What is meant by the amplitude of a wave?
The maximum displacement of a vibrating particle
What is meant by the wavelength of a wave?
The least distance between two adjacent vibrating particles with the same displacement and velocity at the same time
What is meant by the period of a wave?
The time for one complete wave to pass to a fixed point
What is meant by the frequency of a wave?
The number of complete waves passing a point per second
What is the equation for the period of a wave
Period = 1/f
What is meant by refraction
Change of direction of a wave when it crosses a boundary where it spied changes
What is meant by diffraction?
Spreading of waves on passing through a gap
State the principle of superposition
When two waves meet, the total displacement at a point is equal to the sum of the individual displacements at that point
What is meant by the displacement of a vibrating particle
The distance and direction from the equilibrium position
How is a stationary wave formed?
- Two progressive waves in the same medium
- Travel in opposite directions
- With the same wavelength, speed, frequency and amplitude
- They combine at fixed points to form nodes
What is meant by interference?
Formation of points of cancellation and reinforcement where two coherent waves pass through each other
What is meant when two sources of waves are coherent
They emit waves with a constant phase difference
What machine can be used to demonstrate reflection, refraction, diffraction, interference and polarisation if microwaves?
A microwave transmitter and receiver
State and explain advantages associated with a smaller diameter optical fibre core.
- less multipath dispersion
- less light is lost
- better quality signal / less distortion
- increased probability of TIR
- Less change of angle between each reflection
- improved data transfer
The red laser light is replaced by a non-laser source emitting white light.
Describe how the appearance of the pattern would change.
- central white (fringe)
- each subsidiary maxima are composed of a spectrum
- AND subsidiary maxima have violet nearest central maximum (OR red furthest from center)
- Fringe spacing less (maxima are wider)
Explain the change that occurs when you replace the light to one of a longer wavelength in a double slit
Fringe width,w, increases. Wavelength is proportional to fringe width
Explain the change that occurs when you replace the light to one of a longer wavelength in a double slit
Fringe width,w, increases. Wavelength is proportional to fringe width
Describe how he should change the way the apparatus is arranged and used in order to obtain an accurate value for the wavelength.
Increase D
when D is increased then w increases
Measure across more than 2 maxima. repeat the reading with a changed distance D
explain how the pattern of bright and dark patches is formed
slits act as coherent sources (1)
waves diffract at slits (1)
waves superpose (1)
bright patches : constructive interference as they reinforce each other (1)
dark patches : destructive interference as they cancel out (1)
Describe the interference pattern produced by monochromatic light in double slits
- alternating bright and dark fringes
- which are equally spaced
- and have very similar intensity
Describe the interference pattern produced by monochromatic light in single slits exper
- alternating bright and dark fringes
- bright central maxima
- decreasing intensity of maxima further away from the central
Describe modal dispersion and how it can be prevented (6)
- Occurs in a wide core
- Because light travelling along the horizontal axis travels a shorter distance per metre
- Than light that repeatedly undergoes TIR
- So a pulse of light sent along a wide core would become longer
- If it was too long it would merge with the next pulse
- Therefore use a narrow core
When does pulse dispersion occur?
When white light is used instead of monochromatic light
Describe material dispersion and how it can be prevented (4)
- The speed of light in the glass of the optical fibre depends on the wavelength travelling though it
- The differences in speed of each wavelength in white light
- Causes violet light to reach the end of the fibre more slowly than red light
- Monochromatic light must be used to prevent it
