Light Spectrum

Remember when we said that light travels as electromagnetic waves? Well, what is an electromagnetic wave?

• EM wave: coupled, changing electric and magnetic field that travels through space

• EM radiation: energy that is carried, or radiated, in the form of EM waves

• EM spectrum: the entire range of frequencies and wavelengths that make up all forms of EM radiation – Ex: radio waves, microwaves, visible waves, and

x-rays

The Electromagnetic Spectrum

The Electromagnetic Spectrum

• The EMS are transverse waves that carry both magnetic and electric energy. Each type of EMW is defined by its wavelength. Wavelengths range from 104 m (10,000 m) to 10-15 m (0.00000000000001 m).

Radio/TV Waves

• Radio waves come in three types: Frequency modulation (FM), amplitude modulation (AM), and then there are the lowest frequencies, which are used by two way radios, etc.

Radio Waves and Electromagnetic Fields Simulation

Visible Light• The part of the spectrum that we can see

is called visible light. It is the smallest portion of the spectrum.

c = speed of light in a vacuum

= 2.9979 x 108 m/s = 3.0 x 108 m/s

v = f c = f

White Light and Color

Newton’s Light Experiment

So, Newton figured out that white light is composite (made up of other

colors)…but how did he do it?

Not just one prism…

But TWO!

Each color in the spectrum is associated with a wavelength

PRIMARY COLORS

The colors, that when added together, form white

light(Red, Blue, Green)

ADDITIVE COLOR PROCESS

red + blue + green = white

SECONDARY COLORS

The colors, that are formed when two primary colors

are added together(yellow, cyan, magenta)

SECONDARY COLORS

What does it really mean to see color?

Ray Model

Reflection from Smooth and Rough Surfaces

Reflection

Problem

Refraction

An Analogy for Refraction

The Basic Mechanism of Refraction

SNELL’S LAW

rrii nn sinsin

SNELL’S LAW

Indices of Refraction

Example in notes…

rrii nn sinsin

rn1 sinsin

A beam of light of wavelength 550 nm traveling in air is incident on a slab of transparent material. The incident beam makes an angle of 40.0 with the normal, and the refracted beam makes an angle of 26.0 with the normal. Find the index of refraction of the material.

Refraction Summary• If there is no change in index of refraction the

light is not deflected.• As light goes from a low n to a high n it is bent

toward the normal. The greater the difference the greater the deflection.

• As light goes from a high n to a low n it is bent away from the normal. The greater the difference the greater the deflection.

• If the light is incident on the surface of the material along a normal path, there is no deflection.

Dispersion

Index of Refraction Revisited

Dispersion in a Raindrop

Figure 26-38How Rainbows Are Produced

Total Internal Reflection

Critical Angle Equation

sinθc=n2/n1

Try the one in your notes…

How We See Objects

PP P′

Locating a Mirror Image

Spherical Mirrors

Concave and Convex Mirrors

Real vs. Virtual

• Real images are formed by converging light rays.

• Virtual images are formed by diverging light rays.

Principal Rays Used in Ray Tracing for a Concave Mirror

Image Formation with a Concave Mirror

Inside the Focal Point

Principal Rays Used in Ray Tracing for a Convex Mirror

Image Formation with a Convex Mirror

Refraction and the “Bent” Pencil

How is the ray deflected?

Comparing Lenses with a Pair of Prisms

Lenses

Converging Lenses Diverging Lenses

Convex Meniscus

Planoconvex DoubleconvexConcave Meniscus

Planoconcave Doubleconcave

The Three Principal Rays Used for Ray Tracing with Convex Lenses

Rules for lens diagrams

• Converging lenses1. P ray starts parallel then heads toward focal

point

2. F ray starts from or heads toward focal point then goes parallel

3. M ray goes straight through the middle

F F

Where’s The Image?

Where’s The Image?

F F

• Diverging lenses1. P ray starts parallel then heads away from

focal point

2. F ray starts from or heads toward far focal point then goes parallel

3. M ray goes straight through the middle

The Three Principal Rays Used for Ray Tracing with Concave Lenses

Where’s The Image?

F F

Describe the Image

F F

Two Lenses

Thin Lens Equation