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Physics A-level > Waves > Flashcards

Waves Flashcards

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1
Q

What is a mechanical wave and give one example.

A

Requires a medium to transfer through, and an examples are sound waves and seismic waves.

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2
Q

What is an electromagnetic wave and give an example.

A

Examples include light, radio waves microwaves and x rays.

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3
Q

What are the 2 main types of waves? What differentiates them?

A

Transverse and longitudinal, transverse waves have an oscillation parallel to its direction. Longitudinal waves have an oscillation parallel to its direction.

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4
Q

Name 2 properties unique to a longitudinal wave?

A

Compressions and rarefractions.

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5
Q

What is phase difference measures in?

A

In degrees, one wavelength is 360 degrees.

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6
Q

How are standing waves formed?

A

When two waves pass through eachother.

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7
Q

What is the equation for phase difference?

A

(2pi x distance)/ lambda

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8
Q

How does polarisation work and how and which category of waves can undergo this?

A

Polarisation is when a filter is applied in a specific plane (eg horizontal and vertical) and this filters out vibrations that cannot fit through the plane. This can only occur in transverse waves as longitudinal waves oscillate back on forth so they will be able to get through regardless.

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9
Q

What are the practical uses of polarisation?

A

Sunglasses and antenna in houses so they only pick up certain frequencies.

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10
Q

What are two properties of a stationary wave?

A

Nodes and antinodes as they are fixed in place.

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11
Q

Define superposition. (n x lambda)

A

When waves are in phase and they are interfere for the following wave to have a bigger amplitude.

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12
Q

Define destructive interference. And when can maximum destructive interference occur? ((n +1/2) x lambda)

A

When waves are out of phase and they interfere with eachother and cancel eachother out, maximum destructive interference can be achieved when the waves are 1/2 a cycle out of eachother.

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13
Q

Describe what happens when a white light is shone through a double slit.

A

The central maxima is white light and then the there are surrounding minimas (where light does not show) and then all the colour (violet –> red) of the visible light spectrum is shown.

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14
Q

Define refraction.

A

When a wave speed changes going from one medium to another. (more dense –> less dense means that the wave slows down)

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15
Q

Describe all the things that happen when light rays enter a more optically dense medium.

A

-Speed decreases
-Wavelength decreases
-Frequency remains constant
-Light rays bend towards normal

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16
Q

Define diffraction.

A

The spreading of waves when they pass through a gap

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17
Q

Define monochromatic.

A

A single colour of one wavelength.

18
Q

Define collumnated.

A

When light rays are (approx) parallel.

19
Q

What is (approx) the refractive index of air?

A

1

20
Q

What is (approx) the refractive index of glass?

A

1.5

21
Q

What is (approx) the refractive index of water?

A

1.33

22
Q

How do you find the speed of a wave inside a medium? (mention refractive index)

A

The speed of light in a vacuum divided by the refractive index.

23
Q

What does a high refractive index mean.

A

It means that light travels slower in the medium. (more optically sense)

24
Q

What is snells law?

A

n1 x sin01= n2 x sin02

25
Q

What is total internal reflection?

A

This is the reflection of waves back inside a medium at a boundary

26
Q

Partial reflection is at its greatest when…

A

The angle from the incident to the barrier is shallow.

27
Q

Define critical angle.

A

The angle of incidence that results in light being refracted along the boundary.

28
Q

How do you find the critical angle.

A

n1 x sin0c = n2 x sin90 (sin90 = 1)
sin0c = n1/n2

29
Q

State the structure of an optical fibre and explain.

A

-Glass core: Has a high enough refractive index so total internal reflection can take place.
-Cladding: Low refractive index so total internal reflection can take place.
-Protective plastic: To physically protect the optical fibre from scratches and damage.

30
Q

State the advantages and disadvantages of optical fibres.

A

Advantages:
-multiple frequencies can be sent down one fibre
Disadvantages:
-material dispersion
-modal dispersion

31
Q

Explain material dispersion.

A

This is when different wavelengths travel at different speeds and this causes the signal to spread out, causing pulse broadening.

32
Q

Explain modal dispersion.

A

This is when rays of light take different paths causing the pulse recieved to become broader which decreases signal. (This becomes even more significant in multimode fibres)

33
Q

What is a coherent source?

A

A coherent source is when a wave has the same frequency and wavelength and a CONSTANT phase difference

34
Q

What is the definition of superposition?

A

When two waves of the same type overlap and interact, the displacement of the medium (the amplitude) where the two waves overlap is the vector sum of the two displacements.

35
Q

What occurs when the angle of incidence is equal or less than the critical angle?

A

Only some light is reflected,total internal reflection does not occur.

36
Q

What occurs when the angle of incidence is equal to the critical angle?

A

Total internal reflection begins to occur, some light is reflected along the boundary.

37
Q

What occurs when the angle of incidence is greater than the critical angle?

A

Total internal reflection occurs.

38
Q

What is pulse broadening?

A

This is when the the duration of a pulse increases as a result of dispersion in an optical fibre.

39
Q

How is a stationary wave formed?

A

This can occur when a wave is formed by the superposition of two progressive waves of the same frequency and amplitude travelling in opposite directions.

40
Q

What is interference?

A

This is the superposition of waves from two coherent sources of waves.

41
Q

What is constructive interference?

A

This is interference when the waves are in phase.

42
Q

What is destructive interference?

A

This is interference when the waves are 180 degrees out of phase.

Physics A-level (6 decks)

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