Waves

Question 1

Continuous Wave definition

Answer 1

Constant amplitude and frequency

Question 2

Wavelength definition

Answer 2

The distance between any point and the next identical point

Question 3

Frequency definition

Answer 3

Number of oscillations in one second

Measured in Hz

Question 4

Frequency and Time equation

Answer 4

f = 1/T

Question 5

Speed/Frequency/Wavelength equation

Answer 5

c = f * wavelength
m/s = Hz * m

Question 6

Dispersion definition

Answer 6

Waves separate out whilst travelling through a medium

Due to different wavelengths travelling at different speeds

Question 7

Displacement definition

Answer 7

Distance from the centre of the oscillation to the particle

Vector, so can be negative

Question 8

Amplitude definition

Answer 8

Maximum displacement

Question 9

Energy/Amplitude equation

Answer 9

Energy is directly proportional to amplitude squared

E = k A^2

Question 10

Out of phase definition

Answer 10

Two waves with same frequency and wavelength, but one is shifted compared to the other

Question 11

Single slit diffraction pattern

Answer 11

Central maxima

Decreasing height of maxima as you get further from centre

Question 12

Double slit interference

How to increase fringe separation

Answer 12

Distance from slits to screen is increased
Wavelength of light used is increased
Slit spacing (distance between centres of slits) is decreased

Question 13

Fringe separation equation

Answer 13

w = λD/s
w = fringe separation
λ = wavelength of light
D = distance from slits to screen
s = slit spacing

Question 14

Slit spacing definition

Answer 14

Distance between centres of slits

Question 15

Why are fringes formed

Answer 15

Interference of light

Question 16

Why are bright fringes formed from double slit

Answer 16

Light waves from each slit are in phase

Path difference = lambda

Question 17

Why are dark fringes formed from double slit

Answer 17

Light waves from each slit arrive 180º out of phase

path difference = lambda/2

Question 18

Why are lasers used in double slit experiments

Answer 18

Coherent source of light => no need for a single slit before.
Photons in a laser beam are in phase with each other

Highly monochromatic, meaning its wavelength can be calculated to within a nanometre

Question 19

What happens when white light is used for double slits

Answer 19

Central fringe is white
Each component colour of white light produces its own fringe pattern
Each pattern is centred on the screen at the same position

Question 20

Principle of superstition

Answer 20

Exact moment when 2 waves meet
Crest + crest = super crest
Trough + trough = super trough
Crest + trough = 0 displacement
- If waves aren't of equal magnitude, crest + trough = minimum

Question 21

In phase definition

Answer 21

Two waves superimpose constructively

Question 22

Anti phase definition

Answer 22

two waves superpose destructively

Question 23

Node definition

Answer 23

Resultant wave = 0 displacement

No oscillation

Question 24

Anti-node definition

Answer 24

Resultant waves has largest amplitude

Maximum oscillation

Question 25

Distance between nodes

Answer 25

= distance between antinodes

= wavelength/2

Question 26

Difference between transverse and longitudinal waves

Answer 26

Transverse:
vibrations act perpendicular to direction of energy transfer

Longitudinal:
vibrations occur parallel to direction of energy transfer

Question 27

How is light proven as a wave?

Answer 27

Interference
- Used if the size of the object is comparable to the wavelength of the light

Or diffraction and polarisation

Question 28

How is light proven as a particle?

Answer 28

Photo-electric effect

- Used if the energy is comparable to the energy of the photon (E=hf)

Question 29

Which experiment(s) prove light could be both a wave and a particle?

Answer 29

Reflection

Refraction

Question 30

Emission vs absorption

Answer 30

1. Hot object will emit a continuous spectrum of light
2. Cool gas will absorb some of the photons with specific energies, exciting the orbital electrons
3. Orbital electrons will return to the ground state and emit photons with the same frequency

Question 31

Forced vibrations definition

Answer 31

Vibrations/oscillations of a system subjected to an external periodic force

Question 32

Resonance definition

Answer 32

System vibrates such that its velocity is in phase with the periodic force
An oscillating body that is not resonating will return to its natural frequency when the forcing vibration is removed

Question 33

Damped oscillations definition

Answer 33

Oscillations that reduce the amplitude for ALL frequencies due to the presence of resistive forces such as friction and drag

1. Lightly dampened system, amplitude of oscillations decreases gradually
2. Heavily dampened system displaced from equilibrium then released, the system slowly returns to equilibrium without oscillating
3. Critically damped system, it returns to equilibrium in the least possible time without oscillating

Question 34

As an applied frequency to a system increases…

Answer 34

1. The amplitude of oscillations increases until it reaches a maximum amplitude at a particular frequency, and then the amplitude decreases again
2. Phase difference between DISPLACEMENT AND THE PERIODIC FORCE increases from 0 to pi/2 at maximum amplitude, then from pi/2 to pi as the frequency increases further

Question 35

Resonant frequency definition

Answer 35

The frequency of a system at the maximum amplitude

Question 36

For an oscillating system with little/no dampening, at resonance…

Answer 36

The applied frequency of the periodic force = the natural frequency of the system

Question 37

Diffraction grating definition

Answer 37

A plate with may closely ruled parallel slits on it

Question 38

How is the angle of diffraction between each transmitted beam and the central beam increased (diffraction grating)

Answer 38

Light with longer wavelength used (e.g. blue filter instead of red filter)
Grating with finer slits is used

Question 39

Diffraction grating equation

Answer 39

d * sin theta = n * lambda

d = slit separation (number of slits/metre = 1/d)
theta = angle between central maxima and nth order
n = order number
lambda = wavelength of light used

Question 40

What does an increase of the number of slits do (diffraction grating)

Answer 40

Narrower peaks
More precise measurements
Increased intensity
Higher concentration of light

Question 41

Electromagnetic spectrum

Answer 41

Smallest frequency => highest frequency
Largest wavelength => shortest wavelength
Radio waves - microwaves - Infared - visible - UV - X-Ray - Gamma Ray

Visible light:
Violet shortest wavelength, red longest
BLUE HAS SHORTER WAVELENGTH THAN RED

Question 42

Types of spectra

Answer 42

Continuous
Shows all colours
Most intensive part of the spectrum depends on temperature
- Hotter the light source, the shorter the wavelength of most intensive part
Means that by measuring the wavelength of most intensive part, we can measure the temperature of the light source

Line emission
Glowing gas in a vapour lamp/discharge tube emits light at specific wavelengths
Characterised by the chemical element that produced the light

Line absorption
Continuous spectrum with narrow dark lines at certain wavelengths
Due to elements in glowing gas, which absorb light of the wavelengths they can emit, so the transmitted light is missing these wavelengths

Question 43

Young’s double slit

How is the pattern formed on the screen?

Answer 43

Each slit diffracts light, emitting waves
Two slits act as coherent sources of light
Proves light is a wave as interference is a wave property
Bright fringes formed when light from one slit reinforces light from the other
Light from slits is in phase at a maxima, causing reinforcement
Path difference to bright fringe = n lambda (whole number of wavelengths)
Path difference to a dark fringe = (n+1/2) lambda (half wavelengths)