1. 17.1 Reflection and Refraction
Mirrors reflect light and allow us to see ourselves.
A prism is another optical device that can cause light to change directions.
A prism is a solid piece of glass with flat polished surfaces.

2. 17.1 Reflection
Images appear in mirrors because of how light is reflected by mirrors.
The incident ray follows the light falling onto the mirror.
The reflected ray follows the light bouncing off the mirror.

3. Law of Reflection The incident ray strikes the mirror.
The reflected ray bounces off.
The angle of incidence equals the angle of reflection.

4. 17.1 Refraction
When a ray of light crosses from one material to another, the amount it bends depends on the difference in index of refraction between the two materials.

5. 17.1 Index of refraction
The ability of a material to bend rays of light is described by the index of refraction (n).

7. 17.1 Snell's law of refraction
Snell’s law is the relationship between the angles of incidence and refraction and the index of refraction of both materials.
Angle of refraction
(degrees)
Angle of incidence
(degrees)
ni sin Qi = nr sin Qr
Index of refraction of incident material
Index of refraction of refractive material

8. The angle at which light begins reflecting back into a refractive material is called
the critical angle, and it depends on the index of refraction.
The critical angle for water is about 49 degrees.

9. 18.2 Interference, Diffraction, and Polarization
In 1807, Thomas Young ( ) did the most convincing experiment demonstrating that light is a wave.
A beam of light fell on a pair of parallel, very thin slits in a piece of metal.
After passing through the slits, the light fell on a screen.
A pattern of alternating bright and dark bands formed is called an interference pattern.

11. 18.2 Polarization Polarization is another wave property of light.
The fact that light shows polarization tells us that light is a transverse wave.
Most of the light that you see is unpolarized.
That does not mean the light has no polarization.
Unpolarized light is actually an equal mixture of all polarizations.
We call ordinary light unpolarized because no single polarization dominates the mixture.

12. An easy way to think about polarization is to think about shaking a spring back and forth.
If the spring is shaken up and down it makes vertical polarization.
If the spring is shaken back and forth it makes horizontal polarization.
Waves move along the spring in its long direction.
The oscillation of the wave (and its polarization) is transverse or perpendicular to the direction the wave travels.

13. 18.2 Applications of Polarizers
Polarizing sunglasses are used to reduce the glare of reflected light
The LCD (liquid crystal diode) screen on a laptop computer uses polarized light to make pictures.

14. 18.2 Spectrometer
A spectrometer is a device that measures the wavelength of light.
A diffraction grating can be used to make a spectrometer because the wavelength of the light at the first-order bright spot can be expressed in a mathematical relationship.