Topic 5 - Waves Pt1

Question 1

What do waves do?

Answer 1

• a progressive (moving) wave carries energy from one place to another without transferring any material
• the transfer of energy is in the same direction as the wave is travelling
• as waves carry energy the source of the wave loses energy

Question 2

What’s the displacement of a wave?

Answer 2

(Meters)

How far a point in the wave has moved from its undisturbed position

Question 3

What’s the amplitude of a wave?

Answer 3

Meters

The maximum magnitude of the displacement

Question 4

What’s the wavelength of a wave?

Answer 4

Meters

The length of one whole wave cycle (from crest to crest or trough to trough)

Question 5

What’s the period of a wave?

Answer 5

Seconds

The time taken for a whole cycle (vibration) to complete

Question 6

What’s the frequency of a wave?

Answer 6

Hertz

The number of cycles per second passing a given point

Question 7

What’s the phase of a wave?

Answer 7

A measurement of the position of a certain point along the wave cycle

Question 8

What’s the phase difference of a wave?

Answer 8

The amount one wave lags behind another

Question 9

How would you find frequency?

Answer 9

Frequency = 1 / period
f = 1 / T
1 Hz = 1s*-1

Question 10

How would you calculate wave speed?

Answer 10

Speed of wave (v) = frequency (f) x wavelength

Question 11

What’s a longitudinal wave?

Answer 11

• it consists of alternate compressions & rarefactions of the medium it’s travelling through
• compressions & rarefactions create pressure variations
• at point of compression, molecules are closer together, increasing pressure at that point
• at point of rarefaction, molecules are further apart, which means a lower pressure at that point

Question 12

What’s an example of a longitudinal wave?

Answer 12

A sound wave

Question 13

What are transverse waves?

Answer 13

The vibrate perpendicular to the direction of energy transfer

Question 14

What are 2 examples of a transverse wave?

Answer 14

• all electromagnetic waves

- water waves

Question 15

What 2 waves can you draw a transverse wave?

Answer 15

• on displacement (y) against distance along the path of the wave (x) where you can read the wavelength from the x axis
• displacement (y) against time (x) you can measure 1 period from the x axis

Question 16

What happens when a wave is reflected?

Answer 16

-the wave is bounced back when it hits a boundary

Question 17

What happens when a wave is refracted?

Answer 17

• the wave changes direction as it enters a different medium
• the change in direction is a result of a wave slowing Down or speeding up

Question 18

Define intensity?

Answer 18

The rate of flow of energy per unit area at right angles to the direction of travel of the wave
Units: W m*-2

Question 19

What’s the equation for intensity?

Answer 19

Intensity = power / area

Question 20

What properties do em waves have in common?

Answer 20

• travel in a vacuum at the speed of 3 x 108 ms-1
• they’re transverse consisting of vibrating electric and magnetic fields which are at right angles to each other and to the direction of travel
• they can refracted, reflected and diffracted and can undergo interference
• they carry energy
• they can be polarised

Question 21

What is the plane of polarisation?

Answer 21

-the plane in which a wave vibrates

Eg. A rope would be polarised in the vertical plane by the fence

Question 22

What’s plane polarisation?

Answer 22

It’s polarising a wave so it only oscillates in 1 direction

Question 23

How can you prove that light is transverse?

Answer 23

By polarising it as polarisation can only happen for transverse waves

Question 24

What happens when the transmission axes of 2 polarising filters are aligned?

Answer 24

All the light that passes through the first filter also passes through the second

Question 25

What happens when the transmission axes of 2 polarising filters are not aligned, and the second filter is rotated?

Answer 25

- the amount of light that passes through the second filter varies - as it’s rotated less light will be able to get through - the intensity of the light getting through the second filter will gradually decrease

Question 26

What happens when the transmission axes of 2 polarising filters at 45 degrees to each other?

Answer 26

The intensity will be half that getting through the first filter

Question 27

What happens when the transmission axes of 2 polarising filters are at right angles to each other?

Answer 27

No light will pass through - intensity is 0 (If you continue to turn it the intensity will begin to increase again, when the two axis realign after a 180 degree rotation, all the light will be able to pass through the second filter)

Question 28

Explain what would happen if you direct a beam of unpolarised light at a reflective surface then view the reflected Ray through a polarising filter?

Answer 28

- the intensity of light leaving the filter changes with the orientation of the filter - the intensity changes because at certain angles light is partially polarised when it’s reflected - (this is used to remove unwanted reflections in photography & in Polaroid glasses to remove glare)

Question 29

Explain why metal grilles are used to polarise microwaves?

Answer 29

- because polarising filters don’t work on them as there wavelength is too long - instead metal grilles are used - intensity drops to 0 when the plane of polarisation of the metal grille is at right angles to the plane of polarisation of the microwaves, because the grille is absorbing their energy