GRADE 11 SUTHERLAND HIGH SCHOOL 2018

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1 GRADE 11 SUTHERLAND HIGH SCHOOL 2018

2 What do you know about Light so far? Light is a form of electromagnetic radiation that comes from the Sun. We see color because of the different frequencies of light that reflects off objects to our eyes. Clear objects are due to the fact that ALL or MOST of the light reaches our eyes. Unclear objects appear that way because some of the light is scattered. Opaque and transparent objects. Laws of Reflection.

4 When light falls on an object, one of the following can occur: 1. It can be transmitted. 2. It can be reflected. 3. It can be absorbed. GO THROUGH EG. GLASS, PERSPEX, WATER COME STRAIGHT BACK EG. MIRRORS TB. pg 127 STAY INSIDE EG. DARK OR COLOURED OBJECTS

5 TB. pg 127 When the surface is shiny and smooth, light will be reflected in a very normal way: THE LAW OF REFLECTION

6 eflection of light The laws of reflection

7 eflection of light The laws of reflection

8 eflection of light The laws of reflection

9 HOMEWORK EXERCISE 9 PG. 128 TB. pg

10 The speed of light is constant in the same medium. If the medium changes, the speed of light will also change. Light has different speeds in different materials: As the density of the medium increases, so light travels slower. TB. pg 129 This is the maximum value for the speed of light.

11 If light strikes the surface of a new medium at right angles to the surface: Change in speed, same direction. If light strikes the surface of a new medium at an angle to the surface: Speed and direction will change. TB. pg

$refraction, but could never derive the full equation.$

12 A roman philosopher and scientist, tried to explain experimentally how light bends as it passes from one light beam to another. He discovered that the angle of incidence is proportional to the angle of refraction, but could never derive the full equation. Like Euclid, Ptolemy thought that light is emitted in rays from the eye.

13 This is the bending of light as it moves from one medium to another medium with a different optical density. TB. pg 131 Optical density: The measure of the speed of light or other electromagnetic waves through a medium.

14 TB. pg 131 When light moves from a less dense medium to a more dense medium to bends TOWARDS the normal.

15 TB. pg 131 When light moves from a more dense medium to a less dense medium to bends AWAY the normal.

16 This is the ratio of the speed of light in air compared to the speed of light through another medium. Refractive index (No unit) Speed of light in air ( m. s 1 ) n = c v TB. pg 135 Speed of light in medium (m. s 1 )

17 TB. pg 135 Refractive Index of different materials

18 Refractive Index is dependent on optical density. n = c v Relationship: Directly proportional. A greater optical density (more dense) means a slower speed through the medium and hence a greater refractive index. TB. pg 136

19 NB! Refraction is due to a change in the speed of a wave in different media. n = c v The frequency of the wave however, remains constant. TB. pg 136

20 EXERCISE 10 PG. 139

$discovered the sin law of refraction.$ $divided by the sine of the angle of refraction is a$ constant number.

21 TB. pg 145 In 1621, Snell, a Dutch mathematician, discovered the sin law of refraction. Snell found that the sine of the angle of incidence divided by the sine of the angle of refraction is a constant number. This constant number is known as the ratio of the two refractive indices of the substances that light travels in. sinθ i sinθ r = n r n i

22 Refractive index of optical medium 1 (No unit) Refractive index of optical medium 2 (No unit) n i sinθ i = n r sinθ r Angle of incidence ( ) TB. pg 145 Angle of refraction ( )

23 If the values were placed on a graph LINEAR RELATIONSHIP DIRECTLY PROPORTIONAL GRADIENT OF A STRAIGHT LINE GRAPH IS CONSTANT THIS CONSTANT VALUE IS THE REFRACTIVE INDEX TB. pg 146

3. More If n i dense < n r, then less θ i dense > θ r. Less.

24 n i sinθ i = n r sinθ r 1. If the values n i and n r 2. If are n similar, then the values i > n of r, then θ θ i and i < θ θ r will r. 3. More If n i dense < n r, then less θ i dense > θ r. Less.away also dense be from similar. more the dense So normal little towards refraction from will the occur. normal TB. pg 146

25 TB. pg 147 PRACTICE ON PIECE OF PAPER

26 TB. pg 147

27 TB. pg 148

28 TB. pg 148 PRACTICE ON PIECE OF PAPER

29 EXERCISE 11 PG. 149

$At this point, the angle of refraction is 90$ critical angle.

30 At this point, the angle of refraction is 90 and the angle of incidence is known as the critical angle. The angle of incidence that provides an angle of refraction of 90-degrees. TB. pg 153

$refracted light will reflected.$

31 Every substance has its own unique critical angle. If If the angle of of incidence is is smaller equal greater to than the than the critical the critical angle angle, in the in the all table, light table, the will part light be will of the be refracted light will reflected. be parallel transmitted TOTAL to the INTERNAL and surface part between REFLECTION will reflected the two back. media. TB. pg 153

32 TB. pg 154 PRACTICE ON PIECE OF PAPER

Light travels from a more dense to a less dense medium. Angle of incidence is greater than the critical angle. Surface acts as a mirror and reflects all the light.

33 Light travels from a more dense to a less dense medium. Angle of incidence is greater than the critical angle. Surface acts as a mirror and reflects all the light. The reflection of light on the inside surface of a medium when light is travelling towards a medium of lower optical density, and the angle of incidence is larger than the critical angle. TB. pg 155

34 TB. pg 155 PRACTICE ON PIECE OF PAPER

35 TB. pg 156

36 The use of TIR MADE OF GLASS. THIN, FLEXIBLE, TRANSPARENT. STRANDS ARE SURROUNDED BY A COATING WITH A LOWER OPTICAL DENSITY AND LOWER REFRACTIVE INDEX. SINCE θ i > CRITICAL ANGLE total internal reflection over and over. Ray of light can travel through the fibre unhindered and emerges with almost the same intensity on the other side. TB. pg 157

37 TB. pg 156 The use of TIR USED BY DOCTORS TO EXAMINE A PATIENT INTERNALLY. ONE BUNDLE WILL CARRY LIGHT TO THE END OF THE TUBE TO ILLUMINATE THE AREA AND THE OTHER WILL REFLECT LIGHT BACK TO THE EYEPIECE. CONNECTED TO A TELEVISON SCREEN TO BE DISPLAYED.

38 The use of TIR OPTICAL FIBRES HAVE ADVANTAGES OVER COPPER WIRES HENCE THEY ARE BEING REPLACED. DO NOT HAVE A RESALE VALUE (WON T GET STOLEN) LIGHTER AND THINNER TRANSFER MORE DATA NOT AFFECTED BY PASSING TB. pg 156 ELECTROMAGNETIC FIELDS. EASIER TO LAY CABLES: EXISTING PIPES.

The use of TIR Huge sections of 8ft wide

up on the Norfolk coast Authorities said

tugged to Algeria for a building project

being taken to North Africa, two more have

Castguard Agency spokesman said the pipes

39 The use of TIR Huge sections of 8ft wide and 1,574ft (480m) long pipe have washed up on the Norfolk coast Authorities said the pipes came loose as they were being tugged to Algeria for a building project There were 12 pipe segments that were being taken to North Africa, two more have washed up at Eccles A Maritime and Castguard Agency spokesman said the pipes pose no danger of pollution Read more: Follow on Twitter DailyMail on Facebook 17 August 2017 TB. pg 156

40 TB. pg 159 EXERCISE 12 PG. 158

SESSION 5: INVESTIGATING LIGHT. Key Concepts. X-planation. Physical Sciences Grade In this session we:

SESSION 5: INVESTIGATING LIGHT Key Concepts In this session we: Explain what light is, where light comes from and why it is important Identify what happens when light strikes the surface of different objects