THIN LENSES

Refraction

What Is Love Light?

Isaac Newton believed light to be a ray of corpuscles (particles), because light travels in a straight line (think inertia!)

Robert Hooke believed light to have the wave-like nature

Newton’s idea prevailed… until over a century after his death…

LIGHT INTERFERES thus it’s a WAVE!

1801 – Thomas Young produces interference of light

Speed of light is finite, constant…

In vacuum, that is…Light is a(n) ______________ waveIt ____________ a medium

In any substance (anything other than vacuum) light slows down… and its rays bend

Light travels through materials at a speed less than its speed in vacuum.

DEFINITION OF THE INDEX OF REFRACTION

The index of refraction of a material is the ratio of the speed of light in a vacuum to the speed of light in the material:

v

cn

material in thelight of Speed

in vacuumlight of Speed

nr > ni (faster to slower!)

nr < ni (slower to faster)

SNELL’S LAW OF REFRACTION

When light travels from a material withone index of refraction to a material witha different index of refraction, the angleof incidence is related to the angle ofrefraction by

2211 sinsin nn

SNELL’S LAW

Example 1 Determining the Angle of Refraction

A light ray strikes an air/water surface at anangle of 46 degrees with respect to thenormal. Find the angle of refraction whenthe direction of the ray is (a) from air towater and (b) from water to air.

54.0

33.1

46sin00.1sinsin

2

112

n

n 332

96.0

00.1

46sin33.1sinsin

2

112

n

n 742

LAB

Determine the index of refraction of a certain plastic

Materials:

Internal Reflection

When light passes from a medium of larger refractive index into oneof smaller refractive index, the refracted ray bends away from the normal.

Critical angle21

1

2 sin nnn

nc

Find critical angle for

1) diamond2) water3) ice

LAB 2

Calculate critical angle and check it experimentally

Materials: