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Physics > Waves > Flashcards

Waves Flashcards

1
Q

What is a wave?

A

Waves are vibrations that transfer energy through a medium without transferring matter.

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2
Q

What is refraction?

A

This is when light changes direction when crossing a boundary as a consequence of changing speed.

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3
Q

What is reflection?

A

This is when some of the wave travels back in the opposite direction after being bounced back from the boundary.

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4
Q

What is refraction?

A

This occurs when a wave spreads out after passing through a narrow gap.

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5
Q

What is phase difference?

A

It is the difference in displacement between two particles on the same wavefront or between two different waves.

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6
Q

What is a particle’s phase?

A

At a given period of time. is the fraction of a complete cycle that particle has completed since the start of the cycle.

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7
Q

What is the special property of em waves in a vaccum?

A

They all travel at the speed of light c

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8
Q

What are transverse waves? What are a few examples?

A

They are waves where the vibrations of their particles are perpendicular to the direction of propagation.Em waves, waves on string and s waves

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9
Q

What is a longitudinal wave? What are a few examples?

A

It is a wave where the vibrations of its particles are parallel to the direction of propagation.Sound waves, P waves

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10
Q

What is the difference between a displacement time and displacement distance graph?

A

The crest to crest distance is time period for displacement time.It is wavelength for displacement distance.

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11
Q

What are sound waves made up of?

A

They are made up of a series of alternate compressions and rarefactions in the medium they are travelling in.

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12
Q

How to find wavelength of longitudinal waves?

A

Measure the distance from compression to compression.

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13
Q

Describe the motion of a particle on a longitudinal wave?

A

It will go towards the compression coming from the left pass through it and move to the right and repeat.

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14
Q

Describe the motion of a particle on a transverse wave?

A

It will follow the motion of the particles before it.

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15
Q

What is polarisation?

A

This is when a transverse waves is passed through a filter so that its vibrations are contained to a single plane.

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16
Q

Mechanical waves vs em waves?

A

Mechanical waves require a medium in order to travel.Em waves do not.

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17
Q

Describe the polarising filter for a mechanical wave vs em wave?

A

For a mechanical wave vibrations parallel to the plane are allowed to pass through and this is the orientation of the filter.For em waves the filter is horizontal and vibrations perpendicular to the grill pass through.The parallel ones are absorbed.

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18
Q

What happens to light when it is reflected?

A

It is partially reflected.

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19
Q

How to plot a maul’s law graph?

A

It is a |cos x| graph of angle intensity against orientation.

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20
Q

How do polaroid glasses work?

A

Light from the sun is partially polarised when it reflects off water (horizontal plane).Polaroid glasses have a plane of polarisation at 90 degrees to the light, this reduces the glare protecting the eyes.

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21
Q

What is superposition?

A

This is when waves pass through each other and at the point they meet they combine together for an instant before they move apart.

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22
Q

What is the principle of superposition?

A

It states that when two waves combine together the resultant displacement of a point is equal to the sum of the individual displacements of that point.

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23
Q

What is constructive interference?

A

This is when a two crests/troughs combine together to produce an even larger crest/trough.This occurs when displacements are in the same direction.

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24
Q

What is destructive interference?

A

When a crest and trough cancel each other out.This occurs when their displacments are in different

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25
Q

When are two waves in phase and not in phase?

A

They are in phase when their phase difference is a multiple of 360.They are in anti-phase if their phase difference is an odd multiple of 180.

26
Q

How are stationary waves formed?

A

They from when two progressive waves of the same frequency and wavelength travelling in opposite directions superpose with each other.They transfer no energy.

27
Q

When are stationary waves formed on a string?

A

When an exact number of waves are produced in the time it takes for a wave to be transmit and be reflected back.This is called the resonant frequency where an exact number of half wavelengths occur on a spring.

28
Q

Describe the points on a stationary wave?

A

Nodes are points of zero displacement where destructive interference occurs.Anti nodes are points of max displacement where constructive interference occurs.

29
Q

How many wavelengths will the nth harmonic fit on a string? What will the frequency be?

A

n/2 wavelengths. n x frequency of first harmonic.

30
Q

How to measure a stationary wave using a microwave transmitter and a metal plate?

A

Transmit microwaves to a metal plate and they will get reflected off the metal plate.Use a probe and move in between to measure nodes and anti nodes.

31
Q

Describe how stationary sound waves are produced?

A

Connect a loudspeaker to a tube with powder in it.Increase the frequency and see the powder will move at the antinodes but stay staionary at the nodes.ee

32
Q

Describe an experiment to calcualte the effect of tension, u and l on the first harmonic of a spring?

A

Connect an oscillator to a signal generator.Attach the string to the oscillator and pass it over a pulley clamped to a table.Load up some masses on the string to make it taut.Measure mass per unit length tension and length.Alter frequency till you get first harmonic.Then vary the other variables and see how they change the frequency of the first harmonic.

33
Q

What is the formula for first harmonic and how does changing the variables affect the frequency?

A

f=1/2l root t/u increasing l reduces the resonant frequency. Increasing T increases frequency more taut.Increasing u the lower the resonant frequency. because waves travel slower down a heavy spring

34
Q

What different types of diffraction do you get when a wave passes through a gap?

A

When the size of gap is same size as wavelngth u get max diffraction.When it is a lot bigger you dont get much diffraction.When the gap is several wavelengths wide you get some diffraction.If the gap is smaller than the wavelength most waves get reflected back.

35
Q

What must be used in order to acheive a clear diffraction pattern?

A

A monochromatic, coherent source must be used.A monochromatic source emits light of a single wavelength so the amount of diffraction will be the same.

36
Q

What is a coherent light source?

A

It produces waves with constant frequency, constant wavelength and a constant phase difference.

37
Q

Why is laser light preferred?

A

It is monochromatic and a coherent source of light.

38
Q

What happens when you shine a single colour of light through a slit?

A

You get a central bright fringe maximum at the centre the same colour and then you get an alternating pattern of dark and bright fringes either side.

39
Q

Effect of changing wavelength or slit width on width of central max in single slit diffraction?

A

Increasing the slit width reduces amount of diffraction but intensity increases so central maximum is narrower but higher.Increasing wavelength increases diffraction so central max is wider but lower.

40
Q

Why is the central max the brightest part of the pattern?

A

The most photons per unit area are hitting the centre of the screen.The intensity is much higher.

41
Q

When are two sources said to be coherent?

A

This occurs when two sources produce waves of the same frequency, wavelength and the the waves must have a constant phase difference.

42
Q

What is path difference?

A

It is the distance one wave has travelled further than other.

43
Q

When does constructive and destructive interference occur between two sources?

A

This is when the path difference is n lambda or (n+1/2) lamba

44
Q

How to show constructive and destructive interference?

A

Connect two microphones to same signal generator and walk across the wall they are being transmitted at.

45
Q

What is the formula for the central max in single slit?

A

W=2lambdad/a a is slit distance d is distnce from screen to slit.

46
Q

What is the formula for fringe spacing in double slit?

A

w=lambda d/s. S is slit seperation and d is distance between slits and screen.

47
Q

Describe how to carry out young’s double slit experiment?

A

Shine laser light at a double slit it will produce an interference pattern on the screen.Measure distance between successive dark fringes and divide by n to get fringe seperation.Plot a gaph of w against d and find lamdba.

48
Q

What is a diffraction grating?

A

It contains a large number of equally spaced slits that are very close together.

49
Q

If the grating has n number of slits per mete whats the line spacing?

A

1/n.

50
Q

What does d in dsintheta=n lambda represent? What is a coarser grating?

A

Slit spacing. Fewer slits in given width.

51
Q

Use of a diffraction grating?

A

Can split up light from a star to produce a line absorption spectrum to see the light that has been absorbed can help identify elements of star as certain elements absorb different wavelenghts.

52
Q

What type of spectrum is a line absorbption and emission?

A

absorbption is a continuous specturum and emission is a spectrum consiting of coloured lines.

53
Q

Safety precuations when using a laser?

A

Keep away from eyes
Wear googles
Turn off when not required
Dont reflect light off anything.

54
Q

What is relative refractive index?

A

The refractive index of n2/n1.

55
Q

What some properties of optical fibres that prevent the signal to be lost?

A

The fibres are transparent to minimise light absorption.

Consists of a core surrounded by a cladding of lower n to allow TIR.

56
Q

Why must be the core be narrow?

A

It must be narrow to prevent light taking different parts hence to reduce modal dispersion.

57
Q

What is the function of the core?

A

It is there in order to prevent the core getting scratched which may lead to signal loss and it is there to prevent light crossing over from one fibre to another.

58
Q

What is modal dispersion?

A

This is when light entering the core takes different paths to travel to the end of the core.For example light that is being TIR will take longer to reach the end than light travelling along the transmission axis.This leads to pulse broadening as the information arrives at different times.Therefore a narrow core is needed so all the light takes the same path.Single mode fibre.

59
Q

What is material dispersion?

A

This occurs when the light entering a fibre is diffracted by different amounts due to it being made up of different wavelengths.Shorter wavelengths may take more time to reach the ened.Therefore use monochromatic light or use repeaters to boost the signal.

60
Q

What is dispersion?

A

This is when the signal amplitude is reduced and broadened.This could lead to broadened pulses overlapping each other and information being lost.

61
Q

What is absorption?

A

This is when the material absorbs the signal itself which reduces the amplitude of the signal.

Physics (19 decks)

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