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REFRACTION OF LIGHTFrom principles to applications
What is refraction?
□This refers to the bending of light due to difference in transmitting medium.
□The degree of refraction is affected by the nature of the medium.
Snell’s Law
□A law that describes mathematically the relationship between the angles of incidence and refraction
□n1sinθi = n2sinθr
Snell’s Law
Index of Refraction
□A value that describes how light travels in a medium.
□It is simply the ratio of the velocity of light in vacuum over the velocity of light in a medium.
□n = c/v□c = 3 x 108 m/s
Index of Refraction of Some Materials
Medium Index of refraction (n)
Vacuum 1.0000
Air 1.0003
Water 1.33
Ethyl alcohol 1.36
Fused quartz 1.46
Crown glass 1.52
Light flint 1.58
Lucite 1.51
Sodium chloride
1.53
Diamond 2.42
Rule of the thumb…
□Index of refraction of a material is inversely proportional to the velocity of light
□Therefore, if light travels in a medium with HIGH index of refraction, light SLOWS DOWN
Total Internal Reflection
Fiber optics
Fiber optics
Fiber optics
Binoculars and periscopes
Sample Problems on Snell’s Law
□A flashlight beam strikes the surface of apane of glass (n = 1.58) at a 63° angle to the normal. What is the angle of refraction?
□A diver shines a flashlight upward beneath the water at a 42.5° angle to the vertical. At what angle does the light leave the water?
Sample Problems on Snell’s Law
□An aquarium filled with water has flat glass sides whose n = 1.52. A beam of light from outside the aquarium strikes the glass at 43.5° angle to the perpendicular. What is the angle of this light ray when it enters □(a) glass?□(b) water?
Sample Problems on Snell’s Law
□The critical angle for a certain liquid-air surface is 47.7°. What is the index of refraction of the liquid?
LENSESApplications of refraction
What is a lens?
□Any transparent substance or material shaped so as to focus or spread light rays that pass through it for the purpose of forming an image.
Types of lens
CONVERGING OR CONVEX LENS
DIVERGING OR CONCAVE LENS
Family of Lens
Family of Lens
RAY TRACINGImages formed by lenses
Ray Tracing for Lenses
Object beyond 2F
Image is real, inverted and diminishedExample: Camera
Object at 2F
Image is real, inverted the same size as the objectExample: Photocopier
Object between C and F
Image is real, inverted and enlargedExample: Overhead projector
Object at F
No image is formed. Example: Lighthouse spotlight
Object between F and O
Virtual, upright and enlargedExample: Magnifying glass
For images formed by concave lens
Always virtual, upright and diminished
LENS EQUATIONMathematical approach
Lens Equation
Sign Convention for Lenses
Lens f do di
Real Virtual
Convex + + + -
Concave - + -
Sample Problems on Lens Equation
□What is the position and size of the image of a 7.6-cm high flower placed 1 m from a 50 mm focal length camera lens (convex)?
Sample Problems on Lens Equation
□Where must a small insect be placed if 25 cm focal length diverging lens is to form a virtual image 20 cm in front of a lens?
Sample Problems on Lens Equation
□A stamp collector uses a converging lens with focal length 24 cm to view a stamp 18 cm in front of the lens. □a. Where is the image located? □b. What is the magnification?
Sample Problems on Lens Equation
□An object is placed 10 cm from a 15-cm focal length converging lens. Determine the image position and size.
Sample Problems on Lens Equation
□An object is placed 12 cm from a lens with 15 cm focal length. Will the image be real or virtual if the lens is (a) converging (b) diverging?
THE LENSMAKER’S EQUATION
Beyond thin lenses
In cases like this…
Lensmaker’s Equation
Sample Problems on Lensmaker’s Equation
□A convex meniscus lens is made from glass with n = 1.50. The radius of curvature of the convex surface is 22.4 cm, and that of the concave surface is 46.2 cm. What is the focal length?
Sample Problems on Lensmaker’s Equation
□A double concave lens has a surface radii of 34.2 cm and 23.8 cm. What is the focal length is n = 1.52?
Sample Problems on Lensmaker’s Equation
□A Lucite planoconcave lens has one flat surface and the other has R = -18.4 cm. What Is the focal length?