Wave behaviour

Question 1

Superposition

Answer 1

When two or more waves overlap (superpose), the resultant displacement is the sum of the individual displacements.
This is often called interference

Question 2

Wavelength (m)

Answer 2

The distance between any two points at the same part of the wave

Question 3

Amplitude

Answer 3

Maximum displacement of a wave from the equilibrium position

Question 4

Time period (s)

Answer 4

Time for one wavelength to pass a particular point

1/f

Question 5

Frequency (Hz)

Answer 5

Number of wavelengths passing a particular point per second

1/T

Question 6

Phase

Answer 6

Stage in a wave cycle

If waves are at the same stage they are in phase, if not they are out of phase

Question 7

Phasor

Answer 7

A rotating arrow that can be used to represent different phases by an angle between 0-2π

Question 8

Phase difference

Answer 8

Difference in the stages of different waves and can be measured by their individual phase angle
The phase difference between in phase and in antiphase is π

Question 9

Displacement formula

Answer 9

displacement = a.sin(θ)
= a.sin (2πft)

a = radius of phasor
θ = phase angle

Question 10

Formation of standing waves

Answer 10

Waves move down a tube or along a string etc
They reflect at one end
The reflected waves superpose with the original waves
This interference leads to the formation of nodes and antinodes

λ = 2L/N

N = 2L/λ

L = Nλ/2

Question 11

Node

Answer 11

Point of zero (minimum) displacement

Question 12

Antinode

Answer 12

Point of maximum displacement

Question 13

Wave speed equation

Answer 13

v = f.λ

Question 14

Refractive Index and Snell’s Law

Answer 14

RI = (c in medium 1) / (c in medium 2)
= sin (i) / sin (r) [this is Snell’s Law]

where the angle of incidence (i) is the angle between the normal and the incident beam
and the angle of refraction (r) is the angle between the normal and the refracted beam

Question 15

Absolute refractive index (of a material)

Answer 15

The ratio when medium 1 is a vacuum, and the second medium is the material

Question 16

Huygens and wavelets

Answer 16

Early explanation of waves and wave behaviour

Imagined waves as being made up of smaller wavelets that spread out and interfered with each other from each wavefront
However, due to parts of each wavelet being in phase and in they all superpose and cancel apart from consistent wavefronts in the direction the wave is travelling

Question 17

Path difference

Answer 17

The difference in the distance that different waves have travelled to reach a particular point
If the difference is an integer multiple of λ then the waves will meet in phase
If the difference is an (integer + 0.5) multiple of λ then the waves will meet in antiphase

Question 18

Coherence

Answer 18

Waves are coherent if they have a constant phase difference, otherwise they are incoherent

Question 19

Constructive interference

Answer 19

Where waves interfere to create a larger superposition amplitude

Question 20

Diffraction

Answer 20

When a wave passes through a gap roughly the same width as their wavelength, the waves spread out
The smaller the gap relative to the wavelength, the more it spreads out

Question 21

Young’s double split experiment

Answer 21

Passing light through two narrow slits very close together leads to a diffraction pattern forming on a screen behind the slits
At minimas the waves reach the screen in antiphase and destructively interfere leading to no light on the screen
At maximas the waves reach in phase, constructively interfere and it leads to bright spots
The path difference between maximas and minimas is π
Brightest slit at n=0 because of largest resultant vector

Question 22

Double slit equation

Answer 22

nλ = dsinθ
= d(x/L)

d = space between slits

Question 23

Diffraction grating separation

Answer 23

line separation (m or mm) = 1/lines per m or mm

Question 24

Single slit defraction

Answer 24

nλ = bsinθ

b = width of slit