Chapter 4 Flashcards
What is a wave?
- A periodic disturbance and is continuous
- Something that has travelled away from equilibrium position
How would you classify a mechanical wave?
Some physical material is being disturbed
Give some examples of mechanical waves
Sound waves within water or air, seismic waves
How would you classify an electromagnetic wave?
Disturbance in electric or magnetic fields. No matter or particles are required.
Which of mechanical and electromagnetic waves can travel through a vacuum?
Electromagnetic
Give examples of electromagnetic waves
Radio, microwave, infrared, visible, ultraviolet, x-ray, gamma rays
How would you classify a transverse wave?
A disturbance which creates the wave. Oscillations are moving perpendicular to the direction of energy transfer
How would you classify a longitudinal wave?
The disturbance creates the wave. Oscillations are moving parallel to the direction of energy transfer
What are compressions in a wave?
Where the particles in a wave are closer together
What are rarefractions in a wave?
Where the particles in a wave are further apart
With compressions are rarefractions, which has a higher pressure?
- Compressions have a higher pressure
- Rarefractions have a lower pressure
Which type of waves can be polarised?
Transverse waves
How does polarisation work?
A transverse wave passes through a polaroid, and the polaroid only allows displacement from equilibrium in one direction, and the plane is defined
What is the direction of displacement like in an unpolarised wave?
In all directions
Describe the graph of the intensity of signal against angle of rotation for: The unpolarised ray passing through 2 polaroids, and the 2nd one being rotated
0 deg - full intensity
90 deg- no intensity
180 deg - full intensity
270 deg - no intensity
On a graph, what is the difference between time period and frequency?
Time period is the duration of one cycle
Frequency is the number of cycles in one second
What is a radian?
Unit for measuring an angle
What is the unit for radians?
It has none, it is a ratio
How many pi radians are in 360 degrees?
2 pi
What are the 2 situations that you would deal with phase difference?
- Looking at the phase difference between 2 points on the same wave
- Have 2 waves, look at phase difference at the point they meet (interference)
How would you measure the phase difference between 2 points on the same wave?
Measure lamba, and the distance between 2 points.
d/lamba gives fraction of the wave.
d/l x 2 pi = phase difference in radians
d/l x 360 = phase difference in deg
In refraction, from less dense -> more dense mediums, how does speed and wavelength change?
Speed and wavelength decrease
In refraction, from more dense -> less dense mediums, how does speed and wavelength change?
Speed and wavelength increase
What are wavefronts?
Points in a wave that have the same phase. They are perpendicular to the direction of travel
What is superposition?
When waves pass through each other, and combine for an instant
What does the superposition of waves look like for 2 waves that pass through each other and are in phase?
The amplitude and trough doubles - Constructive interference
What does the superposition of waves look like for 2 waves that pass through each other and are out fo phase?
The amplitudes and troughs cancel out, giving a flat line - Destructive interference
What is the path difference of 2 waves?
Path difference is the difference between the lengths of two paths.
What must be true about the wavelengths for constructive path difference?
The difference between paths is a multiple of the wavelength
What must be true about the wavelengths for destructive path difference?
The difference between paths is not a multiple of the wavelength
Define interference
Formation of points of cancellation or reinforcement where 2 coherent waves pass through each other
When are 2 sources of anything coherent?
2 sources of wave are coherent if they emit waves with a constant phase difference
What are oscilloscopes?
Devices that can measure voltages very accurately
What can you measure with a cathode ray oscilloscope?
Time period, amplitude and time events
