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Physics > Chapter 11 - Waves > Flashcards

Chapter 11 - Waves Flashcards

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1
Q

What are P waves and S waves?

A

Primary and secondary waves

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2
Q

What is a progressive wave and what do they transfer?

A

An oscillation that travels through matter but only transfers energy

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3
Q

What happens when a progressive wave travels through a medium?

A

The particles move from their original equilibrium post into a new position
The particles exert forces on each other so a displaced particle experiences a restoring force which brings it back to its original position

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4
Q

What is a transverse wave?

A

A wave in which the oscillations are perpendicular to the direction of energy transfer

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5
Q

What do peaks and troughs in a transverse wave show?

A

It shows where the particles are at a maximum displacement from their equilibrium position

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6
Q

What are some examples of transverse waves?

A

Waves on the surface of water
EM waves
S waves in earthquakes
Waves on stretched strings

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7
Q

What is a longitudinal wave?

A

A wave in which oscillations are parallel to the direction of energy transfer

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8
Q

What are some examples of longitudinal waves?

A

Sound waves

P waves in earthquakes

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9
Q

What are compressions and rarefactions?

A

Similar to peaks and troughs but are instead created by longitudinal waves (compression)

The particles are displaced and bounce off each other

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10
Q

What is displacement?

A

Distance from equilibrium position

Unit - m

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11
Q

What is amplitude?

A

Maximum displacement from equilibrium position

Unit - m

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12
Q

What is wavelength?

A

Minimum distance between two points in phase

E.g - from one peak to another or one trough to another

Unit - m

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13
Q

What is period of oscillation?

A

Time taken for one oscillation or one wavelength to pass a point

Unit - s

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14
Q

What is frequency?

A

Number of wavelengths passing a point per unit time

Unit - Hz

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15
Q

What is wave speed?

A

Distance travelled by the wave per unit time

Unit - ms^-1

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16
Q

What is the wave equation?

A

Wave speed = Frequency x Wavelength

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17
Q

What is a wave profile and what does it show?

A

A graph showing the displacement of the particles in the wave against the distance along the wave.

(A snapshot of the wave)

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18
Q

What can the wave profile be used for?

A

Determine the wavelength and amplitude of both types of wave

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19
Q

How do you work out where a particle will move from a wave profile?

A

Don’t move the particle but move the wave the particle will follow the peaks and troughs.

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20
Q

What is phase difference?

A

The difference between the displacements of particles along the wave or the displacements of particles in different waves.

It is measured in degrees or pi radians.

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21
Q

What does it mean when two particles are in phase?

A

They both reach maximum positive displacement at the same time.

They have a phase difference of 0

22
Q

How do you describe two particles that are separated by a distance of one whole wavelength?

A

Phase difference of 2pi or 360 degrees

23
Q

What does it mean when two particles are in antiphase?

A

One reaches maximum positive displacement as the other reaches maximum negative displacement

They have a phase difference of pi or 180 degrees

24
Q

What is another type of graph showing waves (not wave profile) and what can it be used to determine?

A

Displacement time graph which shows how displacement of a particle varies as time changes

It can be used to determine the period and amplitude of both types of waves

25
Q

What is reflection?

A

Reflection occurs when a wave changes direction at a boundary between two different media and remains in the original medium

Wavelength and frequency do not change

26
Q

What is the law of reflection?

A

It states that the angle of incidence = angle of reflection

27
Q

What is refraction?

A

Refraction occurs when a wave changes direction as it changes speed when it passes from one medium to another

Whenever a wave refracts there is always a partial reflection

Doesn’t change frequency but if the wave slows down then wavelength decreases

28
Q

What happens if the wave slows down or speeds up at the boundary between two media?

A

Slows down - Refract towards the normal

Speeds up - Refracts away from the normal

29
Q

What happens to sound and EM waves in a denser medium?

A

Sound waves speed up in a denser medium

EM waves slow down in a denser medium

30
Q

What happens when water waves enter shallower water?

A

They slow down and the wavelength gets shorter

31
Q

What is diffraction?

A

When waves travel through a gap or around an obstacle they spread out

Speed, wavelength and frequency do not change

Same gap and wavelength size means more diffraction

32
Q

What is polarisation?

A

Make the particles of a wave oscillate along one direction only

Longitudinal waves cannot be plane polarised as they are already limited to one plane

33
Q

What is partial polarisation?

A

When tranverse waves reflect off a surface and there are more waves oscillating in one plane compared to the other

34
Q

What is the intensity of a wave?

A

The radiant power passing through a surface per unit area

35
Q

What is the equation for intensity and what are its units?

A

Intensity = Power passing through surface / Cross sectional area of surace

Units - Watts per square metre

36
Q

How do you work out intensity at a distance from the source?

A

Intensity = Total radiant power / 4 pi r squared

r = distance from source

37
Q

What is the relationship between intensity and distance from the source?

A

Distance is inversely proportional to the square of intensity

(Double distance means intensity decreases by 2 squared which is 4)

38
Q

What is the relationship between intensity and amplitude?

A

Intensity is directly proportional to the square of the amplitude

Double amplitude and intensity will quadruple

39
Q

Do EM waves need a medium?

A

No they can travel through a vacuum

40
Q

What is the electromagnetic spectrum?

A

In order of reducing wavelength (m)

10^6 - Radio Waves
10^-1 - Microwaves
10^-3 - Infrared
7x10^-7 - Visible
4x10^-7 - Ultraviolet
10^-8 - X rays
10^-10  - Gamma rays
41
Q

What is the speed of an EM wave through a vacuum?

A

3x10^8 ms^-1

42
Q

What is a polarising filter and why do we use it?

A

Most natural EM waves are unpolarised so the electric field oscillates in random planes 90 degrees to the energy transfer.

Each filter only allows waves with a particular orientation through

43
Q

What does a horizontal polarising filter do?

A

Horizontally polarises EM waves. (It is drawn with vertical bars)

44
Q

What is the real world use of polarising filters?

A

Sunglasses
In order to reduce interference in communications transmitters some are polarised vertically and other are polarised horizontally

45
Q

What is a refractive index?

A

The relative speed at which light travels through the medium compared to the light at which light travels through a vacuum

46
Q

What is the equation for refractive index?

A

Refractive Index = Speed of light through vacuum(3x10^8 m^s-1) / Speed of light through material

Refractive Index has no units

47
Q

What equation describes what happens when light travels from one medium to another?

A

n1 sinθ1 = n2 sinθ2
n=refractive index
θ= Angle between the normal and the incident ray

48
Q

What is total internal reflection?

A

When the light strikes the boundary at a large angle to the normal, it is totally internally reflected and no light is refracted out of the medium

49
Q

What are the two conditions required for total internal reflection?

A

The light must be travelling through a medium with a higher refractive index as it strikes the boundary with a lower refractive index

The angle at which the light strikes the medium must be above the critical angle (which depends on refractive index)

50
Q

What is the relationship between refractive index and the critical angle?

A

The higher the refractive index the lower the critical angle

51
Q

How do you work out critical angle?

A 
Inverse Sin (1/n)
for air

or
Sin critical angle = refractive index of second medium / refractive index of incidence medium

Physics (9 decks)

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