TOPIC 6 - WAVES Flashcards
What way do waves transfer energy?
The direction they are travelling
What happens when waves travel through a medium?
The particles of the medium oscillate and transfer energy between each other. But overall, the particles stay in the same place - only energy is transferred.
What is the amplitude?
The maximum displacement of a point on the wave from its undisturbed position.
What is the wavelength?
The distance between the same point on two adjacent waves. E.g. through the trough of one wave and the trough of the wave next to it.
What is the frequency?
The number of complete waves passing a certain point per second. Frequency is measured in hertz (Hz). 1 Hz is one wave per second.
What equation links period and frequency?
period = 1/frequency
What are transverse waves?
The oscillations are perpendicular to the direction of energy transfer.
Give examples of transverse waves
all electromagnetic waves
ripples and waves in water
a wave on a string
What are longitudinal waves?
The oscillations are parallel to the direction of energy transfer.
Give examples of longitudinal waves
Sound waves eg ultrasound
Shock waves eg some seismic waves
What is the equation for wave speed?
Wave speed = frequency x wavelength.
What is used to measure the speed of sound?
Oscilloscope.
Set up an oscilloscope so the detected waves at each microphone are shown as separate waves.
Start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display, but have moved exactly one wavelength apart.
Measure the distance between the microphones to find one wavelength.
How can you measure the speed of water ripples?
Using a lamp
Using a signal generator attached to the dipper of a ripple tank you can create water waves at a set frequency.
Use a lamp to see wave crests on a screen below the tank.
The distance between each shadow line is equal to one wavelength.
Measure the distance between the shadow lines that are 10 wavelengths apart, then divide the distance by 10 to find the average wavelength.
If it is difficult to measure the distance, then a photo can be taken.
What do you use for waves on strings?
Vibration transducer.
What happens when a wave arrives at a boundary?
The waves are absorbed by the material - this transfers energy to the material’s energy stores.
The waves are transmitted - the waves carry on travelling through the new material, this often leads to refraction.
The waves are reflected.
What happens when a wave is reflected?
the angle of incidence = angle of reflection
What is the angle of incidence?
The angle between the incoming wave and the normal.
What is the angle of reflection?
The angle between the reflected wave and the normal.
What is the normal?
An imaginary line that is perpendicular to the surface at the point of incidence. (the point where the wave hits the boundary).
The normal is usually drawn as a dotted line.
What is specular reflection?
Happens when a wave is reflected in a single direction by a smooth surface. E.g. when light is reflected by a mirror you get a nice, clear reflection.
What is diffuse reflection?
When a wave is reflected by a rough surface eg a piece of paper, and the reflected waves are scattered in lots of different directions.
This happens because the normal is different for each incoming ray, which means the angle of incidence is different for each ray. The rule of angle of incidence = angle of reflection still applies.
What happens when light is reflected by a rough surface?
The surface appears matte and you don’t get a clear reflection of objects.
What type of waves are electromagnetic waves?
Transverse. They transfer energy from a source to an absorber.
All EM waves travel at the same speed through air or a vacuum (space).
EM waves form a continuous spectrum over a range of frequencies.
List the EM spectrum, in order of increasing frequency/decreasing wavelenth.
Radio waves Micro waves Infra red Visible light Ultra violet X-rays Gamma rays