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A LEVEL PHYSICS > Waves > Flashcards

Waves Flashcards

1
Q

State what is meant by monochromatic.

A

-Single wavelength (or frequency)

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2
Q

State what is meant by coherent.

A

-(waves/source(s) have) constant phase difference

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3
Q

The laser in a double slit interference test is replaced by another laser emitting visible light with a shorter wavelength.
State and explain how this will affect the spacing of the maxima on the screen. (2 marks)

A
  • Maxima will end up closer together

- Quote fringe spacing eq. spacing is proportional to wavelength so as wavelength decreases, fringe spacing decreases.

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4
Q

State TWO requirements for two light sources to be coherent. (2 marks)

A
  • Same wavelength or frequency

- Constant phase difference

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5
Q

Transverse waves:

A

oscillations are are at right angles to the direction of travel and energy transfer

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6
Q

Longitudinal waves:

A

oscillations are along the same direction as the direction of travel and energy transfer.

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7
Q

How to count up the number of maxima/lines produced?

A

Always treat the first maxima line as ZERO (0) then count up.
Eg if there is nine lines, total number would be 8 as first one is zero
(use trapezium rule y0 y1 analogy)

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8
Q

What do the symbols mean in fringe spacing eq :

w=(Lambda.D)s

A

Lambda- Wavelength

s: ‘The slit spacing’
w: All maxima added up and divided by the length (fringe spacing) e.g 8 maxima/0.16m = 0.020m

D: Distance from slits to screen (basically the laser length)

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9
Q

A narrow beam of monochromatic red light is directed at a double slit arrangement. Parallel
red and dark fringes are seen on the screen shown in the diagram above.

Describe how the appearance of the fringes would differ if white light had been used
instead of red light (3 marks)

A

-central (bright) fringe would be white (due to waves of all colours meeting at midpoint in same phase)
-(dark) fringes would be closer together because white light has a shorter wavelength
-bright fringes wider
(generally would form blue on LHS and red on RHS) due to white light containing all colours

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10
Q

State two ways in which the appearance of the fringes would change if the slit was made
narrower. (2 marks)

A
  • Wider/increased separation

- Lower intensity

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11
Q

Characteristics of white light used in a slit experiment:

A
  • Central bright fringe
  • Blue colour formed on far LHS maxima
  • Red colour formed on far RHS maxima
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12
Q

How to show that beams cannot be observed over a certain order:

A

dsintheta=nlambda
Solve for n and let sintheta = sin90
work out the value for n, e.g (1.67x10^-6xsin90/590x10^-9)
=2.83
Therefore 3rd order or higher isn’t possible

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13
Q

State and explain what happens to the value of angle θ for the first order beam if the
wavelength of the monochromatic light decreases (2 marks)

A
  • Angle gets smaller

- Because path difference gets smaller

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14
Q

what is d in dsintheta=nlambda

A

d=1/N(Number of slits per metre)

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15
Q

Describe the necessary procedure in order to obtain an accurate and reliable value
for the wavelength of the laser light.
Your answer should include details of all the measurements and necessary
calculations. (6 marks)

A
  • Use dsintheta=nlambda
  • Measure appropriate angle (first order beam minimum)
  • Protractor to measure angle
  • For accuracy, use protractor with 0.5degrees or less intervals
  • Obtain d by 1/Lines per mm x10^3 (x10x100)
  • Rearrange equation for lambda=dsintheta/n to obtain wavelength
  • Check/repeat for different distances (D)
  • Use spectrometer
  • Measure theta for different orders
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16
Q

Electromagnetic waves are similar in nature to wave A.(transverse)
Explain why it is important to correctly align the aerial of a TV in order to receive the
strongest signal. (2 marks)

A
  • (transmitted radio waves are often) polarised

- aerial must be aligned in the same plane (of polarisation) of the wave

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17
Q

Amplitude (2 marks)

A
  • The maximum displacement

- From the equilibrium position

18
Q

The wave travels to the right.
Describe how the vertical displacement of the knot varies over the next complete cycle (for transverse wave) (3 marks)

A continuous wave of the same amplitude and frequency moves along the rope from the
right and passes through the first wave. The knot becomes motionless.
Explain how this could happen. (3 marks)

A
  • (vertically) downwards
  • then upwards
  • down (¼ cycle) to equilibrium position
  • Stationary wave formed
  • By superposition
  • knot is at a node / waves always cancel where the node(knot) is
19
Q

When stating the characteristic features of waves, what should you mention?

A

The motions of oscillation towards direction of wave travel/ propagation/ energy transfer

20
Q

Other than electromagnetic radiation, give one example of a wave that is transverse.

A
  • Surface of water in ripple tank

- Rope

21
Q

Daylight passes horizontally through a fixed polarising filter P. An observer views the light
emerging through a second polarising filter Q, which may be rotated in a vertical plane
about point X
Describe what the observer would see as Q is rotated slowly through 360 (2 marks)

A
  • variation in intensity between max and min (or light and dark)
  • two maxima (or two minima) in 360° rotation
22
Q

State one application, other than in education, of a polarising filter and give a reason for its
use. (2 marks)

A

Camera: Reduces glare/enhances image

23
Q

Wavelength of a wave

A

Least distance between two adjacent vibrating particles with the same displacement and velocity at the same time

24
Q

Figure 1 represents a stationary wave formed on a steel string fixed at P and Q when it is
plucked at its centre.
Explain why a stationary wave is formed on the string ( 3marks)

A

-Progressive waves travel from the centre to the ends of the string (nodes) and reflect back
-two (progressive) waves travel in opposite directions along the string
-Superposition/(interference) occurs
(waves have same frequency,wavelength, and amplitude)

25
Q

A microwave transmitter directs waves towards a metal plate. When a microwave detector is
moved along a line normal to the transmitter and the plate, it passes through a sequence of
equally spaced maxima and minima of intensity.
Explain how these maxima and minima are formed. ( 4 marks)

A
  • Superposition occurs
  • Maxima formed where waves are in phase and interfere constructively
  • Minima formed where waves are out of phase and interfere destructively
  • WAVES REFLECT AT METAL PLATE * (results in waves travelling back in the opposite direction and superposing)
26
Q

Distance between adjacent nodes and distance between minima:

A

1/2pi radians

27
Q

When describing a stationary wave, what should you mention?

A
  • The number of nodes and say there is NO MOVEMENT/zero AMPLITUDE here
  • Antinodes: Where displacement is at maximum (both negative and positive ones) e.g 3 antinodes where displacement is maximum
28
Q

The figure below shows a stationary wave on a string. The string is tied onto a thin metal bar
at A and fixed at B. A vibration generator causes the bar to oscillate at a chosen frequency.

Explain how a stationary wave is formed. Then describe the key features of the stationary wave
shown in the figure above. (6 marks)

A

-Waves have same wavelength/frequency
-Waves reflect off clamp and the rod
-The waves that are travelling in opposite directions superpose/interfere
-Always cancellation (destructive) at nodes and constructive superposition at antinodes
-Energy isnt transferred along string
-Between node and antinode, amplitude of oscillation increases
For this string in particular:
-4 nodes where there is no movement/zero amplitude
-3 antinodes where displacement is maximum
-Wavelength is 0.8m
-Ends with antinodes in phase

29
Q

The guitarist needs to raise the fundamental frequency of vibration of this string.
State one way in which this can be achieved. (1 mark)

A

decrease the length/ tighten string

30
Q

Describe the motion of point X. ( a point midway down the antinode, (on the third quarter of the arch) => STILL CLASSED AS HALF A WAVELENGTH

A
  • Oscillates

- About EQUILIBRIUM position

31
Q

Can you get 3/4pi in phase difference calculaitons?

A

No, if a point is 3 quarters along an antinode it is still classed as pi/2

32
Q

State how you know that the wave on the string is transverse.

A

displacement perpendicular to rest position of the string

33
Q

Suggest an experiment that will demonstrate the wave nature of sound

A

Diffraction through a door

34
Q

Drawing a graph for light intensity of light of a greater wavelength

A
  • centre 2x as wide as subsidaries

- centre of subsidary maxi further away from the centre

35
Q

The red laser light is replaced by a non-laser source emitting white light.
Describe how the appearance of the pattern would change. (3 marks)

A
  • Bright white central fringe
  • Subsidary maxima composed of a colour spectrum
  • Bright fringes wider, dark fringes closer together due to white light’s smaller wavelength
36
Q

Musical concert pitch has a frequency of 440 Hz.
A correctly tuned A-string on a guitar has a first harmonic (fundamental frequency)
two octaves below concert pitch.
Determine the first harmonic of the correctly tuned A-string.

A

An octave is half the frequency, therefore if 2 octaves lower 440/2= 220 . 220/2 = 110Hz

37
Q

State two differences between stationary waves and progressive waves. (2 marks)

A
  • in stationary waves, there is no energy transfer along the wave,
  • stationary waves have nodes and antinodes but progressive waves do not

-in progressive waves, all points have the same amplitude (in turn),
in stationary waves, they do not

38
Q

State how you could make a string on a stringed instrument vibrate in this mode of vibration.

A
  • On a guitar string, LIGHTLY STOP IN CENTRE OF STRING

- And pluck

39
Q

Describe how you would investigate the variation of the fundamental frequency (first harmonic) of a string with its length.
State which variable(s) you would need to control and how you would do so.
You may wish to assist your account by drawing a diagram. (4 marks)

A
  • keeps tension or mass per unit length constant
  • way of measuring frequency or producing vibration of known f
  • way of measuring length (at resonance)
  • use of suitable graph (f vs 1/l or l vs 1/f) to display results
40
Q

Which of the following is correct for a stationary wave?

A Between two nodes the amplitude of the wave is constant.
B The two waves producing the stationary wave must always be 180° out of phase.

C The separation of the nodes for the second harmonic is double the separation of
nodes for the first harmonic.
D Between two nodes all parts of the wave vibrate in phase.

A

D

A LEVEL PHYSICS (13 decks)

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