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Physics > Waves > Flashcards

Waves Flashcards

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1
Q

What is meant by monochromatic?

A

Single wavelength and frequency

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2
Q

What is meant by coherent?

A

Single wavelength and frequency and a constant phase difference

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3
Q

Describe the pattern on an intensity-position on the screen graph of the fringes in Young’s Double Slit Experiment

A

Maxima all of similar intensity to central maximum and all fringes same width as central fringe

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4
Q

Describe the appearance of fringes in a double slit arrangement of red light is used

A

Parallel red and dark fringes are seen on the screen

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5
Q

Describe the appearance of fringes in a double slit arrangement of white light is used

A

Central fringe is white and outer fringes would be blue on inner side and red on outer side

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6
Q

Describe the single slit diffraction pattern plotted on an intensity-position on screen graph

A

Intensity decreases as you move away from central maxima and all fringe widths equal

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7
Q

How would a fringe pattern change if light of a longer wavelength is used?

A

Maxima further apart and wider

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8
Q

What happens to the angle theta for the first order beam if the wavelength of monochromatic light is increased?

A

Increases

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9
Q

If a light ray travels from a higher refractive index to a lower refractive index, which way does the light bend?

A

Away from the normal

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10
Q

If a light ray travels from a lower refractive index to a higher refractive index, which way does the light bend?

A

Towards the normal

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11
Q

What conditions can Total Internal Reflection take place in?

A

When light ray travels from higher n to lower n, and angle of incidence is above critical angle

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12
Q

What is the inner part of an optical fibre?

A

Core

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13
Q

What is outer part of an optical fibre?

A

Cladding

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14
Q

Give two advantages of having a smaller diameter core in an optical fibre?

A

Less light lost, better quality signal (less distortion)

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15
Q

Why is the core of an optical fibre made as small as possible?

A

To reduce multi-path dispersion which causes light to travel at different angles and arrive at different times

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16
Q

Give one application of optical fibres and how it benefitted society

A

Broadband internet, high speed internet

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17
Q

Why is cladding needed in optical fibres?

A

To maintain a quality pulse and to keep the pulse in the core through total internal reflection

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18
Q

Explain why pulses are broader and have lower amplitude after travelling through optical fibres

A

Reduced amplitude due to energy loss in fibre, pulse broadening due to multi-path dispersion

19
Q

Give two properties of light produced by a laser

A

Monochromatic and coherent

20
Q

Explain how cladding improves the security of data travelling in optical fibres

A

Cladding prevents light in the fibre from moving between fibres and without the cladding, scratches in the core would allow light to travel between fibres

21
Q

Why do aerials need to be correctly aligned to get the best signal?

A

Transmitted radio waves are often polarises meaning aerial rods must be aligned in the same phase

22
Q

Define the amplitude of a wave

A

Maximum displacement of any point on the wave from the equilibrium position

23
Q

Give two examples of progressive waves other than EM waves

A

Water waves, rope

24
Q

Give a use of polarising filters

A

Sunglasses, to reduce glare

25
Q

Give two properties of reflected waves which produce stationary waves

A

Waves have same frequency and amplitude

26
Q

What happens when waves travel through each other in opposites directions?

A

Interference/superposition

27
Q

What happens at nodes?

A

Destructive interference / cancellation

28
Q

What happens at anti noses?

A

Constructive interference / reinforcement

29
Q

Give three properties of stationary waves

A

Nodes, antinodes, do not transfer energy

30
Q

How do you raise the fundamental frequency of vibration of a string?

A

Decrease length or increase tension of string

31
Q

What is the path difference of waves in phase?

A

0, one full wavelength, two full wavelengths etc

32
Q

What is the path difference of waves in antiphase?

A

One half wavelength, one and a half wavelengths etc

33
Q

If two waves have a path difference, what does this mean?

A

They travel different distances

34
Q

For constructive interference to occur, what must the path difference be of two waves?

A

m x wavelength (where m is the number of maxima from the central maxima)

35
Q

For destructive interference to occur, what must the path difference be of two waves?

A

(m + 1/2) x wavelength (where m is the number of maxima from the central maxima)

36
Q

In Young’s Slits experiment, explain why the intensity of minima is never zero as you move outwards?

A

Waves which form minima always travel different distances and intensity decreases with distance

37
Q

At what angle to the direction of polarisation will a wave be completely blocked?

A

90 degrees, 270 degrees..

38
Q

Why may stationary waves only of specific frequencies be able to form on a wire?

A

If the wires ends are fixed (as they have to be nodes)

39
Q

How could you increase the pitch of note?

A

Raise tension in / decrease length of string

40
Q

Explain modal/multi path dispersion

A

Occurs in a wide core because light travelling along the axis of the core travels a shorter distance per metre of fibre than light that repeatedly undergoes TIR, causing a pulse to become longer

41
Q

Explain material / spectral dispersion

A

Occurs when white light is used because speed of light in glass of optical fibre depends on wavelength of light travelling through it e.g. blue light travels slower than red light due to lower wavelength (higher refractive index)

42
Q

Explain two changes to reduce material / spectral dispersion

A

Use monochromatic light so speed constant or use more repeaters so pulse is reformed before significant dispersion occurs

43
Q

In experiments to determine the fundamental frequency of a string at different tensions, explain why predicting frequencies at higher tensions may be incorrect?

A

At higher tensions, strong would stretch meaning its volume and mass per unit length would decrease

Physics (14 decks)

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