Today’s Topic:

Snell’s Law / Lenses Learning Goal:

Students will be able to calculate the angle

of reflection of a bent light wave.

If you haven’t turned in your Law of

Reflection packet, bring it to the front

table.

Take out your notes from yesterday as

we learn about Snell’s Law.

Homework

Complete The Law of Reflection

Worksheet (One Day Late)

Complete the Snell’s Law Worksheet

(Due Monday, 6/1)

Refraction When light rays pass into a medium with

a higher density, the rays will bend

toward the normal.

The light travels slower

in water, so the wave slows

down and bends towards

the normal.

(Cat looking at Fish)

Refraction When light rays pass into a medium with

a lower density, the light rays will bend

away from the normal.

Light travels faster in air,

so the wave speeds up,

bending it away from the

normal.

(Fish looking at Cat)

Light Bending Now that we know bends as it travels

through different mediums, one might

ask “how much does the light bend?”

The amount light bends is dictated by

Snell’s Law.

Snell’s law is a formula used to describe

the relationship between the angles of

incidence and refraction when light

refracts.

Snell’s Law Snell’s Law:

n𝑖 • sin θ𝑖 = n𝑟 • sin θ𝑟

Where θ𝑖 = angle of incidence

θ𝑟 = angle of refraction

n𝑖 = refractive index of incidence medium

n𝑟 = refractive index of refraction medium

Sample Problem A light ray traveling through air strikes a

smooth, flat slab of crown glass

(n = 1.52) at an angle of 30° to the

normal.

What is the angle of refraction?

19.2049°

Snell’s Law Example Light travels from air (n=1) into an optical

fiber with an index of refraction of 1.44

a) In which direction does the light bend?

b) If the angle of incidence on the end of

the fiber is 22°, what is the angle of

refraction inside the fiber?

Snell’s Law Example a) In which direction does the light bend?

Since the light is going from a low

index of refraction (n=1) to high

(n=1.44), the light is slowing down, so

the light will bend towards normal.

Snell’s Law Example b) If the angle of incidence on the end of

the fiber is 22°, what is the angle of refraction

inside the fiber?

n𝑖*sin θ𝑖 = n𝑟*sin θ𝑟

(1.00)*sin(22°) = (1.44)*sin(θ2)

sin(θ2) = (1.00/1.44)*sin(22°) = 0.260

θ2 = sin−1 (0.260) = 15.0786°

What is a Lens? A lens is a piece of transparent material,

such as glass, that refracts light.

A lens forms an image by bending rays

of light that pass through it.

Where are lenses in this room?

Types of Lenses You can think of a lens as a combination of

many different prisms.

When they are arranged in certain

positions, the prisms bend incoming parallel

rays so they converge or diverge to a single

point.

Converging Diverging