a difficult question, thousands of years in understanding. very difficult to study, since it cannot...

Light Waves

The Electromagnetic Spectrum

What is Light?

A difficult question, thousands of years in understanding.

Very difficult to study,since it cannot becaught, and it is verydifficult to measure.

What is Light?

Light is a wave that travels through the universe’s electromagnetic field. Electromagnetism = a combination of

electricity and magnetism

Light waves do notneed a physical medium like air.

Properties of Light

Frequency – light is caused by the vibrations of electrons

Wavelength – light waves have crests and troughs, just like water waves

Speed – the speed of light depends on what it is traveling through.

Speed of Light (in a vacuum)

299, 792, 485 m/s ≈ 3 x 108 m/s

186,282 miles per second

671 million miles per hour

Can be slowed if passing through water, glass, etc.

Types of Light

Most light is invisible, because it has frequencies that our eyes cannot see.

Light with faster frequencies has shorter wavelengths and higher energy

Speed = wavelength x frequency

Wavelength = 3 x 108 m/s ÷ frequency

Types of light

TypeBallpark Frequen

cy

Ballpark Wavelen

gth

Radio (AM) 106 Hz 300 m invisible

Radio (FM) 108 Hz 3 m invisible

Microwaves & Radar 1010 Hz 3 cm invisible

Infrared 1013 Hz .03 mm invisible

Types of light

Type Ballpark Frequency

Ballpark Wavelen

gth

Visible 4.4 x 1014 Hz 700 nm Red

4.9 x 1014 Hz 600 nm Orange

5.1 x 1014 Hz 580 nm Yellow

5.8 x 1014 Hz 530 nm Green

6.3 x 1014 Hz 470 nm Blue

6.9 x 1014 Hz 430 nm Indigo

7.4 x 1014 Hz 390 nm Violet

Types of light

TypeBallpark Frequen

cy

Ballpark Wavelen

gth

Ultraviolet 1016 Hz 3 x 10-8 m invisible

X-Rays 1017 Hz 3 x 10-9 m invisible

Gamma Rays (from

space)1018 Hz 3 x 10-10 m invisible

??? More? Smaller? invisible

A Spectrum is a continuous range

Another Diagram

Notice this backwards (?) diagram

The NECAP Version

It’s a Spectrum!

The only difference between types of light is how fast it vibrates (frequency)

Radio waves, visible light, and x-rays are all waves created by vibrating electrons at different speeds

Light can act like a wave!

It can reflect! Reflection = bouncing off

Light can act like a wave!

It can refract! Refraction = bending when it passes through

Light can act like a wave!

It can disperse! Dispersion = separating frequencies of light

Light can act like a wave!

It can diffract! Diffraction = spreading out and separating (by frequency)

Summary 1/3

Light is a wave.

Light has frequency and wavelength.

The speed of light in a vacuum is 3 x 108 m/s.

It is the second fastest thing in the universe (only bad news travels faster).

Summary 2/3

There are many types of light, which all differ only by frequency/wavelength

Faster frequency = shorter wavelength = more energy

In order: Radio, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma Rays

Summary 3/3

Light reflects (bounces off of objects), like on a mirror

Light refracts (bends while passing through objects), like through a glass

Light diffracts (spreads out and separates by wavelength), like making a rainbow