Waves

Question 1

Amplitude

Answer 1

Maximum displacement from the equilibrium.

Question 2

Frequency

Answer 2

The number of complete oscillations passing through a point per second.

Question 3

Wavelength

Answer 3

The length of one whole oscillation (e.g. the distance between successive
peaks/troughs).

Question 4

Phase

Answer 4

The position of a certain point on a wave cycle, (units are radians, degrees or
fractions of a cycle).

Question 5

Phase
difference

Answer 5

How much a particle/wave lags behind another particle/wave, (units are
radians, degrees or fractions of a cycle).

Question 6

Period

Answer 6

Time taken for one full oscillation.

Question 7

What is a progressive wave?

Answer 7

A wave made up of oscillating particles, transfers energy without transferring materials.

Question 8

In phase

Answer 8

Whole number of wavelengths, e.g. nλ

Question 9

Out of phase

Answer 9

Whole number + a half wavelengths (n+1/2)λ

Question 10

What is the difference between longitudinal and transverse waves?

Answer 10

Transverse waves have oscillations perpendicular to the direction of energy transfer, while longitudinal waves have oscillations parallel to the direction of energy transfer.

Question 11

What is a polarised wave?

Answer 11

A wave that oscillates in only one plane (only transverse waves can be polarised as polarisation can only occur if a wave’s oscillations are perpendicular to the direction of energy transfer).

Question 12

What are the applications of polarisation?

Answer 12

Polaroid sunglasses, TV and radio signals.

Question 13

What is superposition?

Answer 13

Displacements combined as they pass.

Question 14

What is a stationary/standing wave?

Answer 14

Superposition of 2 progressive waves travelling in opposite directions in the same plane. Same wavelength, amplitude and frequency. No energy is transferred.

Question 15

What are nodes?

Answer 15

Areas of no displacement, where the waves meet out of phase and destructive interference occurs.

Question 16

What are anti-nodes?

Answer 16

Areas of maximum displacement, where waves arrive in phase, and constructive interference occurs.

Question 17

What is the first harmonic?

Answer 17

Lowest frequency at which a stationary wave forms.

Question 18

How do you find the frequency of higher harmonics?

Answer 18

Frequency of the first harmonic multiplied by the harmonic number. (e.g. f, 2f, 3f…)

Question 19

What is the path difference?

Answer 19

Difference in distance travelled by 2 waves.

Question 20

Coherent

Answer 20

Same frequency, wavelength, and a fixed phase difference.

Question 21

Monochromatic

Answer 21

Emits light of a single wavelength.

Question 22

Why must the slits be the same size as the wavelength of the light in Young’s double slit experiment?

Answer 22

Light diffracts the most. When the gap is smaller, most waves are reflected, and when the gap is larger, there is less noticeable diffraction.

Question 23

Why is a single slit places before the double slit in Young’s double slit experiment?

Answer 23

Light must be coherent. By placing the single slit before, the light has a fixed path difference.

Question 24

What can we use to make light monochromatic?

Answer 24

A filter.

Question 25

What precautions must we take when using lasers?

Answer 25

Display a warning sign, wear laser safety goggles, do not shine the laser at anyone or at any reflective surfaces.

Question 26

What pattern is seen in Young's double slit experiment?

Answer 26

A pattern of alternating light and dark fringes.

Question 27

What happens when sound waves interfere?

Answer 27

Rhythmic change in amplitude, loud to soft. The frequency of the new wave is the difference between the original two waves.

Question 28

Which waves diffract more?

Answer 28

Waves with longer wavelengths and lower frequencies. Waves with shorter wavelengths and higher frequencies diffract less.

Question 29

Stationary waves in an open tube

Answer 29

Node at the bottom, anti-node at the top.

Question 30

What is diffraction?

Answer 30

The spreading out of waves when they pass through or around a gap.

Question 31

What is the single slit diffraction pattern for monochromatic light?

Answer 31

Bright central fringe with alternating light and dark fringes either side (smaller).

Question 32

What is the single slit diffraction pattern for white light?

Answer 32

The different wavelengths of light are diffracted by different amounts - spectrum of colour. White central maximum, either side spectrum of colours, violet closest, red furthest.

Question 33

What happens when the slit width increases?

Answer 33

Diffraction decreases, central maximum becomes narrower and intensity increases.

Question 34

What happens when the wavelength increases?

Answer 34

Diffraction increases, central maximum becomes wider and intensity decreases.

Question 35

What is a diffraction grating?

Answer 35

A slide containing equally spaced slits very close together.

Question 36

What happens when monochromatic light is passed through a diffraction grating?

Answer 36

When monochromatic light is passed through, the pattern is sharper and brighter.

Question 37

The more slits there are...

Answer 37

...the more the pattern is reinforced, it is therefore sharper and brighter.

Question 38

What is the refractive index?

Answer 38

Measures how much a material slows down light passing through it.

Question 39

What happens when the angle of refraction = 90 degrees?

Answer 39

The light is refracted along the boundary. At this point, the angle of incidence is the critical angle.

Question 40

When does total internal reflection occur?

Answer 40

When the angle of incidence is greater than the critical angle, therefore the refracted ray is reflected back, angle of refraction > 90 degrees. Material 1's refractive index must be greater than material 2's refractive index.

Question 41

Application of TIR: Optic fibres

Answer 41

Optic fibres are thin, flexible tubes of plastic or glass that carry information in the form of light signals. It has an optically dense core (high refractive index) surrounded by cladding with a lower optical density (lower refractive index) so TIR can occur. Cladding protects the core from damage and prevents signal degradation.

Question 42

What is signal degradation?

Answer 42

Losing information in the form of signals.