Crooke s Radiometer. Solar Panels

Transcription

1 Physics Light 1

2 2

3 E B 3

4 Crooke s Radiometer Solar Panels 4

5 5

6 Pin Hole Camera Object (Candle) Image (Inverted & Size) 6

7 7

8 8

9 Regular Diffuse e.g. mirrors e.g. page 9

10 Mirror Page 10

11 Regular Diffuse 11

12 Plane Concave Convex Spherical 12

13 IR Incident ray Reflected ray Normal at Angle of incidence Angle of reflection N RR i r 13

14 1. Same plane IR 2. i = r N i r RR 14

15 Plane Mirror 15

16 RB (or Laser) P PM i r H 16

17 O I Virtual image 17

18 18

19 Real Rays do pass through the image Virtual Rays do not pass through the image ( they only appear to pass through) 19

20 Real or Virtual?? Size?? Position?? Erect or Inverted?? Laterally Inverted... 20

21 Also... Decorative Telescopes. 21

22 22

23 No parallax between S and image of O S PM v O u u = v i.e

24 24

25 C F P P F C 25

26 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

27 ??? 27

28 Focus Real or Virtual?? Focus Real or Virtual?? 28

29 Purpose =?? to locate an image using rays Overall: take 2 rays from the object image is where the 2 reflected rays meet 29

30 Rays that can be used F F 30

31 Rays that can be used F P C F 31

32 Convex Mirror Ray Diagrams Rays that can be used F F 32

33 P F C 33

34 Java for the ray diagrams: 34

35 35

36 Shaving Car headlights Floodlights... Dentists Projectors Cars... rear view Shops Buses Dangerous corners Advantage & Disadvantages... 36

37 u C F P u v v f P F f 37

38 u v f = Sign Convention u v f v height of image to real = + m = = u height of object to virtual = 38

39 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

40 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 = times higher (virtual) 40

41 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 = v u 10 cm 41

42 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 = 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 = cm inside F 42

43 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

44 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) = u 3 u = 1 15 = 2 u u = 30 cm v = u 3 30 = = 3 10 cm 10 cm behind 44

45 LB CW S u v Method Sharp image by Measure Result 1/f = 1/u + 1/v Precautions Repeat, other, to average f 45

46 LB u CM S v LB CW S u v 46

47 47

48 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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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. 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

51 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 = cm m = v/u = = 4 height of image = 3 cm x 4 = 12 cm Ans. 100 cm in front of mirror, real, 12 cm high 51

52 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

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 (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 cm behind the mirror, virtual, 4.3 cm high 53

54 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

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? (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

56 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

57 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