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# SPM Phyiscs - Light

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### SPM Phyiscs - Light

1. 1. Light and Optics Form 4 Physics (SPM) – Chapter 5
2. 2. Light   Electromagnetic radiation that is perceived by the human eye Has two forms     Waveform Particleform Light travels in the form of rays in a straight line Light rays tend to spread away from the source
3. 3.  Wave properties of light        Reflection Refraction Diffraction Interference Light is a form of energy Visible light is made up of 7 colours of various intensities Light, like any electromagnetic radiation travels through vacuum at a speed of approximately 3X108 ms-1
4. 4. Optics   Study of interaction of light with objects that reflect or scatter light Light is able to    Completely penetrate transparent objects Partially penetrate translucent objects Not penetrate opaque objects
5. 5. Light rays
6. 6. Key notes          Object – material that emits light rays Image – representation of object after light has reflected or refracted Ray diagram – diagram showing path of light through reflection or refraction Line of sight – order or position of the eye to view the image formed Solid lines – real light rays Dotted lines – virtual light rays Convergence – meeting of light rays at a point Divergence – spreading of light rays from a point Focus point – point where light rays are converged or diverged
7. 7. Reflection       Occurs when the direction of light changes when it strikes an opaque material Light ray before reflection – incident ray Light ray after reflection – reflected ray Imaginary line that is perpendicular to surface – normal line Angle of incidence, i – angle between incident ray and normal line Angled of reflection, r – angle between reflected ray and normal line
8. 8. Normal Incident ray i r Reflected ray Plane
9. 9.  Two types of reflection  Specular reflection   Occurs when light strikes a smooth and shiny surface Diffused reflection  Occurs when light strikes an uneven surface
10. 10.  Law of reflection    Incident, reflected ray and normal line lies on the same plane i=r Path of light reflection is represented in a ray diagram
11. 11. Key terms in a ray diagrams       C – centre of curvature of mirrors or optical centre of lenses F – focus point of curved mirrors or lenses f – focal length (distance of F from C) u – distance of object to the surface of reflection or refraction v – distance of image to the surface of reflection or refraction Principle axis, P – light ray that is perpendicular to the surface of reflection or refraction and crosses through C and F * In concave and convex mirrors, C = 2F
12. 12. Reflection on a plane mirror Object u Plane mirror v Image Line of sight
13. 13. Properties of image formed    Same size as object v=u Laterally inverted    Flipped horizontally Left of Object becomes right of Image Virtual   Image exists within the mirror, a.k.a. another plane The image cannot be formed on a screen
14. 14. Reflection on a concave mirror . . F C P
15. 15. Reflection on a convex mirror P . . F C
16. 16.       A concave mirror is also called a converging mirror A convex mirror is also called a diverging mirror The curvier the mirror, the smaller the focal length When incident rays are parallel to P, then reflected rays will pass through F When incident rays passes through F, then reflected rays will be parallel to P When incident rays passes through C, then reflected rays will pass through C in the opposite direction, parallel to the incident ray
17. 17. Properties of image in concave and convex mirrors Location of object Properties of concave image u>C Real, Diminished, Inverted u=C Real, Same size as object, Inverted C<u<F Real, Magnified, Inverted u=F Formed at infinity u<F Virtual, Magnified, Upright Properties of convex image Virtual, Diminished, Upright
18. 18. Applications of reflection       Parallax mirror in measuring instruments Wing and rear view mirrors Periscope Vanity mirror Satellite dish Headlights and torchlight reflectors
19. 19. Refraction     Phenomenon where the speed of light changes as it propagates from one medium to another The change of speed causes a change in the direction of propagation When light propagates from a medium of low density to a medium of high density, its speed decreases, causing the direction of propagation to approach the normal The opposite is true when light passes from a medium of high density to a medium of low density
20. 20.    Incident ray – i Refracted ray – r When light travels from a medium of low density to a medium of high density:     Its speed decreases Its direction changes i>r When light travels from a medium of high density to a medium of low density:    Its speed increases Its direction changes i<r
21. 21. Low density High density r i r i>r Low density High density i i<r
22. 22. Refractive Law   The incident ray, refracted ray and the normal line all lie on the same plane The ratio of sin i to sin r yields a constant known as the refractive index sin i = n, where n = refractive index sin r
23. 23. Refractive Index, n      Has no units Indicates the light bending ability of a medium Value equals to the ratio of sin i to sin r Value also equals to ratio of speed of light in vacuum to speed of light in medium Value also equals to ratio of real depth to apparent depth
24. 24. Total internal reflection      Is a form of light refraction. Occurs when light travels from a medium of high density to a medium of low density, where i > r. Occurs when the i is very large causing the r to be more than 90˚. Critical angle, c is the value of i that results in r = 90˚. When i > c, total internal reflection occurs and the reflected ray is present in the same medium as the incident ray.
25. 25. Low density Low density r = 90˚ i=c Critical angle, c r > 90˚ High density i>c Total internal reflection High density
26. 26. Observations and applications of refraction and total internal reflection         Sunset below the horizon Rainbow formation Mirages Fish’s eye view Fibre optics Prism periscope Prism binoculars Perfectly cut diamond
27. 27. Lenses Bi Bi
28. 28. Refraction through a biconvex lens F = Focal point C = Optical centre P = Principle axis f = focal length . . F C f . F f . P
29. 29. Refraction through a biconcave lens F = Focal point C = Optical centre P = Principle axis f = focal length . . F C f . F f . P
30. 30.        A concave lens is also called a diverging lens. A convex lens is also called a converging lens. The larger the lens, the larger the f value. The thicker the lens, the smaller the f value. When incident rays are parallel to P, then refracted rays will pass through F When incident rays passes through F, then refracted rays will be parallel to P No refraction occurs when incident rays passes through C. The rays simply pass through the lens in a straight line
31. 31. Properties of image in convex and concave lenses Location of object Properties of convex image u=∞ Real, Diminished, Inverted u > 2f Real, Diminished, Inverted u = 2f Properties of concave image Real, Same size as object, Inverted Virtual, Diminished, Upright 2f < u < f Real, Magnified, Inverted u=f Image is formed at infinity u<f Virtual, Magnified, Upright
32. 32.  Value of f    Value of u and v    Positive – convex lens Negative – concave lens Positive – real image Negative – virtual image Lens law     1/f = 1/u + 1/v f = focal length u = object length v = image length
33. 33.  Linear magnification, m    m = v/u m = hi/ho, where hi = height of image and ho = height of object Power of lens, P   P = 1/f Unit = m-1 or Diopter (D)
34. 34. Magnifying glass . . F C . F . P
35. 35. Compound Microscope Construction line Eyepiece lens Objective lens Fo . Fo Fe . . Fe . Image is: •Magnified •Inverted •Virtual
36. 36. Telescope Eyepiece lens Construction line Objective lens Fo . Fo / Fe . Fe . Image is formed at infinity