9.1 Light as a Wave

Question 1

Huygens Principle

Answer 1

Question 2

Images in a plane mirror

Answer 2

Question 3

Real and Virtual Images

Answer 3

• Virtual Image: An image formed behind an optical element such as a mirror is classified as a virtual image
• Real image: Other optical systems form a real image where the rays converge to meet in reality. A real image can be shown on a screen, e.g image from a slide projector. Virtual images cannot be projected on to a screen.
• All images formed by plane mirrors are:
  1. Upright
  2. Same distance behind the mirror as the object is in front
  3. Same size as the object

Question 4

What is refraction

Answer 4

The changing of direction of light as it passes from one medium to another. This is a direct result of the changing speed of the light upon entering that medium of different optical density

Question 5

Why refraction happens

Answer 5

• When light strikes the surface of a medium, some incident light is reflected, some is transmitted, and some is absorbed.
• The transmitted ray deviates from the original direction of travel, occuring at the boundary between the two mediums, called the interface.

Question 6

Refraction of light on parallel sided objects

Answer 6

Question 7

Refraction of light on circular surfaces.

Answer 7

For circular surfaces note that the normal is along the radius of the circle and therefore, i=0 and r=0 as long as the incident ray of light is running along the radius of the circular object.

Question 8

Refraction - density of mediums

Answer 8

• When light moves through a more dense medium, moves slower and refracts towards the normal
• When light moves through a less dense medium, travels faster, refracts away from the normal.

Question 9

Question 10

How does apparent depth work?

Answer 10

Rays from object are frefracted away from the normal at the water-air boundary

Question 11

Mirage

Answer 11

A mirage is a displaced, distorted image that occurs when layers of air of idfferent temperatures bend the path of light. An inferior mirage is the downward displacement of an image. A superior mirage means the image is displaced upwards

Question 12

Question 13

Refractive Index

Answer 13

Amount of refraction depends on how much the speed of light changes as light moves from one medium to another - when light slows down greatly, will undergo significant refraction.
The change in speed of a wave is referred to as the refractive index.
Vacuum: 1
Air: 1
Water: 1.33
Quartz: 1.46
Crown glass: 1.52
Flint glass: 1.62
Diamond: 2.42

Question 14

Refractive index between more than two mediums

Answer 14

Question 15

Snell’s law graphing

Answer 15

When graph of refraction and incident ray are plotted, line begins to curve. Multiplying both by sin will show a straight line. Therefore:

Question 16

Snell’s law

Answer 16

Question 17

Critical Angle

Answer 17

Occurs when light moves from a more dense to a less dense medium and the angle of refraction = 90 degrees

Question 18

Total Internal Reflection

Answer 18

If the angle of incidence is then increased beyond the critical angle no ray is transmitted and total internal reflection will occur. That is : angle r= 0 degrees => NO refraction, no transmitted light and the law of reflection applies here to 100% of the light that entered the medium.

Question 19

Applications of total internal reflection

Answer 19

• Binoculars
• Optical fibres: transmit data via fast-traveling pulses of light
• Flexible fiberscope

Question 20

Dispersion

Answer 20

• Dispersion is the spreading out of white light into component colours
• White light is made up of many different frequencies and therefore wave lenghts, the speed at which light is transmitted in different mediums is slightly different due to different frequencies.

Question 21

Application of Dispersion

Answer 21

• Diamond has a relatively high refractive index of 2.42, therefore the critical angle is relatively small 24 degrees. The shape of diamond disperses the light, the number of internal refractions, single colours of light are scattered
• Rainbows, water droplets in air disperse white light to produce a rainbow.

Question 22

Polarisation

Answer 22

Light is an electromagnetic wave with electric and magnetic fields. These fields vary at a right angle to the direction the wave travels.

Question 23

Techniques for polarising light

Answer 23

• Using polarising filters to convert unpolarised light to polarised light, the fact that light can be polarised suggests that light is a transverse wave, because longitudinal waves cannot be polarised
• These filters have molecules that block electric-field-wave components.
• First image: light wave passes straight through the filter, maintaining original amplitude, all light energy pases through
• Second image: Light wave with electric-field plane completely out of alignment with filter will be block, light is absorbed by filter.

Question 24

Applicaiton of polarised sugnlasses

Answer 24

• One filter may block all the horizontal electric-field components, and other filter may block vertical components.