A level Waves

Question 1

What is a progressive (moving) wave?

Answer 1

Something that carries energy from one place to another without transferring any matter

Question 2

What is the frequency of a wave?

Answer 2

1/period

Question 3

What is the wave equation that links the wave speed to the frequency and wavelength?

Answer 3

Wave Speed = Frequency x Wavelength

Question 4

What are transverse waves?

Answer 4

e.g electromagnetic waves
The vibrations (oscillations) are perpendicular to the direction of the wave

Question 5

What are longitudinal waves?

Answer 5

e.g sound waves
The direction of the vibrations(oscillations) is parallel to direction of the waves is travelling

Question 6

What does it mean for a wave to be reflected?

Answer 6

When a wave hits a boundary and bounces back

Question 7

What does it mean for a wave to be refracted?

Answer 7

The wave changes direction as it enters a different medium, due to it speeding up or slowing down.

Question 8

What is intensity?

Answer 8

A measure of how much energy a wave is carrying.
I= P/A

Question 9

What are the properties of EM waves?

Answer 9

They travel at 3x10^8 in a vacuum
They are all transverse
They can all be polarised (like all transverse waves)
Like all other progressive waves, they can carry energy

Question 10

What does it mean to polarise a wave?

Answer 10

Forcing a wave to oscillate only in a single plane of direction. It can only happen in transverse waves

Question 11

What is the relationship between polarization and reflection?

Answer 11

When light reflects it is partially polarised

Question 12

What effect does reflection have on the intensity of light?

Answer 12

At certain angles, light is partially polarised, causing a change in it’s intensity

Question 13

How can you use polarization to cause the intensity of a wave to be 0?

Answer 13

When there are two sources of polarization that are perpendicular to each other, the intensity is 0

Question 14

What is an interface?

Answer 14

The boundary between 2 different meida

Question 15

What happens to ultrasound waves when they hit an interface?

Answer 15

They are partially reflected and partially transmitted through the media

Question 16

What are ultrasound waves?

Answer 16

Waves that carry a frequency beyond the 20khz human hearing range

Question 17

What are ultrasound scans?

Answer 17

Short pulses of ultrasound radiation from images inside the body

Question 18

What process is used for ultrasound scans?

Answer 18

Ultrasound is directed into the body using a transducer

A gel is used to remove air pockets between air and skin and increase the penetrative effect on the ultrasound

When the ultrasound meets the interface inside your body (between different types of tissue) some of the ultrasound is reflected

A computer times how long it takes for the wave to return and uses that information to calculate the distance
Using the information it’s calculated the computer can generate an image

Question 19

How can you produce a clearer image from an ultrasound?

Answer 19

By having shorter pulses ( but not so short that they interfere with the transmission of the transducer)
Shorter wavelengths as they diffract less

Question 20

What is superposition?

Answer 20

When two or more waves pass through each other

Question 21

What is the principle of superposition?

Answer 21

When two or more waves pass over each other the resultant displacement is equal to the vector sum of the individual displacements

Question 22

What is constructive interference?

Answer 22

When two displacements (crest and a crest) or (trough and trough) superpose and add together to give a bigger displacement

Question 23

What is destructive interference?

Answer 23

When two or more displacements add together and cancel each other out.

Question 24

What does it mean for a wave to be in phase?

Answer 24

If two or more waves are both at the same point in their wave cycle. they always have the same displacement and velocity
When waves have a phase difference of 0 or a multiple of 360 or 2pi radians

Question 25

What does it mean for a wave to be in anti-phase?

Answer 25

Waves with odd multiples of 180 or pi radians

Question 26

What does it mean for waves to be coherent?

Answer 26

When the waves have the same wavelength and frequency and a fixed phase difference

Question 27

What is a key property of interference patterns?

Answer 27

The two sources must be coherent

Question 28

What is the path difference?

Answer 28

The amount by which the path of one wave is longer than the path of another wave

Question 29

What are the main properties of path difference?

Answer 29

At any point that is an equal distance from both sources, there will be constructive interference.
At any point where the path difference is a multiple of a whole number of wavelengths there will be constructive interference
At any point where the path difference is an odd multiple of a half wavelength you will get destructive interference due to the waves arriving out of phase

Question 30

What causes constructive interference to occur? (formula relating it to path difference)

Answer 30

path difference = nλ

Question 31

What causes destructive interference to occur? (formula relating it to path difference)

Answer 31

path difference = (2n+1)λ / 2

Question 32

What is a standing wave?

Answer 32

The superposition of two progressive waves with the same wavelength in the opposite direction.
They transmit no energy

Question 33

What are nodes?

Answer 33

Where the amplitude is 0

Question 34

What are antinodes?

Answer 34

Points of maximum amplitude

Question 35

What is the first harmonic?

Answer 35

1/2(wavelength) of a wave

Question 36

How can you investigate the factors affecting the resonant frequencies?

Answer 36

Measure the mass length of the string
Use this to find the mass per unit length ( m/L)
Set up an apparatus using:
signal generator, vibration transducer, string, and pulley
Measure the tension using (T = Weight)
Turn on the signal generator and very the frequency until you find the first harmonic
Keep the string type and the tension in the string the same and alter the length. Do this by moving the transducer and then find the first harmonic again.

Question 37

What are the properties of the resonant frequency?

Answer 37

The longer the string, the lower the resonant frequency
The heavier the string, the lower the resonant frequency
The looser the string the lower the resonant frequency

Question 38

What is diffraction?

Answer 38

The way that waves spread out as they come through a narrow gap or round obstacles

Question 39

What factor affects diffraction?

Answer 39

The size of the gap and the wavelength of the wave

Question 40

What happens if the gap is large in comparison to the wavelength?

Answer 40

There would be very little diffraction

Question 41

What happens if the gap is the same size as the wavelength?

Answer 41

The most difration

Question 42

What happens if the gap is smaller than the wavelength?

Answer 42

The wave can no longer pass through or get reflected

Question 43

What is Huygens’ construct?

Answer 43

The use of circles to predict how refraction will occur

Question 44

What are sound waves

Answer 44

Longitudinal waves that oscillations are parallel to direction and has a series of rarefrations and compression

Question 45

What are white light waves?

Answer 45

Summation of many waves of different frequency

Question 46

How can diffraction cause changes in colours?

Answer 46

Diffraction causes waves to spread out, causes interpherence—> interpherence —> amplification and cancellation of certain wave lengths

Question 47

What’s a diffraction grating?

Answer 47

A slide containing many equally spaced slits very close together.

Question 48

The formula relating change in wavelength to the change in velocity of a wave?

Answer 48

v/c =Δλ/λ

Question 49

Diffraction grating formula?

Answer 49

dsinθ = nλ