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SPM Phyiscs - Light
This document provides an overview of light and optics. It discusses that light has wave and particle properties and travels in straight lines. It also describes the wave properties of light including reflection, refraction, diffraction and interference. Optics is defined as the study of light interacting with objects. Key concepts such as the ray model of light, reflection and refraction on different surfaces, the use of lenses, and applications of optical phenomena are explained. Diagrams illustrate these optical principles and definitions of important terms are provided.
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SPM Phyiscs - Light
- 1. Light and Optics Form4 Physics (SPM) – Chapter 5
- 2. Light Electromagnetic radiation thatis 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. Wave properties oflight 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. Optics Study of interactionof 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.
- 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. Reflection Occurs when thedirection 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.
- 9. Two types ofreflection Specular reflection Occurs when light strikes a smooth and shiny surface Diffused reflection Occurs when light strikes an uneven surface
- 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. Key terms ina 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. Reflection on aplane mirror Object u Plane mirror v Image Line of sight
- 13. Properties of imageformed 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. Reflection on aconcave mirror . . F C P
- 15. Reflection on aconvex mirror P . . F C
- 16. A concave mirroris 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. Properties of imagein 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. Applications of reflection Parallaxmirror in measuring instruments Wing and rear view mirrors Periscope Vanity mirror Satellite dish Headlights and torchlight reflectors
- 19. Refraction Phenomenon where thespeed 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. 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. Low density High density r i r i>r Lowdensity High density i i<r
- 22. Refractive Law The incidentray, 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. Refractive Index, n Hasno 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. Total internal reflection Isa 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. Low density Low density r= 90˚ i=c Critical angle, c r > 90˚ High density i>c Total internal reflection High density
- 26. Observations and applicationsof 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.
- 28. Refraction through abiconvex lens F = Focal point C = Optical centre P = Principle axis f = focal length . . F C f . F f . P
- 29. Refraction through abiconcave lens F = Focal point C = Optical centre P = Principle axis f = focal length . . F C f . F f . P
- 30. A concave lensis 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. Properties of imagein 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. Value of f Valueof 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. 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.
- 35. Compound Microscope Construction line Eyepiecelens Objective lens Fo . Fo Fe . . Fe . Image is: •Magnified •Inverted •Virtual
- 36. Telescope Eyepiece lens Construction line Objectivelens Fo . Fo / Fe . Fe . Image is formed at infinity