What are waves?
Disturbances which travel through a medium, causing particles to oscillate and transfer energy to each other. Waves transfer energy but not matter.
What is the amplitude of a wave?
The maximum displacement of a point on a wave from its undisturbed position.
What is the wavelength of a wave?
The distance between the same point on two adjacent waves (e.g. trough -> trough).
What is the frequency of a wave?
The number of complete waves passing a point per second.
What is frequency measured in?
Hertz (Hz). 1 Hz = 1 wave/second.
What is wave speed?
The speed at which energy is transferred as a result of a wave (the same as the speed the wave is moving at).
What equation can be used to find wave speed?
What is the period of a wave?
The amount of time it takes for one full wave to pass a point.
The formula for period is given in the exam. What is the period of a wave with speed 8 m/s and wavelength 2m?
Use v = fλ to work out the wave's frequency: 8 = f x 2 so f = 4 Hz
Period = 1/frequency = 1/4 = 0.25 s
What are transverse waves?
Waves whose oscillations are perpendicular to the direction of propogation of the wave (or the direction of energy transfer).
What are longitudinal waves?
Waves whose oscillations are parallel to the direction of propogation of the wave (or the direction of energy transfer).
Name 3 transverse waves.
EM waves, water ripples and S-waves.
Are electromagnetic waves transverse or longitudinal?
Name 2 longitudinal waves.
Sound waves and P-waves.
Are sound waves transverse or longitudinal?
What is the speed of sound in air?
Describe how you could use an oscilloscope to measure the speed of sound in air.
- Attach a signal generator to a speaker.
- Connect 2 microphones to an oscilloscope.
- Place both microphones next to the speaker, slowly moving one away until the waves on the oscilloscope's display are alligned, but have moved one wavelength apart.
- Measure the distance between the microphones to find one wavelength.
- Use v = fλ to find the wave speed - frequency is what the signal generator was set to.
- Check your result is about 330 m/s.
What three things can happen when a wave arrives at a boundary between two mediums?
- The wave is absorbed, transferring energy to the medium's energy stores.
- The wave is transmitted (carries on travelling through the new medium. Most of the time, it is refracted.
- The wave is reflected.
What happens depends on the wavelength of the wave and the properties of the mediums.
What rule applies to all types of reflection?
Angle of incidence = angle of reflection.
θi = θr
When drawing reflection/refraction, what is the normal?
An imaginary line perpendicular to the surface at the point of incidence (the point where the wave hits the boundary).
What are the two types of reflection?
Specular and diffuse.
What is specular reflection?
Where a wave is reflected by a smooth surface and in a single direction.
What is diffuse reflection?
Where a wave is reflected by a rough surface, and the reflected rays are scattered in different directions.
This happens because the normal is different for each incident ray. But θi = θr still applies.
Why do some surfaces appear matte and some shiny?
Shiny: taking a mirror for example, the surface is smooth, so specular reflection occurs, resulting in a clear reflection.
Matte: this happens when the surface is rough, so diffuse reflection occurs, resulting in a reflection which is not clear.
Draw a diagram of reflection.
θi = θr
What is optical density?
A measure of how quickly light travels through a medium. The higher the optical density, the slower light travels.
What is refraction?
When light waves are bent when they enter a new medium (which is of a different optical density to the previous medium).
If a wave, when it is refracted, slows down, it bends __ the normal. This happens when the second medium is __ than the first.
- Optically denser.
If a wave, when it is refracted, speeds up, it bends __ the normal. This happens when the second medium is __ than the first.
What happens to the wavelength and frequency of a wave when it is refracted?
The wavelength changes, but the frequency remains the same.