Waves Flashcards
Are electro-magnetic waves transverse or longitudinal?
Transverse
True or false:
Angle of incidence=angle of refraction
False
The angle of incidence=the angle of reflection
When a wave passes from a low density medium to a high density medium the Ray bends __________ the normal.
Towards
When a wave passes into a medium of a greater density, what happens to the speed of the wave?
The speed is slower
When a wave passes into a medium of a greater density, what happens to the wavelength of the wave?
It becomes shorter.
How do you calculate the refractive index?
Sin i/ sin r
Define refractive incidence.
The ratio of wave velocities in the two media. The refractive index “n” relates to the boundary between two media.
When does maximum diffraction occur?
When the gap size is similar to the wavelength of the wave
Are ANTINODES constructive or destructive?
Constructive
Are NODES constructive or destructive?
Destructive
What is the principle of superposition of waves?
When two waves of the same kind meet at a point in space, the resultant displacement at that point is the vector sum of the displacements that the two waves would separately produce at that point.
What is rectilinear propagation?
Waves travel in straight lines.
Why is a laser used during the demonstration of two slit wave interference experiments?
The light is monochromatic (light of only one colour).
What is POLARISATION?
When all oscillations on one plane of a wave are removed.
True or false:
Polarisation can only occur in both transverse and longitudinal waves.
False: polarisation can only occur in transverse waves.
What are the the two axes on a CRO and what does CRO stand for?
CRO = Cathode Ray Oscilloscope
Y axis: voltage
X axis: time
What is the INTENSITY of a wave?
The energy falling on unit cross-sectional area per second ➡️ Intensity=power/area
True or false:
Intensity is directly proportional to amplitude
False:
I is directly proportional to amplitude squared
Distinguish between longitudinal and transverse waves.
Transverse waves have oscillations perpendicular to the direction of propagation (energy transfer), whereas the oscillations of longitudinal waves are parallel to the propagation.
True or false:
Polarisation can occur in both transverse and longitudinal waves.
FALSE
polarisation can only occur in transverse waves because the oscillations are perpendicular to the direction of wave propogation so there are many different orientations, which can be polarised.
Define a stationary wave
A stationary wave is a wave produced by the superstition of a wave and its reflection.
What is meant by ‘progressive wave’?
A wave that transfers energy and momentum away from the source.
Distinguish between progressive waves and stationary waves by making reference to energy transfer.
Progressive waves, unlike stationary waves, transfer energy.
Why can most graphical representations of a sound wave in a closed pipe be misleading?
Sound waves are longitudinal rather than transervse and so are not, as depicted, smooth curves. The diagrams represent the oscillations of the particles.
Stationary waves can be produced in closed pipes
Why can standing waves also be produced in open ended pipes?
The change in air pressure at the end of the pipe means the wave can be reflected and thus standing waves can be formed by the superposition of the wave and its reflection.
Stringed instruments use standing waves.
How is the frequency altered?
Changing the frequency can help change the note.
The frequency depends on:
1) the mass per unit volume of the string
2) The tension of the string (can be adjusted when tuning the instrument)
3) the length of the string (increased or decreased by the musicians fingers)
A student stands midway between a pair of speakers, which are oscillating at 400Hz and 401Hz respectively. The sound waves produced by these speakers have equal amplitudes. Describe and explain what she hears.
The student will hear a periodic variation in the loudness of the sound (beats)
The phase difference between the two waves continually, and periodically changes due to the slight difference in frequency.
When the waves are in phase they will reinforce each of her, increasing the loudness of the sound. As the two waves move out of phase they cancel each other out and the loudness of sound decreases.
The frequency of the beating effect will be 1Hz.
Distinguish between a progressive wave and stationary wave by making reference to amplitude of vibration of neighbouring particles.
In a stationary wave the amplitude varies with position along waves ( from a maximum at ANTINODES and 0 at nodes).
In progressive waves - all particles have the same amplitude (at each point the displacement varies over a cycle).
Distinguish between a progressive wave and stationary wave by making reference to phase angle between particles.
Over one wavelength of a progressive wave, each particle has a different phase angle.
In a stationary wave, all the particles in one segment have the same phase angle, which is opposite to all the particles in the adjacent segment.
Show how the principle of superposition of light waves can be used to explain the formation of interference fringes when youngs double-slit is used. (8 marks)
Alternating bright fringes and dark fringes:
Bright - regions of maxima formed by the waves from each source (slit) arriving in phase, causing constructive interference. This occurs when the path difference of the waves from each slit is a whole number of wavelengths.
Dark - regions of minima, formed by the waves from each slit arriving in anti-phase, causing destructive interference. This occurs when the path difference is an odd number of half wavelengths.
State what is meant by threshold frequency.
The minimum frequency required to free electrons (due to photons of adequate size being emitted).
Describe what is meant by a plane polarised wave
A wave that has had all but one plane, perpendicular to the plane, removed by polarisation.
Explain the meaning of the term phase difference
Relates to the oscillation of two points on the wave. How far out of step one oscillation is from the other.
Explain how an under what conditions a stationary soundwave is formed in an open ended tube.
The wave reflected at the end of the pipe interferes with the incident wave to produce a resultant wave with nodes and ANTINODES. both ends must be anti-nodes.
State the principle of superposition of waves
When two waves overlap the resultant displacement is the vector sum of the individual displacements
Explain the term coherent
Waves with a constant phase difference
