The Nature of Light

The Nature of Light

Chapter 22-1

What is Light? Light does not require matter through

which to travel. Light is an electromagnetic wave (EM wave). An electromagnetic wave is a wave that can travel through empty space or matter and consists of changing electric and magnetic fields.

Electromagnetic waves are made of vibrating electric and magnetic fields. 

How EM Waves Are Produced Vibration of an electric field and a

magnetic field together produces an EM wave that carries energy.

The transfer of energy as electromagnetic waves is called radiation. 

The Speed of Light Scientists have yet to discover

anything that travels faster than light. In the vacuum of space, the speed of

light is about 300,000,000 m/s, or 300,000 km/s.

Light can travel about 880,000 times faster than sound! (thunder/lightning)

Light from the SUN! Even though light travels quickly, it

takes about 8.3 min for light to travel from the sun to Earth. It takes this much time because Earth is 150,000,000 km away from the sun.

The EM waves from the sun are the major source of energy on Earth.

What are some examples?

22-2 Electromagnetic Spectrum

Characteristics All EM waves travel at the same

speed in a vacuum—300,000 km/s. How is this possible? The speed of a wave is found by multiplying its wavelength by its frequency. So, EM waves having different wavelengths can travel at the same speed as long as their frequencies are also different.

Radio Waves Radio waves cover a wide range of waves in the EM

spectrum. Radio waves have some of the longest wavelengths and the lowest frequencies of all EM waves. (T.V. is here too)

Microwaves Microwaves have shorter wavelengths

and higher frequencies than radio waves do.

Radar

Microwaves are also used in radar. Radar (radio detection and ranging) is used to detect the speed and location of objects.

Infrared Waves Infrared waves have shorter

wavelengths and higher frequencies than microwaves do.

You can’t see infrared waves, but some devices can detect infrared waves.

Photo taken with film that is sensitive to infrared waves. Brighter colors indicate higher temps

Visible Light Visible light is the very narrow range

of wavelengths and frequencies in the electromagnetic spectrum that humans can see. Visible light waves have shorter wavelengths and higher frequencies than infrared waves do.

Colors of Light

Humans see the different wavelengths of visible light as different colors. The longest wavelengths are seen as red light. The shortest wavelengths are seen as violet light.

The range of colors is called the visible spectrum.

Good vs. Bad Effects of Ultraviolet Light…. GOOD Kill Bacteria Vitamins to our

bodies

BAD Sunburn Cancers Wrinkles Eye Damage

X Rays and Gamma Rays

X rays and gamma rays have some of the shortest wavelengths and highest frequencies of all EM waves

X rays have wavelengths between 0.001 nm and 60 nm. They can pass through many materials. This characteristic makes X rays useful in the medical field

Gamma rays are EM waves that have wavelengths shorter than 0.1 nm. They can penetrate most materials very easily. Gamma rays are used to treat some forms of cancer.

22-3 Interactions of Light

Waves

Reflection Reflection happens when light

waves bounce off an object. The Law of Reflection states that

the angle of incidence is equal to the angle of reflection. Incidence is the arrival of a beam of light at a surface.

Types of Reflection Regular Reflection Diffuse Reflection

Light Source or Reflection? If you look at a TV set in a bright room, you see the

cabinet around the TV and the image on the screen. But if you look at the same TV in the dark, you see only the image on the screen. The difference is that the screen is a light source, but the cabinet around the TV is not.

You can see a light source even in the dark because its light passes directly into your eyes. The tail of the firefly is a light source. Flames, light bulbs, and the sun are also light sources. Objects that produce visible light are called luminous (LOO muh nuhs).

A visible object that is not a light source is illuminated.

Absorption and Scattering The transfer of energy carried by light

waves to particles of matter is called absorption.

Scattering is an interaction of light with matter that causes light to change direction.

Refraction Refraction is the bending of a wave

as it passes at an angle from one substance, or material, to another.

Refraction and Optical Illusions Because of refraction, the cat and the fish see optical

illusions. To the cat, the fish appears closer than it really is. To the fish, the cat appears farther away than it actually is.

Refraction and Color Separation A prism is a piece of glass that

separates white light into the colors of visible light by refraction.

Diffraction Diffraction is the bending of waves

around barriers or through openings. The amount a wave diffracts depends

on its wavelength and the size of the barrier or the opening.

Interference

Interference is a wave interaction that happens when two or more waves overlap. Overlapping waves can combine by constructive or destructive interference.

Constructive and Destructive Interference

We saw this in waves

22-4Light and Color Light and Matter When light strikes any form of matter, it can interact

with the matter in three different ways—the light can be reflected, absorbed, or transmitted.

Types of Matter Matter through which visible light is

easily transmitted is said to be transparent.

Translucent matter transmits light but also scatters the light as it passes through the matter. Wax paper is an example of translucent matter.

Matter that does not transmit any light is said to be opaque (oh PAYK).

Colors of Objects How is an object’s color determined?

Humans see different wavelengths of light as different colors. For example, humans see long wavelengths as red and short wavelengths as violet.

Colors of Opaque Objects

Colors of Transparent and Translucent Objects This bottle is green because the

plastic transmits green light. colored transparent

Mixing Colors of Light Primary colors of light—written in white—combine to

produce white light. Secondary colors of light—written in black—are the result of two primary colors added together.

Color Addition When colors of light combine, you see

different colors. Combining colors of light is called color addition. When two primary colors of light are added together, you see a secondary color of light. The secondary colors of light are cyan (blue plus green), magenta (blue plus red), and yellow (red plus green).

Overhead Notes Here Overhead handout

Pigments and Color A pigment is a material that gives a

substance its color by absorbing some colors of light and reflecting others. Almost everything contains pigments.

Color Subtraction Each pigment absorbs at least one color of light. Look at the

figure below. When you mix pigments together, more colors of light are absorbed or taken away. So, mixing pigments is called color subtraction.

Color Subtraction and Color Printing

Light and Color Television Did you know….. The colors on a color television are

produced by color addition of the primary colors of light. A television screen is made up of groups of tiny red, green, and blue dots. Each dot will glow when the dot is hit by an electron beam. The colors given off by the glowing dots add together to produce all the different colors you see on the screen.