Electromagnetic Electromagnetic Spectrum and Spectrum and

LightLight

Chapter 18Chapter 18

Electromagnetic Electromagnetic WavesWaves Transverse WavesTransverse Waves

Consist of constantly changing fieldsConsist of constantly changing fields

electric fieldelectric field – space that exerts – space that exerts electric forces on charged particleselectric forces on charged particles

magnetic fieldmagnetic field – space that – space that produces magnetic forcesproduces magnetic forces

Electromagnetic Electromagnetic Waves…Waves…

Are produced when an electric Are produced when an electric charge vibrates or accelerates.charge vibrates or accelerates.

Can travel without a medium. Can travel without a medium. They can travel through a They can travel through a vacuum, empty space, or matter.vacuum, empty space, or matter.

Speed of LightSpeed of Light

*In a vacuum, the speed of *In a vacuum, the speed of light is 3.00 x 10light is 3.00 x 1088 m/s. m/s.

**All electromagnetic waves **All electromagnetic waves will travel at this speed in will travel at this speed in a vacuum, but they will a vacuum, but they will differ in wavelength and differ in wavelength and frequency!frequency!

Use the formula Use the formula for Wave Speed…for Wave Speed…

to calculate the varying to calculate the varying wavelengths and wavelengths and frequencies.frequencies.

Wave speed = wavelength x Wave speed = wavelength x frequencyfrequency

Is electromagnetic Is electromagnetic radiation a wave of a radiation a wave of a

particle?particle?Travels like a wave with Travels like a wave with

interferenceinterference

Travels in a straight line Travels in a straight line and casts shadows like a and casts shadows like a particleparticle

PhotonsPhotons•The packets of energy The packets of energy that make up that make up electromagnetic electromagnetic radiationradiationThe greater the The greater the frequency the wave frequency the wave has, the more energy has, the more energy each of its photons each of its photons has.has.

Photoelectric Photoelectric EffectEffect

Blue light has a higher frequency Blue light has a higher frequency than red light, so blue light than red light, so blue light photons have more energy.photons have more energy.

Blue light has photons that have Blue light has photons that have enough energy to cause electrons enough energy to cause electrons to be emitted from a metal surfaceto be emitted from a metal surface

The emission of electrons from the The emission of electrons from the metal surface is the metal surface is the photoelectric photoelectric effecteffect

IntensityIntensity

The rate at which a wave’s energy flows The rate at which a wave’s energy flows through a given unit of areathrough a given unit of area

Brightness of the lightBrightness of the light The intensity of light decreases as The intensity of light decreases as

photons travel farther from the source of photons travel farther from the source of the light.the light.

Example: Spray PaintExample: Spray Paint

Electromagnetic Electromagnetic SpectrumSpectrum

Shows the frequencies of Shows the frequencies of electromagnetic radiation electromagnetic radiation increasing from left to rightincreasing from left to right

The spectrum goes from red to The spectrum goes from red to violet: anything beyond the red violet: anything beyond the red band is called infrared radiationband is called infrared radiation

Parts of the EM Parts of the EM SpectrumSpectrum Visible light is the only part that of Visible light is the only part that of

the spectrum that you can see.the spectrum that you can see. The parts of the spectrum include The parts of the spectrum include

radio waves, infrared waves, visible radio waves, infrared waves, visible light, ultraviolet rays, x-rays, and light, ultraviolet rays, x-rays, and gamma rays.gamma rays.

Radio WavesRadio Waves Used in radio, tv, microwave ovens, Used in radio, tv, microwave ovens,

and radarsand radars Longest wavelength and lowest Longest wavelength and lowest

frequencyfrequency Amplitude modulation (AM) – the Amplitude modulation (AM) – the

amplitude of the wave is variedamplitude of the wave is varied Frequency modulation (FM) – the Frequency modulation (FM) – the

frequency of the wave is variedfrequency of the wave is varied

Infrared RaysInfrared Rays Have higher frequencies than radio Have higher frequencies than radio

waves, but lower than red lightwaves, but lower than red light Used as a source of heat Used as a source of heat

(restaurants and zoos)(restaurants and zoos) ThermographsThermographs – color-coded – color-coded

pictures that show variations in pictures that show variations in temperature temperature

Visible LightVisible Light The light that you can see with The light that you can see with

the human eyethe human eye Each wavelength in the visible Each wavelength in the visible

spectrum corresponds with a spectrum corresponds with a frequency and has a particular frequency and has a particular color.color.

ROY G BIVROY G BIV

Ultraviolet RaysUltraviolet Rays Has a higher frequency than violet Has a higher frequency than violet

lightlight Used in medicine and agricultureUsed in medicine and agriculture Moderate exposure helps your skin Moderate exposure helps your skin

produce vitamin Dproduce vitamin D Used to kill microorganismsUsed to kill microorganisms

and help plants grow in a and help plants grow in a

nursery during winternursery during winter

X-RaysX-Rays Used in medicine, industry, and Used in medicine, industry, and

transportation to make pictures transportation to make pictures of the inside of solid objectsof the inside of solid objects

Too much exposure can kill or Too much exposure can kill or damage the living tissuedamage the living tissue

Gamma RaysGamma Rays Have the shortest wavelength and the Have the shortest wavelength and the

highest frequencyhighest frequency Have the most energy and the greatest Have the most energy and the greatest

penetrating abilitypenetrating ability used in the medical field to kill cancer used in the medical field to kill cancer

cells and make pictures of the braincells and make pictures of the brain Also used in industry as Also used in industry as

inspection toolsinspection tools

Without Light Without Light Nothing is Nothing is Visible….Visible….

When you look at When you look at objects, what you are objects, what you are seeing is light.seeing is light.

The behavior of light is The behavior of light is affected by the material affected by the material that it strikes.that it strikes.

TransparentTransparent Allows most of the light to Allows most of the light to

pass throughpass through

You can see clearly through itYou can see clearly through it

Examples: glass, waterExamples: glass, water

TranslucentTranslucent Scatters light that passes Scatters light that passes

through itthrough it

You can see through it, but You can see through it, but not clearlynot clearly

Example: Frosted glassExample: Frosted glass

OpaqueOpaque Absorbs or reflects all of Absorbs or reflects all of

the light that strikes itthe light that strikes it

You can’t see through itYou can’t see through it

Examples: Wood, MetalExamples: Wood, Metal

When light When light strikes a strikes a

medium, it is medium, it is either reflected, either reflected,

absorbed, or absorbed, or transmitted.transmitted.

ReflectionReflection An image is formed from waves that An image is formed from waves that

bounce off of a material’s surfacebounce off of a material’s surface1. Regular Reflection: Image formed is

clearly defined & looks exactly like the object.

Example: mirror

2. Diffuse Reflection: Light scatters in many different directions due to an irregular surface.

If light is transmitted If light is transmitted it can be….it can be…. Refracted: Bending of light from one Refracted: Bending of light from one

medium to another Ex: straw in a cupmedium to another Ex: straw in a cupmiragemirage – false or distorted image – false or distorted image

Polarized: consists of 2 filters that Polarized: consists of 2 filters that block horizontal and vertical waves.block horizontal and vertical waves.Ex. Sunglasses use a Ex. Sunglasses use a

vertical filter to block vertical filter to block horizontal lighthorizontal light

If light is transmitted If light is transmitted it can be….it can be….

Scattered: light is redirectedScattered: light is redirected

when it passes through a when it passes through a mediummedium

Ex: Sunrise and Sunset – red Ex: Sunrise and Sunset – red and orange light is what and orange light is what

makes it to your eyesmakes it to your eyes

PrismPrism Material that diffracts white light

into a color spectrum of light

Dispersion – process of white light separating into colors Ex. Rainbow

Primary colors of light

Red

BlueGreen

All 3 together produce WHITE light

Secondary colors of light

Cyan

Yellow Magenta

Any 2 colors of light that combine to produce white light are complementary colors.

PigmentsPigments Material that Material that

absorb some absorb some colors of light colors of light and reflect the and reflect the other colors.other colors.

Examples: Paint, Examples: Paint, ink, pictures, ink, pictures, and dyeand dye

Primary colors of PIGMENTS

Cyan

Yellow Magenta

All 3 together produce BLACK pigment

Any 2 pigments that form black pigments are complementarypigments

Sources of LightSources of Light

1. Incandescent- Heats a filament until it glows

Ex. Typical light bulb

Sources of LightSources of Light

2. Glowing phosphorus – a phosphor is steadily emitting photons

Ex. Used in schools, hospitals, and offices

Sources of LightSources of Light

3. Laser - Beam of electrons

Sources of LightSources of Light

4. Neon – electrons move through a gas inside a glass tube

Ex. signs

Sources of LightSources of Light

5. Sodium-vapor Light - Contains neon and sodium metalgives off a yellow tint

Ex. Street lights

Sources of LightSources of Light

6. Tungsten-Halogen Light – similar to an incandescent light, but contains halogen gas

Ex. Lamps & headlights