Waves Flashcards
(48 cards)
Define displacement as applied to wave motion
The displacement of any particle of the wave is its distance in a given direction from the rest or
equilibrium position. It is a vector quantity.
State the meaning of the term amplitude
The amplitude is the magnitude of the maximum displacement of any particle on the wave from its
equilibrium or rest position. It is a scalar quantity.
Define Frequency, f
The frequency of a wave is the number of cycles of a wave that pass a given point in one second.
State the meaning of the term phase difference
Phase difference is the difference in position of 2 points within a cycle of oscillation. It is given as a
fraction of the cycle or as an angle (where one whole cycle is 2π or 360°) together with a statement
of which point is ahead in the cycle.
Define Wavelength, λ
The wavelength of a progressive wave is the minimum distance, measured along the direction of
propagation, between two points on the wave oscillating in phase.
Explain what is meant by wave speed, v
The speed of a wave is the distance that the wave profile moves per unit time. SI unit: ms-1
Describe how a transverse wave differs from a longitudinal wave.
A transverse wave is one where the particle oscillations are at right angles to the direction of travel
of the wave energy.
A longitudinal wave is one where the particle oscillations are parallel to the direction of travel of
the wave energy.
Explain what is meant by a progressive wave.
A progressive wave is a pattern of disturbances travelling through a medium and carrying energy
with it, involving the particles of the medium oscillating about their equilibrium positions.
Explain briefly what is meant by the term progressive when used to describe wave motion.
In a progressive wave, the wave profile can be seen to propagate (move forward) and so transfer
energy in direction of travel of the wave.
Describe what is meant by a plane polarised wave
A polarised wave is a transverse wave in which particle oscillations occur in only one of the
directions at right angles to the direction of wave propagation.
State two properties which distinguish electromagnetic waves from other transverse waves.
- electromagnetic waves can travel through a vacuum.
- electromagnetic waves are oscillating electric and magnetic fields.
State one similarity and one difference between X-rays and radio waves.
- Both are transverse waves
- Both travel at the same speed in a vacuum
- Both be can be polarised.
- They have different wavelengths,
- They have different frequencies and
- They have different (photon) energies.
Explain the term Intensity
The intensity is of a wave is the radiant power per unit area perpendicular to the direction of energy
transfer.
Explain what is meant by infrared radiation
Infrared is part of the electromagnetic spectrum. It has longer wavelength (and lower frequency)
than light.
Electromagnetic waves and sound waves can be reflected. State two other wave phenomena
that apply to both electromagnetic waves and sound waves.
- Both can be refracted
- Both can be diffracted
- Both can experience constructive and destructive interference.
Explain why electromagnetic waves can be polarised but sound waves cannot be polarised.
Electromagnetic waves are transverse; sound waves are longitudinal waves. Only transverse waves
can be polarised.
State Snell’s law
At the boundary between any two given materials, the ratio of the sine of the angle of incidence to
the sine of the angle of refraction is a constant
Define refractive index
For light, Snell’s law may be written: n1 sin θ1 = n2 sin θ 2 in which θ1 and θ2 are angles to the
normal for light passing between medium 1 and medium 2; n1 and n2 are called the refractive
indices of medium 1 and medium 2 respectively.
Define critical angle
When light approaches the boundary between two media from the ‘slower’ medium, the critical
angle is the largest angle of incidence for which refraction can occur. The refracted wave is then
travelling at 90° to the normal.
Explain what is meant by total internal reflection
When light travels through one transparent material towards the boundary with a second transparent
material with a lower refractive index, all the light is reflected at the boundary if the angle of
incidence is greater than the critical angle. This is total internal reflection.
A glass fibre used for the transmission of data consists of a central glass core with a cladding
of glass of lower refractive index. Suggest one advantage of having a glass cladding rather
than simply an air surround.
- The beam is confined to small angle to axis and so there will be fewer reflections and so less
spreading of the pulses. - The cladding prevents damage (scratches) to the surface of the core which result in light being
lost into the cladding.
What is a monomode fibre?
A monomode fibre is an optical fibre whose diameter is equal to a few wavelengths of the
transmitted light. This ensures that the light only propagates along one path parallel to axis without
being reflected.
Explain the advantage of a monomode fibre over a fibre with a much thicker core, for the
transmission of a rapid stream of data.
In a monomode fibre there is only one route or path for the light to follow whereas in a multimode
fibre there are many paths. Therefore, in a monomode fibre each pulse arrives without any
spreading and so there is less chance of pulses overlapping.
Give two advantages of using optical fibres rather than copper wires for transmitting
information.
- The bandwidth is greater and so there is a larger information-carrying capacity.
- There is less attenuation of the signal in optical fibres and so data can be transmitted over
greater distances before boosting is required. - Optical fibres are more secure than copper cables and so less susceptible to unauthorised access
to transmitted data (i.e. tapping).
