11.3 + 11.4 Reflection, refraction, diffraction, polarisation

Question 1

what is reflection?

Answer 1

when a wave changes direction at a boundary between two media, remaining in the original medium
* wavelength, frequnecy do not change

Question 2

what is a wavefront?

Answer 2

Lines of constant phase

Question 3

what is refracation?

Answer 3

when a wave changes speed as it changes direction at the boundary of two media
* frequnecy the same
* wavespeed and wavelength change

will always be partial reflection

Question 4

what happens when waves moves to denser mediums

Answer 4

• normal waves: speed up, move away from the normal
• EM waves slow down, move towards the normal

Question 5

what is diffraction?

Answer 5

the spreading out of a wave front as it passes through a gap
* hyeogens principle: when a wave is disturbed each point where there is a disturbance becomes a source for a spherical wave

maximim difraction when gap is same size as incident wavelength

Question 6

What is polarisation ?

Answer 6

Can only be done to transverse waves, applying a filter to light

Question 7

What is a plane polarised light?

Answer 7

A transverse wave where oscillations are limited to only one plane

Question 8

What happens when two polarised filters are perfectly aligned ?

Answer 8

Question 9

What happens when two Polaroid filters are at 90° to each other?

Answer 9

Question 10

Describe the use of Polaroid sun glasses

Answer 10

1. light is horizontally polarsied (from water/metal surfaces)
2. sunglasses have vertically alligned filtesr blobking all this polarised light
3. this reduces the bright glare

Question 11

What happens to the wavefronts in diffraction?

Answer 11

Question 12

Describe refraction in terms of wavefronts

Answer 12

Part of wavefronts change speed first causing the change in direction, when at an angle to the normal

Question 13

What are the refraction rules for EM waves and mechanical waves?

Answer 13

Question 14

what are the rules for diffraction?

Answer 14

• wave speed, wavelength: do not change
• the longer the wavelength the more the wave spreads out
• the smaler the gap relative to the wavelength, the greater the diffraction

Question 15

what is polarisation?

Answer 15

• a property of transverse waves
• defines the plane of oscillation of the wave

Question 16

what is the plane of polarisation of an EM wave?

Answer 16

the plane in which the electric field vibrates

Question 17

how is light (EM waves) polarised with filters?

Answer 17

• plane of allignment of the filter is the plane in which E-field oscillations pass through
• transmitted light is polarised in the same plane

allows all components of waves in that certain direction not just E fiel

Question 18

what is unpolarised light?

Answer 18

• **wave trains **(a group of waves of equal or similar wavelengths travelling in the same direction)

Question 19

What is Malus Law?

Answer 19

Question 20

how is light polarised by reflection?

Answer 20

• on metal surfaces and water
• polarised in the horizontal plane

Question 21

How do polarising filters work?

Answer 21

Question 22

Answer 22

• unpolarised light from lamp
• p1 polarises the light in the vertical plane
• p2 polarises light int the horizontal plane
• but there is no component of vertically plane polarised light that lays in the horizontal direction

Question 23

Question 24

when in the maximum intensity emitted from 2 polarising filtres?

Answer 24

when they have no effect ( are alligned in the same plane)

Question 25

Polarising filters MCQ

Answer 25

Question 26

Answer 26

Question 27

What is the wavelength formula?

Answer 27