Quiz 2 Sunday 11 th October Refraction Diffraction

$Quiz 2: Sunday 11 th October ( Refraction & Diffraction) Test 1: Sunday 18$

Quiz 2: Sunday 11 th October ( Refraction & Diffraction) Test 1: Sunday 18 th October (Chapter 13 & 14)-All

REFRACTION Is the bending(change of direction) of light when it passes from one material into another. The speed of light decreases when light enters a dense medium. Refracted ray bends towards the normal. 2

The pencil appears broken when in water. The rays reaching our eyes bend at the surface. The beam bends when it enters glass The fish appears near the surface of water that it real is. Rays from the fish refract at the surface. 3

Coin in Water Coin appears to be near the surface of water Apparent depth Real depth Glass of water 4

Air to glass Glass to Air (Less dense to dense medium) (Dense to less dense) Speed of light decreases and refracted ray Speed of light increase and refracted ray Bends Towards the Normal Bends Away from the Normal A normal is a line drawn 90 o to the surface at the point where the light enters the medium. 5

$Refraction by glass block Exit ray Glass Block y Ra x Bo Incident light$

Refraction by glass block Exit ray Glass Block y Ra x Bo Incident light

$Complete the paragraph below 1. Refraction is caused by the change of ______of light$

Complete the paragraph below 1. Refraction is caused by the change of ______of light when it moves from one material to another. 2. When light moves from less dense to dense material the speed of light______and the refracted ray bends________the normal. 3. Also, when light moves from dense to less dense material the speed of light______. The refracted ray bends_______ the normal. 4. The ratio of speed of light in a material to the speed of light in a vacuum is called_________ of the material. 7

$Boundary Refracted ray Medium 1 Medium 2 Incident ray Which medium is denser. Explain$

Boundary Refracted ray Medium 1 Medium 2 Incident ray Which medium is denser. Explain your answer. 8

$TEACHING POINT ➢Plot a graph of sin i against sin r. ➢Define refractive index$

TEACHING POINT ➢Plot a graph of sin i against sin r. ➢Define refractive index of a material. 9

A graph of sini against sinr is a straight line through the origin. sini The gradient of the graph gives the refractive index(n) sinr 10

Complete the table for sin i and sin r. i/ o r/o sin i sin r 30 20 0. 50 0. 34 35 o 23 o 0. 57 0. 39 40 o 26 o 0. 64 0. 44 45 o 29 o 0. 70 0. 49 50 o 32 o 0. 76 0. 53 55 o 34 o 0. 81 0. 56 60 o 36 o 0. 86 0. 59 Draw graph of sin i (y- axis) against sin r (x-axis) 11

Draw graph of sin i (y-axis) against sin r (x- axis) (0. 68, 1. 0) (0. 14, 0. 2) n = pe o l S Refractive index (n) = 12 = 1. 48

$When the incident angle is 900, no refraction occurs. The rays of light goes$

When the incident angle is 900, no refraction occurs. The rays of light goes straight unchanged 13

$Class work: 1. Write down a formula for refractive index of a material given:$

Class work: 1. Write down a formula for refractive index of a material given: (i) relative speeds (ii) Relative angles (iii) Page 187#13. 14 -13. 16 2. Explain what is meant by (i) Monochromatic light (ii) Critical angle (iii) Total internal reflection (iv) State two conditions for total internal reflection to occur. (V) Page 190#13. 19 -13. 22 3. State one use of total internal reflection 4. Draw a diagram of an optical fibre to show a signal is transmitted 14

$REFRACTIVE INDEX(n) Refractive index is the ratio of speed of light in a vacuum$

REFRACTIVE INDEX(n) Refractive index is the ratio of speed of light in a vacuum to the speed of light in a material. The speed of light in glass 2 x 108 m/s. Calculate the refractive index of glass if the speed of light in air is 3 x 108 m/s n=1. 5 (No units) 15

Exercise 1. Speed of light in 3 x 108 m/s 1. The speed of light a material is 2. 5 x 108 m/s. Find the refractive index of materials. 1. The refractive index of crown glass is 1. 4. Find the speed of light in crown glass. 1. Find the speed of light in a water of refractive index 4/3. 16

Normal Angle of incidence y i ay dr ac te Re fr r a tr n e cid In Air Glass Snell’s Law The ratio of the sine of angle of incidence to the sine of angle of refraction is a constant called refractive index. Angle of refraction 17

Glass to air Air to glass 18

$Normal find refractive index 300 y a tr n e cid In Re fr$

Normal find refractive index 300 y a tr n e cid In Re fr ac te dr ay Air Glass 20 o 19

Normal Find r. 600 y a tr n e cid In Re fr ac te dr ay Air Glass n= 1. 5 r r = sin-1(0. 577) = 35. 20 Angles are always given to 1 decimal place 20

$CRITICAL ANGLE(C): Ø Ø The angle of incidence which gives angle of refraction is$

CRITICAL ANGLE(C): Ø Ø The angle of incidence which gives angle of refraction is 900 when light is travelling from dense to less dense medium Or: Minimum angle at which total internal reflection occurs Watch video Click Link The critical of glass is 420. 21

MONOCHROMATIC LIGHT Light of a single wavelength Example : Laser light

TOTAL INTERNAL REFLECTION(T. I. R) Complete reflection of light when angle of incidence is greater than critical angle when light is traveling from dense to less dense. This occurs when: 1. Light is travelling from dense to less dense medium. The angle of incidence is greater than critical angle. 23

Total internal reflection Watch Video 24

$Calculating Critical Angle r= 90° Air Glass It is possible to calculate the refractive$

Calculating Critical Angle r= 90° Air Glass It is possible to calculate the refractive index using the critical angle c r = 900 i =C n 25

$1. Calculate the critical angle of a glass of refractive index of 1. 5$

1. Calculate the critical angle of a glass of refractive index of 1. 5 1. Calculate the critical angle of a water of refractive index of 1. 3. 2 Calculate the refractive index of a , material whose critical angle is 470. 26

Critical angle of glass in prism 42 o. Draw the path taken by light shown below. A & D Light from air to glass at 90 o. No Refraction B A 450 The angle of incidence of B & C 450 greater than critical angle of 420 Total internal reflection occurs. 450 C 450 D 27

Critical angle of glass in prism 42 o ➢ Light from air to glass at 90 o ➢No Refraction ➢ Light attempting to go from glass to air but angle of incidence greater than critical angle. 450 ➢Total Internal Reflection 450 ➢ Light from glass to air at 90 o ➢No Refraction 28

Applications of Total Internal Reflection 1. Reflective road signs. 2. Optical Fibres used in -communication -Endoscopes -Periscopes Advantages of optical fibres over copper conductors 1. Less interference. 2. cheaper raw material 3. occupy less space / more information (carried) in the same space 4. flexible for inaccessible places/ 5. do not corrode 29

$Optic Fibre Glass cladding of low refractive index 30 Glass core of high refractive$