WAVES [3.2 Light, Sound] except EM Flashcards
transverse waves e.g.s
define
infra-red waves, light waves, ultraviolet waves
[Ripples on the surface of water
Vibrations on a guitar string
S-waves (a type of seismic wave)
Electromagnetic waves (such as radio, light, X-rays etc)]
Waves where the points along its length vibrate at 90 degrees to the direction of energy transfer
For transverse wave:
ONLY EM WAVES TRAVEL IN VACUUM
constant density
pressure constant
speed of wave is depending on material it is travelling in
energy transfer is perpendicular to wave motion
They transfer energy, but not the particles of the medium
They can move in solids and on the surfaces of liquids but NOT inside liquids or gases
Some transverse waves (electromagnetic waves) can move in solids, liquids and gases and in a vacuum
LONGITUDINAL waves!
Waves where the points along its length vibrate parallel to the direction of energy transfer
For a longitudinal wave:
CANNOT travel in a VACUUM
changes in density
changes in pressure
speed of wave is depending on material it is travelling in
The energy transfer is in the same direction as the wave motion
They transfer energy, but not the particles of the medium
They can move in solids, liquids and gases
They can not move in a vacuum (since there are no particles)
📌 The key features of a longitudinal wave are where the points are:
Close together, called compressions
Spaced apart, called rarefactions
Examples of longitudinal waves are:
Sound waves
P-waves (a type of seismic wave)
Pressure waves caused by repeated movements in a liquid or gas
Longitudinal waves are usually drawn as several lines to show that the wave is moving parallel to the direction of energy transfer
Drawing the lines closer together represents the compressions
Drawing the lines further apart represents the rarefactions
Wave behaviour - Reflection, Refraction & Diffraction
Reflection occurs when:
A wave hits a boundary between two media and does not pass through, but instead stays in the original medium
law of reflection states
The angle of incidence = The angle of reflection
FIRST SIDE OF RAY COMING IN
angle of incidence
Refraction
occurs when:
When waves enter a different medium, their speed can change
A wave passes a boundary between two different transparent media and undergoes a change in speed
When a wave refracts, as well as a change in speed, the wave also undergoes:
A change in wavelength (but frequency stays the same)
A change in direction
;; Waves can change direction when moving between materials with different densities
If the waves slow down
the waves will bunch together, causing the wavelength to decrease
The waves will also start to turn slightly towards the normal
If the waves speed up
waves will spread out, causing the wavelength to increase
The waves will also turn slightly away from the normal
Diffraction
DIFFRACTION, REFRACTION, REFLECTION - all “wave effects”
When waves pass through a narrow gap, the waves spread out
When drawing waves being reflected take care to:
Make sure that the angle of incidence is equal to the angle of reflection
Keep the wavelength of the waves the same
Similarly, when waves are diffracted the wavelength remains constant.
Refraction is the only wave effect in which the wavelength changes.
Remember:
Refraction is the name given to the change in the speed of a wave when it passes from one medium to another. The change in direction is a consequence of this.
Factors Affecting Diffraction
-> extent of diffraction depends on the width of the gap compared with the wavelength of the waves
Diffraction is the most prominent when the ______________
MOST prominent when width of the slit is approximately equal to the wavelength
As the gap gets bigger
the effect gradually gets less pronounced until, in the case that the gap is very much larger than the wavelength, the waves no longer spread out at all
Diffraction can also occur when waves pass an edge
When a wave goes past the edge of a barrier, the waves can curve around the edge
Investigating Waves with a Ripple Tank
Ripple tanks are commonly used in experiments to demonstrate the following properties of water waves:
Reflection at a plane surface
Refraction due to a change in speed caused by a change in depth
Diffraction due to a gap
Diffraction due to an edge
Investigating Reflection
Reflection can be shown by the waves hitting a plane (straight) surface, such as a wall or mirror
Investigating Refraction
SHALLOW water = DECREASE in wavelength, SLOWER
When water waves travel from deep areas to shallow areas they slow down
Refraction can be shown by placing a glass block in the tank
The glass block should sit below the surface of the water and cover only some of the tank floor
The depth of water becomes shallower here the glass block is placed
Since speed depends on depth, the ripples slow down when travelling over the block
This is a good model of refraction showing how waves slow down when passing from deep water into shallow water
Investigating Diffraction
Diffraction can be shown in a ripple tank by placing small barriers and obstacles in the tank
As the water waves encounter two obstacles with a gap between them, the waves can be seen to spread out as follows:
amount of diffraction depends
depends on the size of the gap compared to the wavelength of the water wave
DIFFRACTION;; how the wavelengths differ with frequency in a ripple tank
The higher the frequency of the motor, the shorter the wavelength
The lower the frequency of the motor, the longer the wavelength