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?