Early Work – Mar. 6 • List at least three places where you see or use reflections.

Labs • Light and Color • Law of Reflection • Law of Refractions • Everyone turns in a lab • 4 in a group

Early Work – Mar. 8 • What’s the difference between reflection and refraction?

Lab • In groups of four, with six mirrors, align the mirrors at angles so that one object can “see” another object.

– First put butcher paper on top of your desks – After mirrors are aligned, mark mirror placements (with chalk) – Draw the line of sight between each mirror – Measure the angles made with the normal • Write a few sentences about what you discovered doing this lab.

Ch 17 Reflection and Refraction

Demo

Law of Reflection • Angle of Incidence – The angle the incoming beam makes with the normal • Angle of Reflection – The angle the outgoing beam makes with the normal Angle of Incidence = Angle of Reflection

Regular Reflection • When parallel rays hit a smooth surface, such as a mirror, they are reflected in parallel rays

Diffuse Reflection • When parallel rays hit a rough surface, such as the page of a book or a wall, they are reflected in all directions

Refraction • A waves change in direction at a boundary • The beam in the first medium is called the incident ray • The beam in the second medium is called the refracted ray • The angle of refraction is the angle the refracted ray makes with the normal – If the angle of refraction is smaller than the angle of incidence, then the new medium is more optically dense

Snell’s Law • Willebrord Snell, in 1621, wrote – The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant (depending on the medium)

n

= sin sin q

i

q

r

Snell’s Law in General Cases

n i

sin q

i

=

n r

sin q

r

“n” found on P397 in book!

Example • A light beam in air hits a sheet of crown glass at an angle of 30.0

°. At what angle is it refracted?

Index of Refraction and the Speed of Light • The index of refraction is not only a measure of how much the light will bend, – But also of how fast light travels in the medium

n substance

=

c v substance

Example • Find the speed of light in water.

Early Work – Mar. 12 • A ray of light strikes a mirror at an angle of incidence of 28 °. What is the angle of reflection?

• A ray of light has angle of incidence of 25.0

° upon the surface of a piece of quartz. What is the angle of refraction?

Total Internal Reflection

Critical Angle • The critical angle, θ C , of a substance is the incident angle that causes the refracted substance.

θ C , use Snell’s Law

Critical Angle

n i

sin q

i

=

n r

sin q

r n i

sin q

i

=

n r

sin 90

n i

sin q

i

=

n r

sin q

i

=

n r n i

q

i

= arcsin

n r n i

Effects of Refraction • Mirages • Lingering sunlight • Shift of images in liquid

Rainbows

Bkwk • P410: 1, 2, 3, 5, 6, 10, 11, 15, 16, 21, 22, 24, 31, 32, 33, 35, 36, 38, 39, 40, 44, 48, 49, 50, 51, • Ch. 17 Quiz Wednesday! – Must take prior to spring break