
What are mechanical waves?
Waves that pass through a substance, causing particles in the substance to vibrate in such a way that causes nearby particles to also begin to vibrate

What are electromagnetic waves?
Oscillating electric and magnetic fields that progress through space without the need for a substance

What is a longitudinal wave?
Waves in which the direction of vibrational the particles is parallel to the direction in which the waves travel

What types of waves are longitudinal waves?
 Sound waves
 Primary seismic waves
 Compression waves

What is a transverse wave?
Waves in which the direction of vibration is perpendicular to the direction in which the wave travels

What types of waves are transverse waves?
 Electromagnetic waves
 Secondary seismic waves
 Waves on a string or wire

When are transverse waves planepolarised?
The vibrations stay in one plane only

What happens to unpolarised light when it passes through a Polaroid filter?
The transmitted light is polarised as the filter only allows through light which vibrates in a certain direction, according to the alignment of its molecules

When are Polaroid filters said to be 'crossed'?
When the transmitted intensity is a minimum

How do Polaroid sunglasses work?
Reflected light is polarised and the intensity is reduced

What is displacement?
A particles distance and direction from its equilibrium position

What is the amplitude of a wave?
The maximum displacement of a vibrating particle

What is the definition of wavelength?
The least difference between two adjacent vibrating particles with the same displacement and velocity at the same time

What is the period of a wave?
The time for one complete wave to pass a fixed point

What is the definition of frequency for a wave?
The number of cycles of vibration of a particle per second

What is the definition of phase difference?
The fraction of a cycle between vibrations of two particles

How do you calculate phase difference?
2 x pi x distance / wavelength

What is reflection?
Straight waves directed at a certain angle to a hard flat surface reflect off at the same angle

What is refraction?
If a wave approaches a boundary at an angle it will change direction as well as changing speed

What is diffraction?
When waves spread out after passing through a gap or around an object

What causes waves to spread out more in diffraction?
 Narrower gap
 Longer wavelength

What is 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 interference?
When cancellation and reinforcement occurs at fixed positions

How are stationary waves formed?
When two progressive waves pass through each other

How much energy do freely vibrating stationary waves transfer to their surroundings?
None

When is the phase difference between two vibrating particles zero?
If the two particles are between adjacent nodes or separated by an even number of nodes

When is the phase difference between two vibrating particles 180° (pi radians)?
If the two particles are separated by an odd number of nodes

What is the difference between two adjacent nodes?
1/2 lambda

What is the equation to calculate the frequency of the first harmonic of a stationary wave?
f = c / 2L

How do you calculate the time taken for a wave to travel along a string and back?
 2L / c
 Where c is the speed of the waves on the string

How do you calculate the time taken for the vibrator to pass through a whole number of cycles?
 m / f
 Where m is a whole number

How does an oscilloscope work?
An electron gun at one end of the glass tube emits electrons in a beam towards a fluorescent screen at the other end of the tube. Light is emitted from the spot on the screen where the beam hits the screen

If a light wave travels at an angle into a denser substance, what way will the light bend?
Towards the normal

How do you calculate the refractive index of a substance, n?
sin i / sin r

How do you calculate the refractive index of a substance, Ns?
 C / Cs (speed of light in substance)
 Lambda / lambda in substance

What is Snell's law?
n1sin1=n2sin2

What factors are needed for total internal reflection to take place?
 The incident substance has a larger refractive index than the other substance
 The angle of incidence exceeds the critical angle

What must optical fibres have to work successfully?
 Highly transparent  to minimise absorption of light
 Cladding  to reduce light lose which would reduce the amplitude of the pulses
 Very narrow  to prevent modal (multi path) dispersion

What is modal (multi path) dispersion?
 If an optical fibre has a wide core light travelling along the axis of the core travels a shorter distance than light that repeatedly undergoes total internal reflection
 Therefore a light pulse would become longer, possibly therefore merging with the next pulse

What is material or spectral dispersion?
 When white light is used in an optical fibre instead of monochromatic light
 The different coloured waves would be different speeds, causing the pulse to become longer

When using medical endoscopes, what does the term coherent bundles mean?
The fibre ends at each end of the bundle are in the same relative position

What does coherent mean?
Waves with a constant phase difference and the same frequency

What is happening when a bright fringe is formed in Young's double slit experiment?
The light from one slot reinforces the light from the other slit  the light waves arrive in phase with each other

What is happening when a dark fringe is formed in Young's double slit experiment?
The light from one slit cancels the light from the other slit  the light waves are 180° out of phase

How do you calculate fringe separation, w, in Young's double slit experiment?
 Lambda x D / s
 D = distance from the slit to the screen
 s = slit spacing, distance between the centres of the slits

Why is fringe separation greater for red light compared to blue light?
Red light has a longer wave length

What makes laser light different to other forms of light?
 It is monochromatic
 It is coherent

What do white light fringes look like?
 Central white fringe
 Tinted red on the outside
 Tinted blue on the inside
 Outer fringes become fainter
 Outer fringes merge, different colours reinforce and therefore overlap

What makes diffracted waves spread out more?
 The gap is made narrower
 The wavelength is made larger

Why do diffracted wavelengths have breaks on either side of the centre?
Waves diffracted by adjacent sections on the gap are out of phase and therefore cancel each other out in certain directions

With single slit diffraction, how do you make the fringes wider?
 Greater wavelength of light
 Make the slit narrower

How do you calculate the width of the central fringe in single slit diffraction?
Wavelength of the light / width of single slit x 2D

Why does a diffraction grating transmit light in only certain directions?
 Light passing through each slit is diffracted
 The diffracted light waves from adjacent slits reinforce each other in certain directions only

What factors increase the angle of diffraction between each transmitted beam?
 Light of a longer wavelength is used
 A grating with closer slits is used

How do you calculate the angle of diffraction of the nth order beam?
d sin = n lambda

How do you calculate the number of slits per meter on a diffraction grating?
 1/d
 Where d is the grating spacing

What increases the angle of diffraction in a diffraction grating experiment?
Increasing the number of slits per meter

How do you calculate the maximum number of orders in a diffraction grating experiment?
The value of d/lambda rounded down to the nearest whole number

