What is a transverse wave?
waves that oscillate perpendicular to the direction of energy transfer
e.g. light waves, EM waves, ripples on water
What is a longitudinal wave?
waves that oscillate parallel to the direction of energy transfer
e.g. sound wave, ultrasound
What is the amplitude?
the maximum displacement of a point on the wave from its undisturbed position
What is the wavelength?
the distance from a point on one wave to the same point on the adjacent wave
What is the frequency?
the number of waves passing a point each second
How do you calculate the time period of a wave?
T= 1/f
T= period (s)
f= frequency (Hz)
What is the definition of wave speed?
the speed at which energy is being transferred through the medium
What is the equation for wave speed?
v = f λ
wave speed= frequency x wavelength
v= m/s
λ= m
f= Hz
What are the two different types of waves?
Mechanical- waves which require a medium to travel through
- can be transverse or longitudinal
Electromagnetic- waves that do not require a medium to travel through
- always transverse
How can you measure the speed of sound waves in air?
Using an oscilloscope- by attaching a signal generator to a speaker you can generate sounds with a specific frequency and use two microphones and oscilloscope to find the wavelength
- Set up the oscilloscope so that the detected waves at each microphone are shown as separate waves
- start with both microphones next to the speaker and then slowly move one away until the two waves are aligned on the oscilloscope display but have moved 1 wavelength apart
- measure the distance between the microphones to find one wavelength
- use the formula wave speed = frequency x wavelength to find the speed of sound waves passing through the air
- the frequency is whatever you set the signal generator to
How can you measure the speed of ripples on a water surface?
Using a ripple tank (a shallow tray with a clear bottom)
- use a power pack and set the voltage, this makes the dipper vibrate and produces the frequency
- to find the wavelength, take a photograph of the wave with the ruler in the shot
- to find the frequency record a video for 10 secs and play it back in slow-mo
- Then pick a point and count the number of waves that pass that point in the given time and divide it by 10
- to calculate wave speed= frequency x wavelength
What can happen to wave once it meets the boundary between two different materials?
It can be refracted or reflected or absorbed
What is reflection?
When a wave bounces off a medium after meeting a boundary between two media
What are the two different types of reflection?
Specular: when a wave is reflected in a single direction by a smooth surface e.g. a mirror
Diffuse: when a wave is reflected by a rough surface and the reflected rays are scattered and in lots of different directions
What is refraction?
When a wave changes direction as it crosses the boundary between two media at an angle to the normal
What effect does the optical density of a material have on the speed of light through it?
The higher the optical density, the slower light waves travel through it
What is the critical angle?
The angle at which the angle of incidence causes the refracted ray to be at 90 degrees to the normal
- only happens from more optically dense to less optically dense
What is the total internal reflection?
When the angle of incidence is greater than the critical angle
What do sound waves travel through the air as?
Sound travels through the air as a series of compressions and rarefactions
What are compressions?
Regions of high pressure, the particles are close together
What are rarefactions?
regions of low pressure, the particles are spread further apart
How do we hear sounds?
- As the speaker vibrates, it meets air particles and the air particles experience a pressure change and begin to vibrate
- the series of vibrations pass the sound wave to the ear
- sound waves of a certain frequency reach your eardrum and cause it to vibrate
What is the human hearing range?
20 Hz to 20 kHz (20000Hz)
(this is limited to the size and shape of our eardrums and the structure within the ear)
What happens to sound wave as it enters a denser medium?
its velocity (wave speed) increases whilst its frequency remains constant and the wavelength increases
