water surface then they actually are - this is why straw looks broken in a glass of water
what happens to parallel rays of light when they enter a convex lens
parallel rays converge at the focal point, creating the focal length, the distance from the centre of the lens to the focus
convex diagrams
To accurately draw lens diagrams:
1. Ray from top of object horizontal to lens then down through F on other side.
2. Ray from top of object directly through the centre of the lens.
At this point the rays should cross and this is where the “top” of the image is.
A third ray can be drawn down through F nearest the object (if possible) then horizontal through the lens
to confirm the position of the image.
what happens to parallel waves of light when they enter a concave lens
parallel rays are made to diverge away from the lens - focal point is on the same side of the lens as the object
concave diagrams
To accurately draw lens diagrams:
3. Ray from top of object horizontal to lens then back through F on the same side (this bit dotted).
4. Ray from top of object directly through the centre of the lens.
At this point the rays should cross and this is where the “top” of the image is.
