Waves

Question 1

Reflection

Answer 1

Wave changes direction at the boundary of a medium:

• moves away from new medium
• angle of incidence = angle of reflection

Question 2

Refraction

Answer 2

Wave changes direction as it passes between mediums:

• moves into new medium
• wavelength and speed change
• wave bends towards normal when slowing down

Question 3

Find wave speed

Answer 3

Speed = wavelength*frequency
(v = λf)

Question 4

Polarised waves

Answer 4

• oscillations in only one plane

- only transverse waves

Question 5

Polarising filter

Answer 5

• filters oscillations into one direction
• unpolarised&raquo_space; polarised causes a brightness decrease
• polarised&raquo_space; polarised effect depends on angle of the filters

Question 6

Result of two parallel polarising filters

Answer 6

Same as a single filter

Question 7

Result of two perpendicular polarising filters

Answer 7

Blocks most light

Question 8

Intensity

Answer 8

Radiant power through a surface per unit area

P/A

Question 9

Find intensity at distance r from a spherical wave source

Answer 9

Intensity = power/spherical surface area
(I = P/4πr²)

Question 10

Relationship between intensity and amplitude

Answer 10

Intensity is proportional to amplitude^2

Question 11

Snell’s law

Answer 11

n1sin(i) = n2sin(r)

Question 12

Find refractive index

Answer 12

Refractive index = speed in vacuum/speed in material

n = c/v

Question 13

Where are angles measured from in reflection and refraction?

Answer 13

The normal to the boundary

Question 14

Snell’s law for critical angle

Answer 14

n1*sin(i) = n2

because angle of refraction is 90 so sin(r) = 1

Question 15

Total internal reflection

Answer 15

When angle of incidence is greater than the critical angle, so only reflection happens

Question 16

Coherent waves

Answer 16

Waves with a constant phase difference at their sources

Question 17

Wave superposition

Answer 17

Two waves overlap and resultant displacement = sum of individual displacements

Question 18

How to form a stationary wave

Answer 18

Interference of two progressive waves with:

• opposite directions
• same speed
• same frequency

Question 19

Nodes of a stationary wave

Answer 19

Points with no amplitude (displacement always 0)

Question 20

Antinodes of a stationary wave

Answer 20

Points with max amplitude

Question 21

Find wavelength using a diffraction pattern

Answer 21

Wavelength = slit separation*fringe separation/distance from screen
(nλ = dsinθ
or
nλ = ax/D)

Question 22

Find wave period

Answer 22

Period = 1/frequency
(T = 1/f)

Question 23

Find frequency (using wavelength)

Answer 23

Frequency = speed/wavelength
(f = v/λ)

Question 24

Find frequency (using period)

Answer 24

Frequency = 1/period
(f = 1/T)

Question 25

Transverse wave

Answer 25

Wave where oscillations are perpendicular to wave direction

Question 26

Longitudinal wave

Answer 26

Wave where oscillations are parallel to wave direction

Question 27

When is diffraction through a gap strongest?

Answer 27

When gap width = wavelength

Question 28

Wavelength range of radio

Answer 28

> 0.1 m

Question 29

Wavelength range of microwaves

Answer 29

1 mm < λ < 0.1 m

Question 30

Wavelength range of infrared

Answer 30

700 nm < λ < 1 mm

Question 31

Wavelength range of light

Answer 31

400 nm < λ < 700 nm

Question 32

Wavelength range of ultraviolet

Answer 32

10 nm < λ < 400 nm

Question 33

Wavelength range of x-rays and gamma rays

Answer 33

< 10 nm

Question 34

Properties of EM radiation

Answer 34

- can be reflected, refracted and diffracted - transverse (so can be polarised) - can travel through a vacuum (at 3 x10^8 m/s)

Question 35

1st order maxima

Answer 35

The set of points in an interference pattern where: - path difference = 1 λ - phase difference = 2π (same as 0) - there is constructive interference - resultant wave with max amplitude is formed

Question 36

1st order minima

Answer 36

The set of points in an interference pattern where: - path difference = 0.5 λ - phase difference = π - there is destructive interference - resultant wave with min amplitude is formed

Question 37

Phase difference

Answer 37

Difference in wave cycle progress between two points on a wave / waves (written as the diff in x value of two sin graphs)

Question 38

Path difference

Answer 38

Difference in the distances of two waves from their own sources (can be measured in regular distance or in wavelengths)

Question 39

Constructive interference

Answer 39

Superposition of two coherent waves in phase to form a resultant wave of maximum amplitude

Question 40

Destructive interference

Answer 40

Superposition of two coherent waves in antiphase to form a resultant wave of minimum (or 0) amplitude

Question 41

Amplitude

Answer 41

A wave's maximum displacement from equilibrium

Question 42

Wave displacement

Answer 42

Distance of a point from equilibrium in a given direction

Question 43

Wavelength

Answer 43

Distance between adjacent peaks of a wave

Question 44

Wave period

Answer 44

Time taken for one wavelength to pass a point | or time taken for a full oscillation at one point

Question 45

Frequency

Answer 45

Number of wavelengths that pass a point per second | or number of full oscillations per second at one point

Question 46

Interference

Answer 46

Superposition of coherent waves

Question 47

Points in phase with each other in progressive vs standing waves

Answer 47

Progressive - points that are one wavelength apart are in phase Standing - all points on the same side of equilibrium are in phase (same wave cycle progress)

Question 48

Energy transfer in progressive vs standing waves

Answer 48

Progressive - energy transferred in wave direction | Standing - no net energy transfer

Question 49

Amplitude in progressive vs standing waves

Answer 49

Progressive - all points have the same amplitude | Standing - amplitude changes along the wave (max at antinodes and 0 at nodes)

Question 50

Fundamental frequency of a taut string / open tube

Answer 50

- frequency of the first standing wave that the string / tube can form (first harmonic) - both ends are nodes for a string - both ends are antinodes in a tube - wavelength is double the string / tube length

Question 51

Harmonics

Answer 51

Standing waves used to make sound in an instrument - frequency is a multiple of the fundamental frequency (odd multiples for closed tubes)

Question 52

Fundamental frequency of a closed tube

Answer 52

- frequency of the first standing wave that the tube can form - open end must be an antinode - closed end must be a node - wavelength is 4x the tube length

Question 53

Wavelength in standing waves

Answer 53

Double the distance between two adjacent nodes