# Physics Waves

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What is a longitudinal wave?
A wave that oscillates parallel to the direction of propagation.
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What is a traverse wave?
A wave the oscillated perpendicular to the direction of propagation.
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What are mechanical waves?
Waves that require a medium for transmission. They are generally produced by vibrations.
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What are the areas in a longitudinal wave?
Rarefactions and compressions. They create areas of different pressures in a gas.
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What is amplitude?
The maximum displacement from the mean position
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What is frequency?
The number of complete oscillations per second.
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What is the period?
The time taken for one complete oscillation.
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What is a waveform?
The variation of displacement with time of the particles within a wave.
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What is the phase?
The position within a cycle that the particle occupies relative to the onset of the cycle.
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When are waves/particles on a wave in phase?
If the path difference is a whole number of wavelengths or if the particles are at the same position in the cycle of the wave.
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When are waves/oscillations in antiphase?
When the oscillations are half a cycle out of step.
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What is the phase difference of oscillations in anti-phase?
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What is the phase difference of oscillations in phase?
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What is the law of reflection?
The above between the incident ray and a normal drawn at the point of reflection is equal to the angle between the reflected ray and the normal.
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How does the angle of incidence affect the proportion of light reflected?
As the angle increases, the proportion of light reflected increases.
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What is a wavefront?
A line, or surface, in a wave along which all the points are in phase.
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If the speed increases, how does the refracted ray move relative to the normal?
It bends away from the normal.
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What is the critical angle?
The angle at which the light beam travels along the boundary between two media.
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When does total internal reflection occur?
When the angle of incidence is larger than the critical angle.
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What is the focal point?
The point where parallel rays of light will meet, or appear to diverge from, after passing through the lens.
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What is the focal length?
The distance between the optical centre of the lens and the focal point.
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What happens when light passes through a converging lens?
Parallel rays of light appear to converge to a single point.
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What happens when light passes through a diverging lens?
Parallel rays of light do not converge to a point, but instead appear to diverge from a single point.
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What are the units for the power of a lens?
Dioptre (D) = m^-1
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Where does a real image form?
On the opposite side of the lens to the object.
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Where does a virtual image form?
On the same side of the lens to the object.
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What is the principle axis?
A line that passes normally through the optical centre of the lens.
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What is the optical centre?
The point though which rays of light will pass without deviation.
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What are plane polarised waves?
Transverse waves in which the oscillations occur in a single plane.
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Why can't sound waves be polarised?
They oscillate parallel to the direction of propagation.
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How are waves polarised?
Using a polarising filter, which prevents light passing through the filter except in one plane (the plane of polarisation).
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How are polymers analysed using stress analysis?
The polymers are put under stress and then viewed through crossed sheets of Polaroid. The interference stress patterns can be analysed to detect potential regions of weakness.
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What is ultrasound?
Sound waves with frequency greater than the upper threshold of human hearing (around 20kHz)
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How can pulse echo techniques be used in ultrasound imaging?
Pulses of ultrasound will be reflected back towards the transducer when they meet a boundary between two media. If the speed of the ultrasound and the time taken to return the transducer are known, the distance to the boundary can be calculated.
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Why is coupling gel applied to skin before an ultrasound image is produced?
The gel means that there is no air between the transducer and the skin, so the ultrasound will not reflect from the skin.
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Why do ultrasound images have a much lower resolution than X-ray images?
X-rays have a much shorter wavelength, so can provide more clear and detailed images as they pick up on boundaries that ultrasound images cannot.
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How can the ultrasound image be made clearer (pulse)?
Use shorter pulses so that reflections from nearby interfaces don't return before the end of the pulse. Increase the gap between pulses so all have returned before next one.
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How can the ultrasound image be made clearer (wavelength)?
Use shorter wavelength as they diffract much less, so the waves spread out less and can map the interfaces more precisely.
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What are the conditions for an object to be resolved?
The wavelength must be a similar size to the width of the object being resolved.
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What is the principle of superposition?
When two or more waves cross, the resultant displacement equals the vector sum of the individual displacements.
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What is the condition for interference to be noticeable?
The amplitudes of all the waves should be nearly equal.
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What are the conditions for waves from different sources to be coherent?
They must have the same wavelength and frequency and must have a fixed phase difference between them.
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When do you get constructive interference?
At any point where the path difference of the waves is a whole number of wavelengths as this means that they are in phase.
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When do you get destructive interference?
At any point where the path difference of the waves is an odd number of half wavelengths, as this means that the waves must be in antiphase.
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Under what conditions do stable interference patterns occur?
If the waves are of the same type, the sources are coherent and the waves have a similar amplitude at the point of superposition.
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How do standing waves form?
They are created by the superposition of two progressive waves of equal frequency and amplitude moving in opposite directions.
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How do standing waves differ from progressive waves?
Standing waves do not transmit energy. Also, the amplitude of a standing wave changes between nodes and antinodes, but is constant for progressive waves. Also phase varies continuously along a travelling wave.
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How can you demonstrate standing waves?
Attach a vibrating transducer at one end with the other end fixed. If the signal is altered so that an exact number of waves are produced in the time for the wave to be reflected, the original and reflected reinforce each other (at resonant freq).
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Where are nodes?
At points where the amplitude of the vibration is zero.
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Where are antinodes?
At points of maximum amplitude.
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What factors affect resonant frequencies?
A longer string = lower frequency as wavelength is longer. A heavier/looser string = lower frequency as the waves travel more slowly
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How do you increase the frequency for a string instrument?
Use a shorter string, use a string with greater tension and use a string that has a lower mass/unit length
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What form at open ends?
Antinodes
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What forms at closed ends?
Nodes as the particles are unable to oscillate.
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What is diffraction?
When waves pass around an object or through a gap, they spread out.
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What is Huygens' construction?
Every point on a wavefront may be considered to be a point source of secondary wavelets that spread out in the forward direction at the speed of the wave.
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How does the size of the shadow depend on the wavelength of the wave?
The wider the obstacle compared to the wavelength of the wave, the less diffraction you get, so the longer the shadow.
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When is diffraction most significant?
When the gap is the same size as the wavelength.
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How can you form diffraction patterns?
Shine a beam of light through a diffraction grating and a diffraction patter will be produced on a screen.
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What is the wavelength of purple light in the visible spectrum?
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What is the wavelength of red light in the visible spectrum?
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## Other cards in this set

### Card 2

#### Front

What is a traverse wave?

#### Back

A wave the oscillated perpendicular to the direction of propagation.

### Card 3

#### Front

What are mechanical waves?

#### Back ### Card 4

#### Front

What are the areas in a longitudinal wave?

#### Back ### Card 5

#### Front

What is amplitude?

#### Back 