Today’s Topic Snell’s Law / Lenses › cms › lib02 › NJ01001379 › Centricity ›...
Transcript of Today’s Topic Snell’s Law / Lenses › cms › lib02 › NJ01001379 › Centricity ›...
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