Waves Flashcards
What do waves transfer?
energy and information in the direction that they are travelling in
What happens when waves travel through a medium?
-The particles of the medium vibrates
-These particles then transfer energy and information between each other
-Overall particles stay in the same place-only energy and information transferred
What is the amplitude of a wave?
The displacement from rest position to a crest or trough
What is the wavelength?
-The length of a full cycle of the wave (e.g crest to crest or compression to compression)
What is the frequency of a wave?
-The number of full cycles of the wave passing a certain point per second
-Measured in hertz (Hz)
-1 Hz = 1 wave per second
What is the period of a wave?
-The number of seconds it takes for a full cycle of the wave to pass a point
-Period = 1 / frequency
Transverse waves
-Vibrations are perpendicular to direction wave is travelling
-Waves that are transverse include:
All EM waves
S-waves
Ripples and waves in water
Longitudinal waves
-Vibrations are parallel to the direction the wave travels
-waves squash up and stretch out the arrangement of particles in the medium they pass through
-Make compressions (high pressure) and rarefactions (low pressure)
Wave speed (with equation)
-Tells you how quickly a wave moves through space
v (m/s or wave speed) = f (Hz or frequency) x λ (m or wavelength)
Oscilloscope practical steps - measuring the speed of sound
1) Set up the oscilloscope so detected waves at each microphone are shown as separate waves
2) Start with both microphones next to speaker, then move one away until two waves are aligned but have moved one wavelength apart
3) Measure distance between microphones to find one wavelength (λ).
4) Use wave speed equation to find speed of sounds waves through the air
Water ripples using a strobe light practical steps- Measure speed of water
1) Use signal generator attached to dipper of ripple tank to create a set frequency
2) Dim lights and turn on strobe lights to reveal wave pattern
3) Alter frequency of strobe light until wave pattern on the screen appears to ‘freeze’ or stop moving
4) Distance between each shadow line is equal to one wavelength. Measure the distance between 10 waves and find the average wavelength.
5) Use v = f x λ to calculate speed of waves
What to do if the waves seen on screen are magnified? - wave ripple practical
- Stick a piece of tape of a known length, e.g 10cm, onto bottom of ripple tank then measure its shadow
- If shadow is longer than the tape, then the length of shadow ÷ by actual length of tape will give you the scale factor.
Peak frequency practical - find speed of waves in solids
-You can find speed of waves in solid by measuring the frequency of sound waves produced when hitting object:
1) Measure and record the length of a metal rod
2) Set up apparatus making sure to secure the rod at its centre
3) Tap the rod with the hammer. Write down peak (loudest) frequency displayed by computer.
4) Repeat this three times to get a average peak frequency
5) Calculate speed of the wave using v = f x λ where λ = twice the length of the rod
Refraction in terms of an EM wave
-EM waves usually travel more slowly in denser materials
-Shorter EM wavelengths bend more. This can lead to dispersion (e.g white light becoming a spectrum)
Frequency of a wave
-The frequency of a wave stays the same when it crosses the boundary.
-As v = f x λ, change in speed caused by change in wavelength
Ray diagram construction - Steps
1) First, start by drawing the boundary between your two materials and the normal. The normal is drawn perpendicular to surface at point of incidence.
2)Draw incident ray that meets normal at boundary. Angle between ray and normal is angle of incidence (use protractor)
3) Draw refracted ray on other side of boundary
4)If second material is optically denser than first, refracted ray bends towards the normal. If less dense, refracted ray bends away from normal.
Why do the glass block experiment in a dim room?
-So you can clearly see the ray.
-Ray of light must be thin, so you can easily see the middle of the ray when tracing it and measuring angles from it.
How are sound waves caused?
- Sound waves caused by vibrating objects
- They pass through the surrounding medium in a series of compressions and rarefactions
Describe the interaction between a sound wave and a solid surfaces
- When the sound wave reaches a solid, some of the energy it is transferring is reflected and some is transmitted through the solid or absorbed by it.
- A sound wave causes changes in pressure on the surface of a solid. This causes particles in the solid to vibrate and so the disturbance is passed from the air to the solid.
- The vibrations in the solid can be passed on both as longitudanal waves and tranverse waves.
SP4e Ears and hearing
Describe the way the human ear works.
- Sound waves enter the ear canal
- The eardrum is a thin membrane, sound waves make it vibrate.
- Vibrations are passed on to tiny bones which amplify the vibrations ( make them bigger )
- Vibrations are passed on the liquid inside the cochlea
- Tiny hairs inside the cochlea detect these vibrations and create electrical signals called impulses
- Impulses travel along neurones in the auditory nerve to reach the brain.
SP4e Ears and hearing
Describe what the cochlea is and how it works.
What is it:
- The cochlea is a coiled tube containing a liquid. It can detect the different frequencies of sound reaching the ear.
How it works:
- The membrane in the middle of the tube is thicker and stiffer at the base and thinner at the apex.
- The part of the membrane that vibrates depends on the frequency of the sound wave in the liquid inside the cochlea, as different thicknesses of the membrane vibrate best at different frequencies.
- There are thousands of hair cells along the neurone that sends impulses to the brain.
How does the wavelength of a sound wave change?
- It gets longer when the wave speeds up an shorter when it slows down.
- Echoes are just reflected sound waves
What does a higher frequency mean?
A higher frequency sound wave has a higher pitch
A) What is Infrasound?
B) Describe the uses of Infrasound
A) Infrasound is sound waves with a frequency below 20Hz
B) Exploration of the earth’s core
- Scientists use information about the time the waves and the speed of the waves in different rocks to model the paths the waves have taken through earth
- P waves are longitudanal waves, meaning they can be transmitted by solids, liquid, and gases while S waves are transverse waves, so they can only be transmitted by solid objects.
- This explain the existence of shadow zones as S waves pass through the earth.
SP4f Ultrasound
A) What is Ultrasound?
B) Describe the uses of Ultrasound
A) Ultrasound is sound waves with a frequency above 20,000Hz
B1) Sonar
- Sonar equipment on ships can be used to find out how deep an area of sea is.
- A loudspeaker on the ship emits a pulse of ultrasound, this spreads out through the water and some of it is relfected by the sea bed.
B2) Ultrasound Scans
- Ultrasound can be used to produce detailed images of unborn babies so doctors can monitor how well the fetus is growing.
- A gel is used to stop the ultrasound from just reflecting from the skin.
