Topic 4 Waves Flashcards
Recall that waves
transfer energy and information without
transferring matter
Describe evidence that with water and sound waves it is the
wave and not the water or air itself that travels
the particles of water or air vibrate and transfer energy, but they don’t move with the wave
Define and use the terms frequency and wavelength as applied
to waves
Frequency: Number of waves passing a fixed point per second
Wavelength: The distance from a point on one wave to the same point on the adjacent wave
Define amplitude
amplitude= distance from the middle to the top or bottom, in m. The greater the amplitude the louder the sound
Define period
length of time it takes one wave to pass a given point
Wave velocity
speed of the wave in the direction it is traveling, waves travel at different speeds in different materials
Wavefront
an imaginary surface used to visualize a wave, representing points that are at the same phase in their cycle. Imagine a line connecting all the peaks or troughs of a series of waves; that line is a wavefront.
Longitudinal wave
Waves where oscillations are parallel to direction of energy transfer
Transverse Wave
Waves where oscillations are perpendicular to direction of energy transfer
Give 3 examples of longitudinal and transverse waves
Longitudinal
sound waves
Ultrasound waves
Seismic P waves
Transverse:
Water waves (ripples)
EM waves
Seismic S waves
Recall and use both the equations below for all waves:
wave speed (metre/second, m/s) =
wave speed (metre/second, m/s) =
frequency (hertz, Hz) × wavelength (metre, m)
v = f × λ
distance (metre, m) ÷ time (second, s)
v = x (or d)/t
How do we set up an experiment to find out velocity of ripples on water
Measure the length of a tub/container and record it
Fill it up with water (around 5cm high)
Lift it up (record the height) and drop the tub
Record how many times the ripples to one end of the tub and back in a given time (say 30s)
Repeat this 3 times to get the mean and do the distance travelled/time to get the wave speed
How do we set up an experiment to find out the speed of sound
Stay a set distance (recorded) away from someone else, who has a megaphone (preferably over 330m)
The person with a megaphone sends a hand signal when he shouts in there
When you see the hand signal, you start the stopwatch but when you hear the sound you end the stopwatch and record the time
You do distance/time and find out the speed of sound
Calculate depth or distance from time and wave velocity
Same formula
distance (or depth) = speed (or wave velocity)/time
Describe the effects of reflection
Waves - including sound and light waves - can be reflected at the boundary between two different materials. The reflection of sound causes echoes.
The law of reflection states that: angle of incidence = angle of reflection. For example, if a light ray hits a surface at 32°, it will be reflected at 32°. The angles of incidence and reflection are measured between the light ray and the normal- an imaginary line at 90° to the surface.
Describe the effects of refraction
If a ray goes from a low to high density medium the ray refracts towards the normal and its the opposite for the other way round
For a given frequency of light, the wavelength is proportional to the wave speed: wave speed = frequency × wavelength
So if a wave slows down (going into a more dense medium), its wavelength will decrease.
Where are the incident ray and refracted ray located
the angle from the top of the normal to the incident ray is the angle of incidence
The angle from the bottom of the normal to the refracted ray is the angle of refraction
Describe the effects of transmission and absorption of waves on surfaces
Transmitted: A wave is passed across or through a material (medium), eg light waves are transmitted through air, glass and water.
Absorbed: Energy is ‘taken-in’ by the material and the internal energy of the material will increase, eg infrared radiation from the Sun is absorbed by the surface of the Earth.
Recall that sound with frequencies greater than
20 000 hertz, Hz, is known as
ultrasound
Recall that sound with frequencies less than 20 hertz,
Hz, is known as
infrasound
Uses of infrasound
Investigating the earths surface:
Seismic waves:
S waves only travel through solids and aren’t detected on the other side of the earth (from when the earthquake happened)
P waves travel through both solids and liquids and are detected on the other side, suggesting that the earth has a solid mantle and a liquid inner core
Uses of Ultrasound: Foetal scanning
Foetal scanning:
Ultrasound wave is sent to a patient’s body. It passes through the body and reflect off the organs and tissues
The device then uses the reflected ultrasound waves to produce and image of the foetus
Ultrasound is safe and therefore doesn’t damage cells
Uses of ultrasound: Sonars
Sonars:
When ultrasound waves are emitted they reflect off boundaries and their echoes are detected
The speed of the ultrasound is known and also the time it takes to detect the echoes
distance = s/t is used to find distance travelled
distance travelled is halved to give distance between the emitter and boundary
Core Practical: Investigate the suitability of equipment to
measure the speed, frequency and wavelength of a wave in a
solid and a fluid
Waves in a liquid:
Tested in another flashcard
Waves in a solid:
Measure the length of each rod using the ruler.
○ The wavelength of the wave at peak frequency will be twice this length
○ Ensure this is measured in metres
Suspend the rod from the clamp stands using the elastic bands (2 clamp stands with 2 clamps, each holding an elastic band with a rod inside)
Strike the rod at one end and use the frequency recorder (ie: on an app) to measure the peak frequency.
Record this value.
Repeat this, striking the rod up to five times and taking an average of the frequency values
Repeat the process with different types of metal rods.
Using the formula v = f , calculate the velocity of the waves in each rod using the mean λ peak frequency and the wavelength (2 x the length of the rod).
Compare these values with researched values for each type of metal – if they are close, the equipment is suitable.
