Module 4 Basic Wave Properties / Refraction

Question 1

What is a progressive wave?

Answer 1

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

Question 2

What are the two types of progressive waves?

Answer 2

Longitudinal and transverse waves

Question 3

What is a longitudinal wave? Give an example

Answer 3

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

Question 4

What is a transverse wave? Give an example

Answer 4

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

Question 5

What waves can travel through a vacuum?

Answer 5

Electromagnetic waves

Question 6

What is displacement?

Answer 6

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)

Question 7

Amplitude

Answer 7

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

Question 8

What is wavelength?

Answer 8

Minimum distance between two adjacent points in phase

Question 9

Symbol for wavelength

Answer 9

λ, units in metres

Question 10

State 2 properties of sound waves

Answer 10

Longitudinal
and
Mechanical (need a medium to travel through)

Question 11

What is the time period of a wave?

Answer 11

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

Question 12

Symbol for time period

Answer 12

T - unit seconds

Question 13

What is the frequency of a wave?

Answer 13

The number of wavelengths per unit of time

Question 14

What are the crest and trough?

Answer 14

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

Question 15

What is rarefaction?

Answer 15

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

Question 16

What does the wave speed depend on?

Answer 16

the medium it is travelling through

Question 17

Derive the wave equation

Answer 17

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

Question 18

What does an oscilloscope show?

Answer 18

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

Question 19

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

Answer 19

volts

Question 20

What does CRO stand for?

Answer 20

cathode ray oscilloscope (usually just called an oscilloscope)

Question 21

How is amplitude displayed on an oscilloscope?

Answer 21

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

Question 22

How to get time period from oscilloscope

Answer 22

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

Question 23

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

Answer 23

reduces wave speed

Question 24

Suggest a method of observing reflection

Answer 24

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

Question 25

Definition of intensity

Answer 25

the radiant power passing through a surface per unit area

Question 26

What is the unit for intensity?

Answer 26

Wm^-2

Question 27

Equation for intensity?

Answer 27

I=P/A

Question 28

What properties does intensity have in reference to distance?

Answer 28

- 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

Question 29

What is the relationship between amplitude and intensity?

Answer 29

Intensity ∝ Amplitude^2

Question 30

Definition of refraction

Answer 30

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

Question 31

What is the refractive index?

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

no change in direction but the light changes speed

Question 34

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

Answer 34

greater the index the smaller the angle

Question 35

What effects are there when two refractive indices are equal?

Answer 35

ray of light continues along it's original pathway

Question 36

What stays the same during refraction?

Answer 36

frequency

Question 37

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

Answer 37

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

Question 38

How are wavelength and amount of refraction related?

Answer 38

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

Question 39

What is Snell's law?

Answer 39

nsin(θ)=constant

Question 40

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

Answer 40

- 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 air) to find refractive index for glass - then use sin(C) = 1/n to find critical angle C

Question 41

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

Answer 41

-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

Question 42

List wave phenomena for transverse waves

Answer 42

Reflection Refraction Interference Diffraction Polarisation

Question 43

List wave phenomena for longitudinal waves

Answer 43

Reflection Refraction Interference Diffraction

Question 44

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

Answer 44

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

Question 45

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

Answer 45

3/4 wavelength apart (270 degrees is 3/4 of 360)

Question 46

What is phase difference

Answer 46

the angle by which a wave lags or leads another sometimes used to compare two points on the same wave

Question 47

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

Answer 47

360 degrees or 2pi radians

Question 48

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

Answer 48

180 degrees or pi radians

Question 49

What is a compression on a longitudinal wave?

Answer 49

Region on a longitudinal wave where the particles are closest together (highest pressure)