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Xaverian Physics > Module 4 Basic Wave Properties / Refraction > Flashcards

Module 4 Basic Wave Properties / Refraction Flashcards

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1
Q

What is a progressive wave?

A

a wave which transfers energy from a source through the means of oscillations without the transfer of the medium

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2
Q

What are the two types of progressive waves?

A

Longitudinal and transverse waves

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3
Q

What is a longitudinal wave? Give an example

A

a wave where the particle vibrations are parallel to the direction of energy transfer
eg sound, ultrasound

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4
Q

What is a transverse wave? Give an example

A

A wave where the vibrations are at 90 degrees to the energy transfer
eg all electromagnetic waves; water waves

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5
Q

What waves can travel through a vacuum?

A

Electromagnetic waves

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6
Q

What is displacement?

A

Distance of a point on a wave above or below the undisturbed position - how much a point has moved from it’s rest position (y-axis)

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7
Q

Amplitude

A

Maximum displacement of a wave from it’s undisturbed position. Symbol A

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8
Q

What is wavelength?

A

Distance between two adjacent points in a phase

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9
Q

Symbol for wavelength

A

λ, units in metres

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10
Q

State 2 properties of sound waves

A

Longitudinal
and
Mechanical (need a medium to travel through)

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11
Q

What is the time period of a wave?

A

time taken for one complete oscillation or wavelength to pass a point

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12
Q

Symbol for time period

A

T - unit seconds

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13
Q

What is the frequency of a wave?

A

The number of wavelengths per unit of time

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14
Q

What are the crest and trough?

A

crest is the peak and trough is the dip in a snapshot of a transverse wave

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15
Q

What is rarefaction?

A

part of a longitudinal wave where the particles are the most spaced apart

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16
Q

What does the wave speed depend on?

A

the medium it is travelling through

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17
Q

Derive the wave equation

A

Speed = distance/time = λ/T
f=1/T
λx1/T=λf
speed = λf

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18
Q

What is an oscilloscope?

A

an apparatus which shows the amplitude of a wave on the y and x axis represents time

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19
Q

What is the unit used for the y-axis on an oscilloscope

A

volts

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20
Q

What does CRO stand for?

A

cathode ray oscilloscope (usually just called an oscilloscope)

21
Q

How is amplitude displayed on an oscilloscope?

A

Biggest value on the y-axis (in volts )
Count number of vertical squares from central line then multiply by voltage setting

22
Q

How to get time period from oscilloscope

A

Count the number of squares horizontally for one complete wavelength
Multiply by the timebase
(which is number of seconds per horizontal division)

23
Q

If the depth in a ripple is reduced what happens to the wave speed?

A

reduces wave speed

24
Q

Suggest a method of observing reflection

A

Visible light and a mirror - a wooden plank in a ripple tank

25
Q

Definition of intensity

A

the radiant power passing through a surface per unit area

26
Q

What is the unit for intensity?

A

Wm^-2

27
Q

Equation for intensity?

A

I=P/A

28
Q

What properties does intensity have in reference to distance?

A
  • As a wave travels from the source the radiant power spreads out and therefore decreases
  • From a point power spreads in all directions
  • To find the light intensity at a curtain distance, the area is equal to the area of a sphere
    Note: intensity is proportional to one over the square of the distance = inverse proportion - I ∝1/r^2
29
Q

What is the relationship between amplitude and intensity?

A

Intensity ∝ Amplitude^2

30
Q

Definition of refraction

A

change in speed of a wave as it passes from one medium to another causing a change in direction

31
Q

What is the refractive index?

A

the ratio of speed of light in a vacuum over speed of light in a medium

32
Q

Which direction are lightwaves refracted by when passing through medium when going from less to more dense?

A

towards the normal (when going from less to more dense)

33
Q

What happens when light crosses the boundary of two different mediums along the normal?

A

no change in direction but the light changes speed

34
Q

What is the relationship between n and the angle of refraction?

A

greater the index the smaller the angle

35
Q

What effects are there when two refractive indices are equal?

A

ray of light continues along it’s original pathway

36
Q

What stays the same during refraction?

A

frequency

37
Q

What happens if the angle of incidence is the critical angle?

A

refracted light travels along the boundary of the two media (angle of reflection = 90º)

38
Q

How are wavelength and amount of refraction related?

A

as wavelength decreases amount of refraction which takes places increases (ie bigger change in direction)

39
Q

What is Snell’s law?

A

nsin(θ)=constant

40
Q

Describe how the refractive index, and thus the critical angle of glass (to air) can be calculated using a RECTANGULAR glass block

A
  • Place the block of glass on a sheet of paper and draw a trace around the block
  • Draw a normal at a given point on the side of a block
    -Point a laser at this point, and using a protractor, measure the angle of incidence
    -Draw a dot where the beam of light exits the glass block and join the dot between entrance and exit
    -Measure the angle to the normal inside the block - this is angle of refraction
  • use nsin(θ)=constant (with n=1 for glass) to find refractive index for glass
  • then use sin(C) = 1/n to find critical angle C
41
Q

How can the critical angle be found using a semicircular glass block

A

-Place block on a piece of paper and trace

-Shine a laser/light ray at the curved side so that it is at right angles to edge

-vary the angle of incidence by adjusting the light ray until the beam refracts along the straight edge

-Mark the direction, and thus the angle of incidence of the light ray

42
Q

List wave phenomena for transverse waves

A

Reflection
Refraction
Interference
Diffraction
Polarisation

43
Q

List wave phenomena for longitudinal waves

A

Reflection
Refraction
Interference
Diffraction

44
Q

If two points are separated by half a wavelength, comment on their displacement

A

Same magnitude of displacement but travelling in opposite directions
(positive and negative values)

45
Q

If the phase difference between two points is 270 degrees, how far apart are the points?

A

3/4 wavelength apart

(270 degrees is 3/4 of 360)

46
Q

What is phase difference

A

the angle by which a wave lags or leads another

sometimes used to compare two points on the same wave

47
Q

what is the phase difference of two points separated by a whole wavelength?

A

360 degrees or 2pi radians

48
Q

what is the phase difference of two points separated by a half wavelength?

A

180 degrees or pi radians

Xaverian Physics (18 decks)

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