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Physics AS Rafa > 4.4 Waves > Flashcards

4.4 Waves Flashcards

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1
Q

How can you tell electromagnetic waves carry energy?

A
  • things heat up
  • ionisation
  • loud sounds cause large oscillations in air partials which can make things vibrate
  • wave power can be used to generate electricity
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2
Q

Define displacement.

A

How far a point on the wave has moved from its undisturbed - it can be positive or negative.

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3
Q

Define amplitude.

A

Amplitude is the maximum displacement - the distance from a peak to trough to the mean (rest) position.

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4
Q

Define wavelength.

A

The distance between two successive identical points that have the same pattern of oscillation. The distance a wave travels before it repeats itself.

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5
Q

Define period.

A

The time it takes for one complete cycle of oscillation go take place at any point.

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6
Q

Define phase difference.

A

Measured in radians. The amount one wave lags behind the other -the relationship between the pattern of vibration at two points.

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7
Q

Define frequency.

A

The number of oscillations per second passing a given point.

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8
Q

Equation for frequency.

A

Frequency = 1/Time

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9
Q

Equation for speed of wave (v).

A

Speed of wave (v) = frequency (f) x wavelength (y)

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10
Q

What is intensity?

A

A measure of how much energy a wave is carrying

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11
Q

Define progressive wave.

A

A type of wave that travels through a substance or space, carrying energy via the oscillation of particles

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12
Q

Define transverse wave.

A

A type of wave in which oscillations occur at right angles to the direction of wave propagation.

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13
Q

Define longitudinal wave.

A

A type of wave in which oscillations occur parallel to the direct of wave propagation.

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14
Q

Define coherence.

A

Constant phase difference.

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15
Q

Why is it difficult to produce coherent light waves?

A

It is difficult to control the frequency.

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16
Q

Equation for fringe spacing?

A

X=(wavelength x D)/ a (spacing between slits)

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17
Q

What is the equation for intensity?

A

Power/area

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18
Q

What’s intensity measured in?

A

Wm^-2

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19
Q

What do all electromagnetic waves have in common?

A
  • speed
  • transverse
  • can be refracted, reflected, diffracted and can undergo interference
  • their progressive waves carry energy
  • can be polarised
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20
Q

Wavelength of radio waves.

A

10^-1 to 10^6

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21
Q

Wavelength of microwaves.

A

10^-3 to 10^-1

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22
Q

Wavelength of infrared waves.

A

7x10^-7 to 10^-3

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23
Q

Wavelength of visible light.

A

4x10^-7 to 7x10^-7

24
Q

Wavelength of UV waves.

A

10^-8 to 4x10^-7

25
Q

Wavelength of X-rays

A

10^-13 to 10^-8

26
Q

Wavelength of gamma rays.

A

10^-16 to 10^-10

27
Q

What happens if the second polarising filter is rotated by 45 degrees?

A

The intensity will be half that getting through the first filter.

28
Q

When do you get the most diffraction?

A

When the gap is the same size as the wavelength.

29
Q

What does refractive index measure?

A

How much a material slows down light.

30
Q

What is the absolute refractive index of a material?

A

The ratio between the speed of light in a vacuum and the speed of light in that material.

31
Q

Equation for refractive index.

A

N = c/ v

32
Q

What does snells law do?

A

Uses angles to calculate the refractive index.

33
Q

What is snells law?

A

N1sinø1 = n2sinø2

34
Q

What happens to the angle of incidence when the angle of refraction is a right angle?

A

The angle of incidence is critical.

35
Q

What happens to snells law for light hitting a material to air boundary?

A

Sin c = 1/n

36
Q

What happens to the wavelength when the pip has a closed end?

A

It is a quarter wavelength.

37
Q

What are progressive waves?

A

Waves that transfer energy away from a source, via oscillations of particles

38
Q

How many radians is a full cycle of a wave?

A

2pi

39
Q

Define intensity.

A

Rate of flow of energy per unit area at right angles to the direction of travel of the wave. Measured in Wm-2.

40
Q

What is the refractive index of air?

A

1

41
Q

Define interference.

A

When two waves superimpose at a point there is a change in overall displacement.

42
Q

What is a node?

A

Occurs where amplitude/displacement is always 0

43
Q

What is an antinode?

A

Occurred where the amplitude takes the maximum possible value

44
Q

Big equation for intensity

A

(Energy/time)/area

45
Q

How are intensity and amplitude related?

A

I=A^2

46
Q

What is a plane polarised wave?

A

We’re all oscillations of the field and the direction of travel are confined to a single plane

47
Q

What is a polarising filter?

A

Produces plane polarised light by selective absorption of one component of the incident oscillations - only component of light polarised perpendicular to that direction

48
Q

What are differences between standing and progressive waves?

A

Progressive waves transfer energy,
all points on a progressive wave have different phase (in one λ),
stationary wave traps energy in pockets,
stationary wave has nodes and antinodes

49
Q

What is unique about EM waves?

A

They travel at c (310^8) in a vacuum

50
Q

When you double the frequency what happens to the speed of a wave, and the speed of oscillation of an individual point on a wave?

A

The wave speed will not change, the wavelength will just halve proportionally.
For an individual point, it will oscillate twice as many times in a second and so it’s speed doubles

51
Q

What happens to intensity if amplitude is doubled?

A

Increased by a factor of 4

52
Q

What happens to intensity and position if separation is halved?

A

Intensity unchanged

Distance doubles

53
Q

What happens to intensity and position of they become 180 out of phase?

A

Intensity unchanged

Maxima move to minima

54
Q

Define diffraction

A

Oaths spreading out after gal or around an obstacle

55
Q

Define intensity

A

The incident energy per unit area per second

56
Q

What are the conditions necessary to produce visible fringes?

A 
Coherent source
Constant phase relationship
Slits must be close together 
Similar amplitude
Similar intensities
57
Q

Define diffraction

A

Wavefronts spreading after passing through a gap or around an obstacle

Physics AS Rafa (12 decks)

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