Physics Light 1
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E B 3
Crooke s Radiometer Solar Panels 4
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Pin Hole Camera Object (Candle) Image (Inverted & Size) 6
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Regular Diffuse e.g. mirrors e.g. page 9
Mirror Page 10
Regular Diffuse 11
Plane Concave Convex Spherical 12
IR Incident ray Reflected ray Normal at Angle of incidence Angle of reflection N RR i r 13
1. Same plane IR 2. i = r N i r RR 14
Plane Mirror 15
RB (or Laser) P PM i r H 16
O I Virtual image 17
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Real Rays do pass through the image Virtual Rays do not pass through the image ( they only appear to pass through) 19
Real or Virtual?? Size?? Position?? Erect or Inverted?? Laterally Inverted... 20
Also... Decorative Telescopes. 21
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No parallax between S and image of O S PM v O u u = v i.e.... 23
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C F P P F C 25
C F P C = centre of curvature F = focus P = pole P F C Principle Axis PC = radius of curvature (r) PF = focal length (f) r = 2f 26
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Focus Real or Virtual?? Focus Real or Virtual?? 28
Purpose =?? to locate an image using rays Overall: take 2 rays from the object image is where the 2 reflected rays meet 29
Rays that can be used F F 30
Rays that can be used F P C F 31
Convex Mirror Ray Diagrams Rays that can be used F F 32
P F C 33
Java for the ray diagrams: 34
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Shaving Car headlights Floodlights... Dentists Projectors Cars... rear view Shops Buses Dangerous corners Advantage & Disadvantages... 36
u C F P u v v f P F f 37
u v f 1 1 1 + = Sign Convention u v f v height of image to real = + m = = u height of object to virtual = 38
P1 An object is placed 30 cm in front of a concave mirror of focal length 20 cm. Find the position and nature of the image. 1/u + 1/v = 1/f 1/30 + 1/v = 1/20 1/v = 1/20 1/30 1/v = 3/60 2/60 1/v = 1/60 v = + 60 cm Real 60 cm from mirror in front of mirror 39
P2 An object is placed 12 cm in front of a concave mirror of focal length 20 cm. Find the position, nature and magnification of the image. 1/u + 1/v = 1/f 1/12 + 1/v = 1/20 1/v = 1/20 1/12 1/v = 3/60 5/60 1/v = 2/60 v = 30 cm Virtual 30 cm behind the mirror m = v/u m = ( 30) / (12) m = 2.5 2.5 times higher (virtual) 40
P3 An object placed 15 cm in front of a concave mirror produces a real image which is 30 cm from the front of the mirror. (i) Calculate the focal length of the mirror. (ii) If the object is 5 cm high what is the height of the image? (i) 1/u + 1/v = 1/f 1/15 + 1/30 = 1/f 2/30 + 1/30 = 1/f 3/30 = 1/f f = + 10 cm (ii) height of image m = = height of object height of 5 image = height of image = 30 15 v u 10 cm 41
P4 An image is formed in a concave mirror of focal length 20 cm. The image is three times the size of the object. Where must the object be placed if: (i) the image is real (ii) the image is virtual? (i) v/u = + 3 v = + 3u 1/u + 1/v = 1/f 1/u + 1/3u = 1/20 3/3u + 1/3u = 1/20 4/3u = 1/20 3u = 80 u = 26.67 cm between F and C (ii) v/u = 3 v = 3u 1/u + 1/v = 1/f 1/u + 1/( 3u) = 1/20 3/3u 1/3u = 1/20 2/3u = 1/20 3u = 40 u = 13.33 cm inside F 42
P5 An object is placed 40 cm in front of a convex mirror of focal length 24 cm. (i) At what distance from the mirror will the image be formed? (ii) Find the nature and magnification of the image. (i) 1/u + 1/v = 1/f 1/40 + 1/v = 1/24 1/v = 1/24 1/40 1/v = 5/120 3/120 1/v = 8/120 v = 15 cm 15 cm behind the mirror (ii) Virtual m = v/u m = ( 15)/40 m = 3/8 Image is 3/8ths... 43
P6 A convex mirror of focal length 15 cm forms an image that is one third the size of the object Find the positions of the object and the image. v m = = u 1 3 v = u 3 1 u + 1 v = 1 f 1 u + 1 ( u/3) = 1 15 1 u www.tryscience.org 3 u = 1 15 = 2 u u = 30 cm v = u 3 30 = = 3 10 cm 10 cm behind 44
LB CW S u v Method Sharp image by Measure Result 1/f = 1/u + 1/v Precautions Repeat, other, to average f 45
LB u CM S v LB CW S u v 46
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1/v = 1/f Why? 1/u + 1/v = 1/f 0 + 1/v = 1/f 1/v = 1/f Get average f 1/u = 1/f 1/u + 1/v = 1/f 1/u + 0 = 1/f 1/u = 1/f 48
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An object, 3 cm high, is placed (i) 60 cm, (ii) 25 cm, (iii) 10 cm, from a concave mirror of focal length 20 cm. Calculate the position, nature and size of the image in each case. Concave mirror focus is real => f = +20 cm (i) 1/f = 1/u + 1/v 1/20 = 1/60 + 1/v 1/v = 1/20 1/60 = 3/60 1/60 = 2/60 = 1/30 v = + 30 cm m = v/u = (+30) (+60) = 0.5 height of image = 3 cm x 0.5 = 1.5 cm Ans. 30 cm in front of mirror, real, 1.5 cm high 50
An object, 3 cm high, is placed (i) 60 cm, (ii) 25 cm, (iii) 10 cm, from a concave mirror of focal length 20 cm. Calculate the position, nature and size of the image in each case. (ii) 1/f = 1/u + 1/v 1/20 = 1/25 + 1/v etc v = + 100 cm m = v/u = 100 25 = 4 height of image = 3 cm x 4 = 12 cm Ans. 100 cm in front of mirror, real, 12 cm high 51
An object, 3.0 cm high, is placed (i) 60 cm, (ii) 25 cm, (iii) 10 cm, from a concave mirror of focal length 20 cm. Calculate the position, nature and size of the image in each case. (iii) 1/f = 1/u + 1/v 1/20 = 1/10 + 1/v etc v = 20 cm m = v/u = ( 20) (+10) = 2 height of image = 3 cm x 2 = 6.0 cm Ans. 20 cm behind the mirror, virtual, 6.0 cm high 52
An object, 10 cm high, is place (i) 40 cm, (ii) 15 cm, from a convex mirror of focal length 30 cm. Calculate the position, nature and size of the image in each case. Convex mirror focus is virtual (i) 1/f = 1/u + 1/v 1/30 = 1/40 + 1/v => f = 30 cm 1/v = 1/30 1/40 etc v = 17.1 cm m = v/u = ( 17.1) (40) = 0.43 Size of image = 10 cm x 0.43 = 4.3 cm Ans. 17.1 cm behind the mirror, virtual, 4.3 cm high 53
An object, 10 cm high, is place (i) 40 cm, (ii) 15 cm, from a convex mirror of focal length 30 cm. Calculate the position, nature and size of the image in each case. Convex mirror focus is virtual (ii) 1/f = 1/u + 1/v 1/30 = 1/15 + 1/v etc v = 10 cm m = v/u = ( 10) (40) = 0.25 Size of image = 10 cm x 0.25 => f = 30 cm = 2.5 cm Ans. 10 cm behind the mirror, virtual, 2.5 cm high 54
How far from a concave mirror of focal length 10 cm must an object be place so that the image is 3 times bigger and (i) real, (ii) virtual? (i) Real image => m = + 3 Note: m = v/u = + 3 => v = 3u 1/f = 1/u + 1/v 1/10 = 1/u + 1/3u 1/10 = 3/3u + 1/3u = 4/3u 3u = 40 => u = 13.3 cm between F and C 55
How far from a concave mirror of focal length 10 cm must an object be place so that the image is 3 times bigger and (i) real, (ii) virtual? (ii) Virtual image => m = 3 Note: m = v/u = 3 => v = 3u 1/f = 1/u + 1/v 1/10 = 1/u + 1/( 3u) 1/10 = 3/3u 1/3u = 2/3u 3u = 20 => u = 6.7 cm inside F 56
How far from a convex mirror must an object be placed so that its image is one quarter the size of the object? Convex mirror => Image is virtual => m = 1/4 m = v/u = 1/4 1/f = 1/u + 1/v => v = (u/4) 1/20 = 1/u + 1/( u/4) = 1/u 4/u = 3/u u = 60 cm 57