Waves Flashcards
What is a wave?
A mechanism that allows energy to be moved from one place to another.
What is a transverse wave?
A wave which oscillates perpendicular to the direction of propagation and energy transfer.
What is a longitudinal wave?
A wave which oscillates parallel to the direction of propagation and energy transfer.
Give an example of a longitudinal wave.
Sound
What is the main difference between transverse and longitudinal waves?
Transverse waves can be polarised.
What is wavelength?
The distance between adjacent troughs.
What is frequency?
The number of waves passing a fixed point every second.
What is amplitude?
The distance between the centre line of the wave and the top of the crest.
What is the intensity of a wave?
- The energy deposited per second per metre squared.
- Power deposited per metre squared.
What is the intensity of a wave proportional to?
Amplitude squared
What is phase difference?
The fraction of one cycle between two vibrating points.
How can phase difference be expressed?
Wavelength or angle
What is the plane of polarisation?
The plane of oscillation of the particles that make up the wave.
What is the plane of polarisation for an EM wave?
The plane in which the electric field component vibrates.
What type of waves are slant polarised?
VHF (FM) radio waves
What is needed to form and stationary wave?
Two waves of the same type travelling towards each other that have the same frequency and amplitude.
What is an antinode?
The maximum displacement of the envelope.
What is a node?
Where the displacement of the envelope is zero.
What is a wavefront?
The line drawn along the crests of waves.
What is a ray?
A line drawn perpendicular to the wavefronts showing the direction of the wavefronts.
What two rules are always observed when reflecting at a plane mirror?
- angle of incidence = angle of reflection
- The incident and reflected ray are in the same plane.
What is the main use for mirrors reflecting light at 45°?
A periscope
What are the three properties of an image formed in a plane mirror?
- The image is virtual.
- The image is the same distance behind the mirror as the object is in front.
- The image is laterally inverted.
What is refraction?
The bending of a ray as it passes from one material into another and changes speed.
What is refraction?
The bending of a ray as it passes from one material into another and changes speed.
What is Snell’s Law?
sini/sinr = 1n2 = velocity in material 1 / velocity in material 2 = n2/n1
What does 1n2 represent?
The relative refractive index from material 1 into material 2.
What does 1n2 also equal?
- 1 / 2n1
- velocity in material 1 / velocity in material 2
What is absolute refractive index?
The relative refractive index between a vacuum and the material.
What is the critical angle?
The angle of incidence for which the angle of refraction is 90°.
What happens if the critical angle is exceeded?
Total internal reflection occurs.
What is Snell’s Law at the critical angle?
sinic = n2/n1 = velocity in material 1 / velocity in material 2
What is Snell’s Law at the critical angle?
sinic = n2/n1 = velocity in material 1 / velocity in material 2
What are the two main problems with basic fibre optics?
- If another material comes into contact with the fibre the boundary is no longer glass-air so the critical angle is changed meaning light can escape.
- If two glass fibres touch there is no boundary meaning light can travel between the two fibres.
How is multipath dispersion prevented?
Cladding made of a second layer of glass with a lower refractive index is used.
What are the two types of fibre optic bundles used for an endoscope?
- Coherent bundle
- Incoherent bundle
What type of bundle is used in an endoscope to carry light into the patient?
Incoherent bundle
What type of bundle is used in an endoscope to carry light out of the patient?
Coherent bundle
What is the resultant wave displacement of two waves arriving at a point?
The vector sum of the individual wave displacements.
When are waves coherent?
If they have the same frequency or wavelength and a constant phase relationship.
What is diffraction?
The bending of a wavefront as it passes through a gap or close to the edge of an object.
What are the two types of wave interference?
Constructive and destructive
How is the maximum constructive interference of a laser light calculated?
λ = ws / D
w = separation in maxima s = slit separation D = distance from slits to screen
How is the width of the central maxima calculated from a single slit?
w = 2λD / b
b = slit width w = central fringe width
How is the n order maxima of a diffraction grating calculated?
dsinθn = nλ
When are two polarising filters “crossed”?
When the transmitted energy is at a mimimum.
What is the period of a wave?
The time for one complete wave to pass a fixed point.
How is phase difference calculated in radians?
2πd/λ
What is superposition?
When two waves the total displacement is equal to the sum of the individual displacements.
How is a microwave used to demonstrate wave properties?
- Moving a receiver away shows that they become weaker.
- Using a metal plate shows they can be reflected.
- Using a slit shows how a larger gap reduces diffraction.
- Using a double slit can show interference.
How is the distance between two adjacent nodes calculated?
0.5λ
When does a light ray bend towards the normal?
When going into the more refractive substance
How is the refractive index of a substance calculated?
sini/sinr
What is n1sini equal to?
n2sinr
From double slit interference, what does a bright fringe show?
The light waves from each slit are in phase.
From double slit interference, what does a dark fringe show?
The two light waves are 180 out of phase
How wide is the central fringe of single slit diffraction compared to the outer fringes?
It is twice as wide
