Unit C: Electromagnetic Unit C: Electromagnetic EnergyEnergy

Chapter 2: Electromagnetic Chapter 2: Electromagnetic spectrumspectrum

2.1- Electromagnetic Radiation 2.1- Electromagnetic Radiation (EMR)(EMR)

Defined as a wave with a changing Defined as a wave with a changing electric and magnetic field electric and magnetic field perpendicular (90°) to each otherperpendicular (90°) to each other

EMR is all the energy from the sun.EMR is all the energy from the sun. Waves transmit energy from one Waves transmit energy from one

location to another through location to another through vibrations; in EMR the fields vibrate vibrations; in EMR the fields vibrate and energy is transferred in space.and energy is transferred in space.

EMREMR

waves

1) Wave terminology1) Wave terminology

Transverse- vibrations are perpendicular to Transverse- vibrations are perpendicular to the motion of wave.the motion of wave.

Longitudinal- vibrations are in the same Longitudinal- vibrations are in the same direction of motion.direction of motion.

Crest- the highest point of the wave.Crest- the highest point of the wave. Trough- the lowest point of the wave.Trough- the lowest point of the wave. Cycle- one complete vibration (1 crest and Cycle- one complete vibration (1 crest and

1 trough).1 trough). Wavelength (Wavelength (λλ) – length of 1 cycle.) – length of 1 cycle. Frequency Frequency (( )-)- number of cycles per number of cycles per

second.second.

Types of WavesTypes of Waves

JAVA APPLET

Longitudinal waves

Transverse Wave and Longitudinal Waves

Transverse Waves-1 Transverse Wave

2) Universal Wave equation2) Universal Wave equation

Applies to all types of waves; speed Applies to all types of waves; speed is always the speed of light (c = 3.00 is always the speed of light (c = 3.00 x10x1088 m/s). m/s).

Used to calculate speed, wavelength Used to calculate speed, wavelength or frequency.or frequency.

Where v = speed (m/s)

= wavelength (m)

= frequency (Hz)

ExampleExample An excited atom in a neon sign An excited atom in a neon sign

emits EMR with a wavelength of 6.4 emits EMR with a wavelength of 6.4 x10x10-7-7 m. m.

1) Calculate the frequency.1) Calculate the frequency.

2) If the sign is 25.0m from a person, 2) If the sign is 25.0m from a person, how long will it take for light to how long will it take for light to reach them?reach them?

3) The Electromagnetic spectrum3) The Electromagnetic spectrum

The complete range of EMR; The complete range of EMR; arranged using arranged using and . .

Classifying the different types is done Classifying the different types is done using:using:

- Nature of the source.- Nature of the source.

- Energy transmitted- Energy transmitted

- Effect on living tissue.- Effect on living tissue.

Electromagnetic Spectrum

a) Radio wavesa) Radio waves Lowest frequency; highest Lowest frequency; highest Produced by electrons Produced by electrons

vibrating in circuits; used for vibrating in circuits; used for communications.communications.

Can not penetrate metal = Can not penetrate metal = antennas.antennas.

Types:Types:• ELF ( emitted from circuits at ELF ( emitted from circuits at

60Hz)60Hz)• Waves with Waves with = 4m used for

MRI’s. Do not harm body tissue (low

energy)

radio waves

b) Microwavesb) Microwaves

Used for radar (higherUsed for radar (higher ) ), , satellites and cooking food satellites and cooking food (lower (lower ). ).

Transmit more energy than Transmit more energy than radio waves; radio waves; = 100 GHz. = 100 GHz.

Effects:Effects:• Living tissue has a high % of Living tissue has a high % of

water; can harm tissues water; can harm tissues (especially eye lenses).(especially eye lenses).

c) Infrared radiation (IR)c) Infrared radiation (IR) Causes molecules to vibrate = Causes molecules to vibrate =

heat.heat. Waves with a Waves with a = 4.3 x10 = 4.3 x101111 Hz Hz Skin sensors can detect IR Skin sensors can detect IR

using heat receptors; energy is using heat receptors; energy is not seen, it is felt.not seen, it is felt.

Used for PDA’s; the IR is Used for PDA’s; the IR is “beamed” to the device using “beamed” to the device using a transmitter; received using a a transmitter; received using a receiver (Wii).receiver (Wii).

d) Visible Lightd) Visible Light Complete range of all Complete range of all

colors that can be seen colors that can be seen by the eye (ROYGBIV).by the eye (ROYGBIV).

Vision limits= violet Vision limits= violet ((= 400 nm) and Red = 400 nm) and Red ((= 700nm).= 700nm).

Visible light is emitted Visible light is emitted by things that are hot.by things that are hot.

Light is not a wave, but Light is not a wave, but a photon (packet of a photon (packet of energy); the higher energy); the higher = = lower Energy.lower Energy.

PhotosynthesisPhotosynthesis

Plants use visible light Plants use visible light photons and absorb photons and absorb the energy in order to the energy in order to grow.grow.

Photon is absorbed by Photon is absorbed by chlorophyll and the chlorophyll and the energy is used to energy is used to convert Carbon convert Carbon dioxide and water to dioxide and water to sugar.sugar.

e) Ultraviolet (UV) Radiatione) Ultraviolet (UV) Radiation

Emitted by very hot objects; Emitted by very hot objects; = 1 x10= 1 x101818 Hz. Hz.

Photons have more energy Photons have more energy than visible light; this can than visible light; this can cause cancer/premature cause cancer/premature aging.aging.

Divided into 3 types:Divided into 3 types:• UVA/B- high energy; protect UVA/B- high energy; protect

using sunglassesusing sunglasses• UVC- absorbed by ozone layer UVC- absorbed by ozone layer

(stratosphere); causes DNA (stratosphere); causes DNA mutations that can lead to death mutations that can lead to death (ionizing radiation).(ionizing radiation).

f) X-raysf) X-rays High energy waves; High energy waves; = 10 = 1021.21.

Created when electrons strike Created when electrons strike metal; produced using a high metal; produced using a high voltage tube.voltage tube.

Penetrate skin easily (dark), are Penetrate skin easily (dark), are absorbed into bones (white) = dark absorbed into bones (white) = dark and light image.and light image.

Powerful form of ionizing radiation; Powerful form of ionizing radiation; cause deadly DNA mutations.cause deadly DNA mutations.

ALARA – keeping the radiation ALARA – keeping the radiation exposure as low/short as possible.exposure as low/short as possible.

g) Gamma Radiationg) Gamma Radiation

Highest energy Highest energy radiation; shortest radiation; shortest ..

Are radioactive Are radioactive photons (from photons (from radioactive decay).radioactive decay).

Are ionizing radiation; Are ionizing radiation; cause DNA mutations cause DNA mutations very quickly.very quickly.

Radioactivity

2.2) Astronomy2.2) Astronomy The science of The science of

objects/phenomena that objects/phenomena that originate outside Earth’s originate outside Earth’s atmosphere.atmosphere.

Stars emit EMR; we can study Stars emit EMR; we can study them using Telescopes.them using Telescopes.

The closest star to earth is the The closest star to earth is the sun: Under high temperatures sun: Under high temperatures (15 000 000 °C) and pressures (15 000 000 °C) and pressures nuclei fuse together forming 1 nuclei fuse together forming 1 nucleus (nuclear fusion).nucleus (nuclear fusion).

Nuclear fusion results in the Nuclear fusion results in the release of a helium nucleus and release of a helium nucleus and gamma photons.gamma photons.

Sun

a) EMR emitted by the Suna) EMR emitted by the Sun

Then energy from the photon released in Then energy from the photon released in nuclear fusion is absorbed and then nuclear fusion is absorbed and then reemitted.reemitted.

Made up of Visible light and IR Made up of Visible light and IR (temperature at surface = 6000°C)(temperature at surface = 6000°C)

Emits all EMR; hottest parts (core) emits Emits all EMR; hottest parts (core) emits the highest energy EMR.the highest energy EMR.

Solar flares = eruption in sun’s Solar flares = eruption in sun’s atmosphere due to magnetic fields; emits atmosphere due to magnetic fields; emits mostly X-rays and gamma rays.mostly X-rays and gamma rays.

b) Earth’s atmosphereb) Earth’s atmosphere

Atmosphere filters all EMR except Atmosphere filters all EMR except radio waves and EMR close to the radio waves and EMR close to the visible spectrum from reaching earth.visible spectrum from reaching earth.

Gases that absorb radiation:Gases that absorb radiation:• Oxygen/ozone = UV radiationOxygen/ozone = UV radiation• HH220/CH0/CH44/ CO/ CO22 = IR = IR • Mesosphere/ionosphere atoms = X-rays Mesosphere/ionosphere atoms = X-rays

and gamma rays.and gamma rays.• Electrons = long wave radio waves.Electrons = long wave radio waves.

Earth

c) Properties of lightc) Properties of light

Refraction = bending of light.Refraction = bending of light. Reflection = wave bounces off Reflection = wave bounces off

surface.surface. Polarization = forcing a wave to Polarization = forcing a wave to

vibrate (move) in only 1 directionvibrate (move) in only 1 direction Diffraction = bending of a wave as it Diffraction = bending of a wave as it

passes through an object/opening.passes through an object/opening.

Refraction and Diffraction

Reflection

Refraction

Diffraction

Polarization

d) Telescopesd) Telescopes EMR emitted from the sun provides EMR emitted from the sun provides

information; the first telescope was information; the first telescope was invented 400 years ago and studies invented 400 years ago and studies EMR.EMR.

3 types of telescopes:3 types of telescopes:

1.1. RefractingRefracting

2.2. ReflectingReflecting

3.3. MultiwavelengthMultiwavelength

Telescopes

1) Refracting Telescopes1) Refracting Telescopes First developed by GalileoFirst developed by Galileo Uses 2 lenses (concave and convex).Uses 2 lenses (concave and convex). Problems:Problems:

• Quality of glass is very low.Quality of glass is very low.• Opening was too small.Opening was too small.• Diffraction caused errors in distance to Diffraction caused errors in distance to

the sources of EMR.the sources of EMR.

Galileo Galilei

2) Reflecting Telescopes2) Reflecting Telescopes Uses a curved mirror Uses a curved mirror

that focuses using that focuses using reflection.reflection.

Advantages:Advantages:• Mirrors do not separate Mirrors do not separate

light into colors like light into colors like lenses do = higher lenses do = higher resolution.resolution.

• Large openings = less Large openings = less diffraction.diffraction.

• Mirror can be supported Mirror can be supported from underneath; from underneath; maintains shape.maintains shape.

• Used to gather Visible Used to gather Visible light, IR and UV light, IR and UV radiation.radiation.

c) Multiwavelength telescopesc) Multiwavelength telescopes Advanced reflecting Advanced reflecting

telescopes that are at high telescopes that are at high altitudes or orbiting the altitudes or orbiting the earth.earth.

Gathers as many types of Gathers as many types of EMR as possible; differences EMR as possible; differences in telescopes based on type in telescopes based on type of radiation absorbed.of radiation absorbed.

RadioRadio waves = huge dish waves = huge dish (largest (largest ); produce lots of ); produce lots of diffraction--- use many radio diffraction--- use many radio telescopes to collect data.telescopes to collect data.

X-rays = Chandra X-ray X-rays = Chandra X-ray telescope uses 2 mirrors telescope uses 2 mirrors and an X-ray.and an X-ray.

d) Analyzing starlightd) Analyzing starlight

Scientists use prisms or diffraction Scientists use prisms or diffraction gratings to analyze the EMR into gratings to analyze the EMR into wavelengths.wavelengths.

Objects at 6000°C emit mostly visible Objects at 6000°C emit mostly visible light; create a “rainbow” or colors called light; create a “rainbow” or colors called the continuous spectrum.the continuous spectrum.

Beyond the sun, the spectrum is not Beyond the sun, the spectrum is not continuous but has dark lines where continuous but has dark lines where radiation has been absorbed = radiation has been absorbed = Dark-line/absorption spectrum.Dark-line/absorption spectrum.

spectrumsspectrums Start spectrums can be used to determine what Start spectrums can be used to determine what

gases are in the star.gases are in the star. When current is forced through a gas, the gas When current is forced through a gas, the gas

emits wavelengths = emission or bright-line emits wavelengths = emission or bright-line spectrum.spectrum.

Spectra are analyzed using a Spectra are analyzed using a spectroscope/spectrometer; a diffraction grating spectroscope/spectrometer; a diffraction grating attached to a device that calculates attached to a device that calculates ..

neon lights

Rainbows

e) Doppler Shifte) Doppler Shift

Doppler effect: the frequency of sound Doppler effect: the frequency of sound changes as the source moves toward/away changes as the source moves toward/away from the observer.from the observer.• Towards = higher frequency.Towards = higher frequency.• Away = Lower frequency.Away = Lower frequency.

The same effect happens with EMR:The same effect happens with EMR:• Blue shift = higher frequencies, moves Blue shift = higher frequencies, moves

towards.towards.• Red shift = lower frequencies; moves away.Red shift = lower frequencies; moves away.

Doppler Effect

sound demo

f) Life Cycle of a Starf) Life Cycle of a Star

1.1. Formation of a StarFormation of a Star• Space has some gases Space has some gases

and dust in itand dust in it• Over millions of years, Over millions of years,

gravitational forces gravitational forces between the dust and between the dust and gas result in NEBULA, gas result in NEBULA, large highly compressed large highly compressed cloudsclouds

• Gravitational forces Gravitational forces continue and stars are continue and stars are born in NEBULAEborn in NEBULAE

Aliens

2. STABLE PHASE OF A STAR2. STABLE PHASE OF A STAR• Called Main Sequence StarCalled Main Sequence Star• Gravity created heat and pressure to fuel Gravity created heat and pressure to fuel

fusion reactionsfusion reactions• Larger stars have shorter lifespans:Larger stars have shorter lifespans:

FFgg big big pressure big pressure big more heat more heat rapid fusion rxns rapid fusion rxns run out of fuel run out of fuel

3. Death of a Star3. Death of a Starrun out of Hydrogen their run out of Hydrogen their

main fuelmain fuel

Gravity causes core to Gravity causes core to collapsecollapse

Heat is generated causing Heat is generated causing expansion of outer coreexpansion of outer core

Expansion leads to coolingExpansion leads to cooling

The cooler larger star is The cooler larger star is called a called a RED GIANTRED GIANT

After the Red GiantAfter the Red Giant

Medium Sized Medium Sized Stars Stars

(up to 1.5x sun)(up to 1.5x sun) become WHITE become WHITE

DWARF DWARF a stable star with a stable star with

no fuel that no fuel that radiates left over radiates left over heatheat

Giant StarsGiant Stars SUPERNOVA SUPERNOVA

results in a results in a BLACKHOLE, an BLACKHOLE, an area so dense area so dense with such strong with such strong gravity not even gravity not even light can escapelight can escape

Huge Sized StarsHuge Sized Stars (1.5 – 3x sun)(1.5 – 3x sun)

Massive short lived Massive short lived explosion called explosion called SUPERNOVA blows away SUPERNOVA blows away outer layer of starouter layer of star

NEUTRON STAR results (Pulsar is NEUTRON STAR results (Pulsar is one star that emits radio waves)one star that emits radio waves)

Black Holes

Summary: Life Cycle of a StarSummary: Life Cycle of a Star

NebulaMain

Sequence Star

White Dwarf

Huge stars

Giant stars Supernova

Supernova

Black Hole

Neutron Star

(eg Pulsar)

RedGiant

Medium starsLife Cycle of Stars