4.4 - Waves

Question 1

What is a progressive wave

Answer 1

A wave which transfers energy from one point to another with a wave front that travels through the material

Question 2

What is a longitudinal wave

Answer 2

A wave which oscillates in the same direction as the energy (rarefactions and compressions)

Question 3

What is a transverse wave

Answer 3

A wave where the particles oscillate perpendicular to the energy (like EMF waves)

Question 4

What is frequency measured in

Answer 4

Hertz (Hz)

Question 5

What is wavelength

Answer 5

The distance between 2 adjacent points (e.g. peaks)

Question 6

How to find time period of a wave using frequency

Answer 6

T = 1 / f

Question 7

What is phase difference

Answer 7

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

Question 8

What do the axis on an oscilloscope measure

Answer 8

Vertical = Voltage / Amplitude
Horizontal = Time

Question 9

What is refraction

Answer 9

It is when a wave bends at a boundary between 2 materials due to the change in density causing it to speed up or slow down

Question 10

What is the difference between a polarised and unpolarised wave

Answer 10

Polarised waves contains waves oscillating along one axis. Unpolarised waves can be oscillating in any direction perpendicular to the axis of propagation

Question 11

How is intensity defined in terms of power

Answer 11

Intensity is power / area

Question 12

How fast do Electromagnetic waves travel in a vacuum

Answer 12

3x10^8 ms^-1 (speed of light)

Question 13

What is refractive index

Answer 13

The refractive index is a measure of how fast light travels in a material compared to its speed in a vacuum

Question 14

How to find refractive index of a material

Answer 14

n = c / v
n = refractive index
c = speed of light
v = velocity when in the material

Question 15

What is the name of the angle of incidence at which the light will reflect off a boundary rather than refracting in the medium

Answer 15

The critical angle

Question 16

How do you find the critical angle

Answer 16

SinC = 1 / n
C = critical angle
n = refractive index of material being passed into

Question 17

What is total internal reflection

Answer 17

What happens to light at angles greater than the critical angle

Question 18

What does it mean what a wave superposes

Answer 18

2 waves in the same place will combine to make a larger wave

Question 19

What is constructive interference

Answer 19

The waves superpose and produce a singular wave and the displacement of the wave is equal to the sum of the displacements (troughs and peaks go further in their respective directions)

Question 20

What is destructive interference

Answer 20

2 waves meet but the individual displacements are in opposite directions and counteract each other (Which could cause the wave to become a line)

Question 21

What experiment is used to investigate the principle of superposition using sound

Answer 21

2 speakers that emit the same signal are a moderate distance away from each other. Then walk along a line perpendicular to the speakers (along the wall opposite the speakers and should hear difference between loud and quiet points). This is because some points the waves interfere constructively and other points destructively.

Question 22

Will 2 waves in phase interfere constructively or destructively

Answer 22

Constructively

Question 23

What is path difference

Answer 23

It is the difference in distance that 2 waves have travelled in terms of wavelength (units of length)

Question 24

What is phase difference

Answer 24

The difference in the point in the cycle of 2 waves as a proportion of a full wave cycle (units of degrees/radians)

Question 25

Why is a laser used in showing intereference and diffraction

Answer 25

It produced monochromatic light (same wavelength/colour)

Question 26

What is Young's double-split experiment

Answer 26

A single source of light directed towards a double slit which creates 2 beams of light this interferes as it hits the screen and creates an interference pattern (dots being brighter and dimmer)

Question 27

What happens when you increase the slit width

Answer 27

It also increases the width of the central diffraction maximum

Question 28

What is the equation that relates the wavelength of light to the slit spacing and distance to the screen

Answer 28

λ = a x / D λ = wavelength a = slit spacing x = fringe spacing (on screen) D = distance to screen

Question 29

What are the 2 properties of light as a wave

Answer 29

Diffraction and Interference

Question 30

How to find number of fringes which would be produced by a diffraction grating

Answer 30

n λ = D sinθ

Question 31

What is the formula for total internal reflection

Answer 31

SinC = 1 / n

Question 32

What formula is used to determine the angle of refraction in to a new medium

Answer 32

n1sinθ1 = n2sinθ2 n1 = refractive index of previous material θ1 = angle it enters the material from n2 = new mediums refractive index θ2 = angle of refraction in the new material

Question 33

What is a stationary wave

Answer 33

They are waves that consist of alternating fixed pattern of nodes and antinodes. No energy is transferred across the wave just up and down

Question 34

What is a node

Answer 34

A point with no vibrations (amplitude is 0)

Question 35

What is an antinode

Answer 35

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

Question 36

What are the conditions for a stationary wave to be produced

Answer 36

The waves must be coherent The waves must be travelling in opposite direction. These conditions are met when a wave has reflected back onto itself

Question 37

Give an example of an experiment you could do to show a stationary wave

Answer 37

An oscillator is used to pass a wave along a sting which is fixed at one end and the wave will form when the progressive wave is reflected off the fixed end (Diff frequencies create different harmonics)

Question 38

What is a difference between a stationary and progressive wave

Answer 38

Stationary waves don't transmit energy from one place to another

Question 39

How to find speed of sound using resonance tube

Answer 39

Create a closed end pipe, using tuning fork hold above tube, move tube up until you find position which causes resonance, length will be a quarter of the wavelength, use speed = frequency x wavelength

Question 40

What is a harmonic

Answer 40

A harmonic is a point where the stationary wave form doesn't change because the waves in each direction are reinforcing each other

Question 41

A string is oscillating at its fundamental frequency (1st harmonic) how many nods and antinodes are visible

Answer 41

Nodes - 2 (one at either end) Antinode - 1 (in the middle) () this shape but sideways