Chapter 14Light and Reflection

1

Light is a form of electromagnetic radiation

All electromagnetic radiation travels at c = 3.00 x 108 m/s

c = f

constant

Radio Waves

longest wavelength ˃ 0.3 msmallest frequency f ˂ 109 Hz

Used to transmit radio and tv signals

Microwaves

wavelength 0.3m ˃ ˃ 1 x 10-3mfrequency 1 x 109 Hz ˂ f ˂ 3 x 1011 Hz

Used in radar, ovens and communication (cell phones)

Infraredwavelength 1 x 10-3 m ˃ ˃ 700 nmfrequency 3 x 1011 Hz ˂ f ˂ 4.3 x 1014 Hz

~heat~

Visible Light

wavelength 700 nm (red) ˃ ˃ 400 nm (violet) frequency 4.3 x 1014 Hz ˂ f ˂ 7.5 x 1014 Hz

Ultraviolet (UV) light

wavelength 400 nm ˃ ˃ 60 nmfrequency 7.5 x 1014 Hz ˂ f ˂ 5 x 1015 Hz

Causes tanning and skin cancer

X rays

wavelength 60 nm ˃ ˃ 10-4 nm frequency 5 x 1015 Hz ˂ f ˂ 3 x 1021 Hz

Gamma rays

shortest wavelength 0.1 nm ˃ ˃ 10-5 nmhighest frequency 3 x 1018 Hz ˂ f ˂ 3 x 1022 Hz

Used to treat cancer

Light is an “inverse square” function, brightness decreases by the square of the distance.

Double the distance will be 1/4th as bright

Reflection

Light can have diffuse or specular (regular) reflection

The angle of incidence = the angle of reflection

Image distance = Object distance

Images can be real or virtualReal images can be projected

Concave Mirrors

Principal axis

C, center of curvature

F, focal point

Mirror Equation

1/p + 1/q = 1/f

object distanceimage distance

focal length

Magnification Equation

M = h’/h = -q/p

image height

object heightimage distance

object distance

+ M upright virtual -M inverted real