4.4 Waves Flashcards by Bianca Faith Quiring

Define the term ‘progressive wave’

A wave which transfers energy from one place to another with a wave front which travels through the material (in contrast to stationary waves which don’t appear to move)

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What is a longitudinal wave?

Waves which the particles oscillate in the same direction as energy propagation
There are rarefactions (areas of low pressure) and compressions (areas of high pressure)

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What is a transverse wave? Give examples.

Waves where the particle oscillations are perpendicular to the energy propagation
eg. Electromagnetic waves

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Define frequency and give its units

The number of waves passing through a point per second
Hertz (Hz) or s^-1

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Define wavelength

The distance between two adjacent corresponding points on a wave

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Define amplitude

The maximum displacement of the wave from its equilibrium position

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How can you find out the time period of a wave using its frequency?

T=1/f

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What is the phase difference of a wave and what is it measured in?

The amount one wave lags behind another as a proportion of the wavelength
Measured in radians or degrees

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What do each of the ‘axes’ on an oscilloscope measure?

Vertical divisions=voltage/amplitude of the wave
Horizontal divisions=time(can be used to find time period and frequency)

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Define refraction

Refraction is when a wave bends at a boundary between two materials due to the difference in density causing it to speed up or slow down

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True or false: a wave can either be refracted or reflected at a boundary, but never both

False
At low angle of incidence most will be refracted, but some will reflect

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True or false: diffraction is most noticeable when the wavelength is much larger than the gap the wave is travelling through

False
The most diffraction is seen when the gap and the wavelength are the same size
If the wavelength is much bigger the waves will be mostly reflected

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Can all waves be polarised?

No, only transverse waves

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What is the difference between a polarised and unpolarised wave?

Polarised waves only contain waves oscillating along one axis
Unpolarised waves can be oscillating in any direction perpendicular to the axis of propagation

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Describe how a ripple tank might be used to investigate diffraction

Create water waves in the tank
Vary the size of a gap for them to pass through
Note how the direction of the waves passing through changes

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Polarised light is being passed through a rotating polarisation filter. What would happen to the intensity of the light passing through?

It would vary from a maximum (all light passes through) when the axis of polarisation and the axis of the filter line up to a minimum (no light passes through) when the axes are perpendicular

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How is intensity defined in terms of power?

Intensity is power/area

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How are intensity and amplitude related?

Intensity is proportional to amplitude ^2

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True or false: all electromagnetic waves have the same time period

False
They all travel at the same speed - but their wavelengths,frequencies and time periods vary

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How fast do electromagnetic waves travel in a vacuum?

3 x 10^8 m/s (the speed of light)

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True or false: the magnetic field and electric field in a electromagnetic wave are parallel to each other

False
The electric and magnetic field are at right angles to each other

Put the following in order from highest to lowest frequency: x-rays, radio, microwaves, UV, visible

X rays
UV
Visible
Microwaves
Radio

Which type of EM radiation has a wavelength of approximately 1 micrometer?

Infrared is between 700 nm and 1mm

What is the range of wavelengths commonly known as visible light?

300-700nm

True or false: microwaves can be polarised using a metal grid rather than a polarising filter

True- this is because the wavelength of microwaves is sufficiently large than the grid works as a Polarising filter

What is meant by the refractive index of a material? What equation can be used to find it?

The refractive index is a measure of how fast light travels in a material compared to its speed in a vacuum n=c/v refractive index=speed of light/velocity in the material

A beam of light is shone at a boundary between air and glass. As the angle of incidence is increased from 0 to 90, what would you see?

At 0 all of the light would pass into the material along the normal The light would then be seen to be refracted ( the angle to the normal on the glass would be larger than the incident angle) Eventually the light would bend so much it would start to be reflected back

What is the name given to the angle of incidence at which the light will reflect off a boundary rather than refracting in the medium?

The critical angle SinC=1/n

What is the name given to what happens to light at angles greater than the critical angle?

Total internal reflection

Waves can superpose, what does this mean?

Two waves in the same place (ie. One on top of the others) will combine

What are the two types of interference?

Constructive and destructive

Describe an experiment to investigate the principle of superposition using sound

-use two speakers, a moderate distance apart, connected to the same signal generator to transmit sound waves -walk along a line perpendicular to the speakers-you should hear alternating loud and quiet points -in some places the waves from each speaker constructively interfere(loud) and in some places it’s destructive

Define coherence

Waves with the same frequency and wavelength and a fixed/constant phase difference

If two waves are in phase will they constructively or destructively interfere?

Constructively

True or false: path difference and phase difference are two names for the same thing

False Path difference is the difference in distance that two waves have travelled in terms of the wavelength (units of length) Phase difference is the difference in the point in the cycle of two waves as a proration of a full wave cycle (units of degrees/radians)

Why is a laser useful in showing interference and diffraction

It produces monochromatic (same wavelength/colour) light

What is Young’s double slit experiment?

A single source of light directed towards a double slit, which creates two coherent beams of light. This interferes as it hits the screen and creates an interference pattern

Describe the interference pattern created using white light

The interference pattern would be a repeating coloured spectrum along the screen, with a bright white point directly in front of the slit

Increasing the slit width increases the width of the central diffraction maximum. True or false?

True

Wha equation relates the wavelength of light to the slit spacing and distance to the screen

Wavelength=(slit spacing x fringe spacing)/ distance to screen

Which two properties of light can only be explained if it is a wave?

Diffraction Interference

When shining light through a diffraction grating there is a maximum number of fringes which would be produced. How would you find this maximum number?

n(lambda)=Dsin(theta) use theta=90 rearrange for n

What is a stationary wave?

Stationary waves consist of alternating fixed pattern of nodes (points with zero amplitude) and antinodes (points with maximum amplitude). No energy is transferred across the wave

What is a node?

A point with no vibrations in which the resultant amplitude is 0

What is an antinode?

A point with maximum vibration in which the resultant amplitude is at maximum

Hat are the conditions for a stationary wave to be produced?

-the waves must be coherent -they must be travelling in opposite directions These conditions are often met when a wave is reflected back onto itself

Give an example of an experiment you could do to show a stationary wave

Use an oscillator to pass a wave along a string which is fixed at one end The stationary wave will form when the progressive wave is reflected off the fixed end

Give a similarity and difference between stationary waves and progressive waves?

S: both have wavelength, frequency and amplitude D:stationary waves don’t transmit energy from one place to another

How could you use the formation of stationary waves in a resonance tube to find this speed of sound?

-create a closed end pipe using a hollow pipe inside a measuring cylinder containing water -using a tuning fork (producing known frequency) and hold it above the tube -move the tube up until you find the first position which causes resonance T his length will be a quarter of the wavelength -speed=frequencyxwavelength

What is meant by harmonics?

Harmonics are points where the stationary wave form doesn’t change because the waves in each direction are reinforcing each other

A stationary wave on a string is made to oscillate at its fundamental frequency (1st harmonic)-how many nodes and antinodes would you see?

Nodes- 2 (1 at either end) Antinodes- 1 (in the middle)