C11 Waves 1

Question 1

Define Progressive Wave

Answer 1

An oscillation that travels through a medium, transferring energy from one point to another, without permanently displacing any matter.

Question 2

Define Transverse Wave, giving example

Answer 2

• A wave in which the oscillations or vibrations are perpendicular to the direction of energy transfer.
• S-waves, EM waves, water waves

Question 3

Define Longitudinal Wave, giving example

Answer 3

• A wave in which the oscillations or vibrations are parallel to the direction of energy transfer.
• Often called compression waves, they are made of compressions and rarefactions.
• Regions of higher pressure and lower pressure air move, not particles.
• P-waves, sound waves

Question 4

Formula of intensity of a wave

Answer 4

Radiant Power / Surface Area
I = P / A

Question 5

What is phase difference

Answer 5

The difference between the displacement of particles along a wave, measured in degrees (360°) or radians (2π)

Question 6

Antiphase

Answer 6

A phase difference of 180°, or π, where the max positive displacement of one wave is the max negative displacement of another.

Question 7

What is reflection

Answer 7

A wave changes direction at a boundary between two different media, remaining in the original medium.

Question 8

What is refraction

Answer 8

• A wave changes direction as it passes from one medium to another.
• There is always partial reflection when a wave refracts.

Question 9

When do water waves refract, and what happens in shallower water.

Answer 9

• When there is a change in depth.
• When entering shallower water, waves slow down and wavelength shortens.

Question 10

Why are optical microscope limited at a few hundred nanometres?

Answer 10

The diffraction of light as they pass through the apertures in the microscope cannot be avoided at a distance that small.

Question 11

What affects how much diffraction occurs? When is it at its maximum?

Answer 11

• The relative sizes of the wavelength and the gap through which the wave passes through.
• The effect is strongest when the wavelength of the wave is roughly the same size as the gap.

Question 12

What is partial polarisation

Answer 12

• It is when transverse waves reflect off a surface, e.g. light on water.
• There are more waves oscillating in one particular plane, with the water example it is horizontal polarisation.

Question 13

Formula for intensity relating distance

Answer 13

I = P / 4πr^2
That is the surface area of a sphere, as the waves travels outward in all directions like a sphere.

Question 14

Relationship between intensity and amplitude

Answer 14

Intensity is directly proportional to the amplitude^2

Question 15

What is an EM wave?

Answer 15

Transverse waves, which can be thought of as electric and magnetic fields oscillating at right angles to each other.

Question 16

Wavelengths of EM spectrum in metres

Answer 16

Radio: 10^6> to 0.1m
Microwave: 0.1m to 0.001
Infrared: 0.001m to 700nm
Visible: 700nm to 400nm
Ultaviolet: 400nm to 10^-8
X-rays: 10^-10 to 10^-13
Gamma Rays: 10^-13 to <10^-16

Question 17

Wave equation for EM waves

Answer 17

c = fλ
As all EM waves travel at the speed of light in a vacuum.

Question 18

Formula for refractive index

Answer 18

n = c / v
c = speed of light
v = speed of wave through material

Question 19

How to calculate the angle at which light is refracted from one medium to another

Answer 19

n1 sinθ1 = n2 sinθ2

Question 20

Refractive Index of Vacuum, Air, Water, Olive Oil, Crown Glass, Diamond

Answer 20

Vacuum & Air: 1.00
Water: 1.33
Olive Oil: 1.47
Crown Glass: 1.52
Diamond: 2.42

Question 21

What is TIR (Total Internal Refraction)

Answer 21

• Diamond has a very high refractive index. Once light enters, it reflects internally multiple times before leaving.
• When light strikes the boundary at a large angle to the normal, it is totally internally reflected (no light is refracted out).

Question 22

Conditions for TIR

Answer 22

• Light must be travelling through a medium with a higher refractive index than the material on the other side of the boundary.
• Angle at which light to the normal strikes must be > critical angle.

Question 23

Calculating critical angle

Answer 23

sinC = 1 / n