Topic 4.4: Waves

Question 1

progressive wave

Answer 1

a wave which transfers energy from one place to another with a wave front which travels through a material

Question 2

longitudinal wave

Answer 2

a wave which oscillate in the same direction as energy propagation
there are rarefactions and compressions

Question 3

transverse wave

Answer 3

a wave where the particle oscillations are perpendicular to the energy propagation

Question 4

what is frequency ?

Answer 4

the number of waves passing through a point per second
measured in Hertz

Question 5

wavelength

Answer 5

the distance between two adjacent corresponding points on a wave

Question 6

amplitude

Answer 6

the maximum displacement of the wave from its equilibrium position

Question 7

what is the phase difference ?

Answer 7

the amount one wave lags behind another as a proportion of the wavelength
measured in radians or degrees

Question 8

refraction

Answer 8

is when a wave bends at a boundary between two materials due to the difference in density causing it to speed up or slow down

Question 9

what is the difference between polarised and unpolarised waves ?

Answer 9

polarised waves only contains waves oscillating on one axis
unpolarised waves can be oscillating in any direction perpendicular to the axis propagation

Question 10

describe how a ripple tank may be used to investigate diffraction

Answer 10

create water waves in the tank
vary the size of a gap for them to pass through
note how the direction of the waves passing through changes

Question 11

How is intensity defined in terms of power ?

Answer 11

intensity is power/area

Question 12

how are intensity and amplitude related

Answer 12

intensity is proportional the amplitude squared

Question 13

what is the refractive index of a material ?

Answer 13

it is a measure of how fast light travels in a material compared to its speed in a vacuum

n = c/v speed of light / velocity in material

Question 14

what is superposition ?

Question 15

what are coherent waves ?

Answer 15

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

Question 16

what is path difference ?

Answer 16

path difference is the difference that two waves have travelled in terms of wavelength

Question 17

what is phase difference ?

Answer 17

phase difference is the difference in the point in the cycle of two waves as a proportion of a full wave cycle

Question 18

why is a laser useful in showing interference and diffraction ?

Answer 18

it produces monochromatic (same wavelength/colour)

Question 19

what is Youngs double slit experiment ?

Answer 19

a single source of light directed towards a double slit , which creates two coherent beams of light.
this interferes as it hits the screen and creates an interference pattern

Question 20

what two properties can only be explained if it is a wave ?

Answer 20

diffraction
inteference

Question 21

what is a stationary wave ?

Answer 21

stationary waves consists of alternating fixed pattern of nodes (points with zero amplitude) and antinodes (points with maximum amplitude)
no energy is transferred across the wave

Question 22

what is a node ?

Answer 22

a point with no vibrations in which the resultant amplitude is 0

Question 23

what is an antinode ?

Answer 23

a point with maximum vibration in which the resultant amplitude is at maximum

Question 24

what are the conditions for a stationary wave to be produced ?

Answer 24

the waves must be coherent
they must be travelling in opposite directions

Question 25

how could you use the formation of stationary waves in a resonance tube to find the speed of sound ?

Answer 25

create a closed end pipe using a hollow pipe inside a measuring cylinder containing water
using a tuning fork (producing a known frequency) and hold above tube
move the tube up until you find the first position which causes resonance
this length would be a quarter of the wavelength
use speed = frequency * wavelength

Question 26

what is meant by harmonics ?

Answer 26

harmonics are points where the stationary wave form doesn’t change because the waves in each direction are reinforcing each other

Question 27

how a stationary wave is formed on a string ?

Answer 27

• the wave reflected superposes with the incident wave
  to produce a resultant wave with nodes and antinodes

Question 28

what is interference ?

Answer 28

when two or more waves superpose at a point and there is a change in overall displacement

Question 29

what is a plane polarised wave ?

Answer 29

oscillations are in one direction only
perpendicular to the direction of energy transfer