Chapter 5 - Waves [Complete]

Question 1

What is a progressive wave?

Answer 1

A wave that transfers through a substance or space, transferring energy and information

Question 2

What is the amplitude of a wave?

Answer 2

The maximum perpendicular displacement from the particle’s undisturbed position. The larger the amplitude, the larger the energy transferred

Question 3

What is the wavelength of a wave?

Answer 3

The distance between wave peaks or two equivalent points on two successive cycles

Question 4

What is the frequency of a wave and what is its unit?

Answer 4

The amount of cycles or vibrations of the wave per second, measured in Hertz (Hz)

Question 5

What is the equation linking time period and frequency?

Answer 5

f = 1/T

Question 6

What does it mean if two particles moving along a wave are in phase?

Answer 6

They are moving in the same direction at the same speed

Question 7

What does it mean if two particles are moving in antiphase?

Answer 7

They are moving with the same speed, but in the exact opposite perpendicular directions. Particles moving in anti phase are separated by a distance of a whole number n of wavelengths + an extra half wavelength

Question 8

How do you calculate an abstract phase difference? (aka one that is not exactly half a wavelength or a full wavelength etc.)

Answer 8

Find the difference in distance between the two points, and then times it by 2Pi radians and divide it by the wavelength

Question 9

What is the equation to find the vertical displacement of a particle in a wave at any point of its cycle, given that the wave is sinusoidal?

Answer 9

V. displacement = Amplitude x sin([2 x Pi x t] / Time period)

Question 10

What happens to a wave’s phase when it is reflected off a surface?

Answer 10

It undergoes a phase change of 180 degrees

Question 11

What is a longitudinal wave?

Answer 11

A wave where the particles vibrate parallel to the direction the energy is travelling in

Question 12

What is a transverse wave?

Answer 12

A wave where the vibrations are at right angles to the direction the energy is travelling in

Question 13

What are electromagnetic waves?

Answer 13

A transverse waves that travel at the speed of light (3 x 10^8), they are made up of two component waves - one that is oscillating within the electric field, and the other in the magnetic field

Question 14

What is a mechanical wave?

Answer 14

A wave that needs a medium to pass through, and thus cannot travel in a vacuum

Question 15

Through which state does sound travel quickest?

Answer 15

Solids, 5100 m/s

Question 16

What 3 wave groups have wavelengths shorter than that of visible light (10^-6)m?

Answer 16

Gamma rays, X-rays, UV

Question 17

What effect does radio waves have on the body?

Answer 17

Minimal to negligible

Question 18

What is the threat of X-rays, gamma rays, and UV light?

Answer 18

They can be ionising to cells/increase the risk of cancer

Question 19

What are radio waves used for commercially?

Answer 19

To transmit radio and TV through carrier waves or through radio telescopes that can receive and interpret radio waves from space

Question 20

Why is normal light unpolarised?

Answer 20

As the excited electrons that cause the emission of the light can vibrate in any direction, and thus the electric and magnetic fields of light can oscillate in any direction

Question 21

Which type of wave can be polarised?

Answer 21

Transverse waves, and only transverse waves

Question 22

What is it called when two polarising filters are held at right angles to one another and no light gets through?

Answer 22

Crossing the polarisers

Question 23

Other than through polarising filters, how else can light sometimes be polarised?

Answer 23

Through reflection off some surfaces at certain angles of incidence

Question 24

What are two applications of polarised electromagnetic waves?

Answer 24

For sunglasses and goggles which reduce eyestrain and allow people to see through water or off snow more effectively. For radio waves where interference needs to be reduced so plane polarised waves are picked up by receivers with the same alignment

Question 25

What is refraction?

Answer 25

The change in direction at a boundary between one medium and another

Question 26

What is the refractive index?

Answer 26

The ratio of a wave’s speed between two materials. It is normally quoted for light travelling in a vacuum into a material

Question 27

What does it mean if a material has a higher refractive index than another material?

Answer 27

The light travelling through it bends a more significant amount in the material with the higher refractive index. Essentially, the implication is that the material with the higher refractive index is denser than the other one

Question 28

What is the formula for refractive index and what are its units?

Answer 28

refractive index (n) = speed of light in a vacuum (c) / speed of light in the material (cs), since refractive index is a ration, it has no units

Question 29

What is Snell’s Law?

Answer 29

Refractive index of M1 x sin (angle of incidence in M1) = Refractive index of M2 x sin (angle of refraction in M2)

Question 30

When total internal reflection happens, is the boundary the light is attempting to enter one where the light is going from high to low refractive index or low to high?

Answer 30

High refractive index to low refractive index

Question 31

How does a step index optical fibre work?

Answer 31

The core has a uniform refractive index and the cladding a lower refractive index, causing repeated total internal reflection and thus the transmission of light

Question 32

Why does diversion happen?

Answer 32

As different colours of light travelling through the glass slow down by differing amounts since the refractive index is different for each of the wavelengths. This is why you can see each of the different colours separated from white light in a glass prism

Question 33

What are the two types of dispersion that take place within step index optical fibres?

Answer 33

Modal and material dispersion

Question 34

What is pulse broadening and what causes it?

Answer 34

When the duration of a pulse increases due to different wavelengths of light travelling at different speeds - thus a sharp pulse separates over distance into a broader signal

Question 35

What happens in modal dispersion?

Answer 35

Rays within the fibre take different paths and thus pulse broadens

Question 36

What happens in material dispersion?

Answer 36

Different wavelengths of light travel at varying speeds within the fibre thus the pulse broadens

Question 37

What can absorption of light within an optical fibre cause in terms of signals?

Answer 37

A weakening of the signal, resulting in it often needing to be boosted or amplified over long travelling distances in the optical fibre

Question 38

What has more energy, long wavelength radio waves or shorter wavelength X-rays and why?

Answer 38

The X-rays have more energy since the energy of a photon is inversely proportional to its wavelength