Electromagnetic Spectrum

Keith WarneBHS

Electromagnetic Waves

Electric and magnetic fields always exist …………………….

When ever one is ………………. the other is …………………….

The fields can exist in a …………………...

They are at …….o to each other.

The electromagnetic wave move at ……..o to the fields.

The ……………… of the wave refers to the number of ……………………………

Electromagnetic Waves

Electric and magnetic fields always exist together.

When ever one is collapsing the other is generated.

The fields can exist in a vacuum.

They are at 90o to each other. (Transverse)

They are propagated at 90’ to their own directions.

The frequency of the wave refers to the number of cycles per second

C = 3 x 108 m.s-1

Electromagnetic Waves

……………….

(Signal generated)

………………

(Signal Received)

RH DR

EM waves can be ………………… and detected by changing electric ……………………. in a conductor (arial)

Electromagnetic Waves

Transmitter

(Signal generated alternating

current)

Receiver:

(Signal Received – weak alternating current induced – needs amplification)

Right Hand Dynamo Rule

EM waves can be generated and detected by changing (accelerating) electric currents in a conductor (arial)

Direction of movement

FieldField

CurrenCurrentt

Thrust/movementThrust/movement

Electromagnetic Spectrum

All the different types of electromagnetic waves form the ……………………………………………….

Changing the ………………………. changes the properties of the waves.

Electromagnetic Spectrum

All the different types of electromagnetic waves form the Electromagnetic Spectrum.

Changing the frequency changes the properties of the waves.

INCREASING FREQUENCY and ENERGY

INCREASING W A V E L E N G T H

Radio Waves Radio waves have the

………………… wavelengths in the electromagnetic spectrum.

These waves can be longer than a ………………. or as short as a …………….

Radio waves do more than just bring music to your radio.

They also carry …………. for your ……………… and ………………….. phones

Radio Waves Radio waves have the

longest wavelengths in the electromagnetic spectrum.

These waves can be longer than a football field or as short as a football.

Radio waves do more than just bring music to your radio.

They also carry signals for your television and cellular phones

Microwaves Microwaves have

wavelengths that can be measured in ……………………………!

The longer microwaves, those closer to a ………….. in length, are the waves which heat our food in a ………………… oven.

Microwaves are good for ……………… ………………… from one place to another because microwave energy can ……………………. haze, light rain and snow, clouds, and smoke.

Microwaves Microwaves have

wavelengths that can be measured in centimeters!

The longer microwaves, those closer to a foot (~30 cm) in length, are the waves which heat our food in a microwave oven.

Microwaves are good for transmitting because microwave energy can penetrate haze, light rain and snow, clouds, and smoke.

Infra Red Radiation The ………………… that we feel

from sunlight or a fire is infrared radiation.

………………., near infrared waves are not hot at all - in fact you cannot even feel them. These shorter wavelengths are the ones used by your TV's ……………. ……………..

To make infrared pictures like the one above, we can use special cameras. The …………….. areas are the warmest and the …………………….. areas are the coldest.

Infra Red Radiation The heat that we feel from

sunlight, a fire, a radiator or a warm sidewalk is infrared.

Shorter, near infrared waves are not hot at all - in fact you cannot even feel them. These shorter wavelengths are the ones used by your TV's remote control.

To make infrared pictures like the one above, we can use special cameras. The orange areas are the warmest and the white-blue areas are the Hottest.

Visible Light Visible light is made up of the various ..................... of

colored light. The ……… is determined by the frequency of the

light. When electromagnetic radiation of this frequency falls

on our ……………. our brain interprets it as colour.

Visible Light Visible light is made up of the various frequencies

of colored light. The colour is determined by the frequency of the

light. When electromagnetic radiation of this frequency

falls on our retina our brain interprets it as colour.

Longer wavelengths are refracted the LEAST!

Calculate the frequency of green light. = 520 nm

Ultraviolet (UV) light Ultraviolet (UV) light has

………… wavelengths than visible light.

Ultraviolet radiation seems to play an important role in ……… some animals have colours that change in UV light – other animals can detect UV light.

Though these waves are invisible to the human eye, some insects, like …………….., can see them!

Also used for ................... …………….

Ultraviolet (UV) light Ultraviolet (UV) light has

shorter wavelengths than visible light.

Ultraviolet radiation seems to play an important role in nature some animals have colours that change in UV light – other animals can detect UV light.

Though these waves are invisible to the human eye, some insects, like bumblebees, can see them!

Also used for security coding.

X - Rays X-Ray radiation has a high

…………………….. ability and can pass right through our bodies.

X-rays film forms images depending on the ………………….. of the X-rays falling on it.

The ……………….. left by things that the X-rays can't travel through (like bones or metal) form the …………… on medical X-rays.

Over exposure can cause ……….. …………………….

X - Rays X-Ray radiation has a high

penetration ability and can pass right through our bodies.

X-rays film forms images depending on the intensity of the X-rays falling on it.

The shadows left by things that the X-rays can't travel through (like bones or metal) form the images on medical X-rays.

Over exposure can cause tissue damage.

Gamma-rays Gamma-rays have the

…………………… wavelengths and the most energy of any other wave in the electromagnetic spectrum.

These waves are generated by …………………………. and in nuclear explosions.

Gamma-rays can …………. living cells, a fact which medicine uses to its advantage, using gamma-rays to kill …………… cells.

Gamma-rays Gamma-rays have the

smallest wavelengths and the most energy of any other wave in the electromagnetic spectrum.

These waves are generated by radioactive atoms and in nuclear explosions.

Gamma-rays can kill living cells, a fact which medicine uses to its advantage, using gamma-rays to kill cancerous cells.

Electromagnetic Spectrum

Energy of a Light

• Energy of a photon E = ....... Max Planck

• Wave equation = ............• speed of light = ....... (symbol)

.:To calculate the energy of a photon energy of a photon of light with wavelength and speed c:

E =................

Eg, Calculate the energy of a photon of blue light. ( = 450 nm)

Energy of a Light

• Energy of a photon E = hf Max Planck• Wave equation = f x • speed of light = c

To calculate the energy of a photonenergy of a photon of light with wavelength and speed c

.: EE = h(c/ )

h = 6.63 X 10-34 J.s

Eg, Calculate the energy of a photon of blue light.

E = hf

= (6.63x10-34)*(3x108/450x10-9) = 4.4x10-9J

PolarizationThe electric and magnetic

fields in light oscillate in ............... DIRECTIONS.

A Polaroid filter allows the ……………….field through in ………. PLANE only – i.e. the light has been PLANE ……………………….

If a second Polaroid filter is placed at ………. to the first NO LIGHT WILL PASS THROUGH!

PolarizationThe electric and

magnetic fields in light oscillate in ALL DIRECTIONS.

A Polaroid filter allows the ELECTRIC field through in ONE PLANE only – i.e. the light has been PLANE POLARISED.

If a second Polaroid filter is placed at 90o to the first NO LIGHT WILL PASS THROUGH!

Penetrating ability

• Penetrating ability depends on frequency which also determines the ENERGY of the radiation.

• Lower energy vibrations UV, visible & IR are absorbed by many molecules (causing molecules to vibrate) and so do not travel far in most mediums.

• Very low frequencies Radio are not absorbed well and so travel far through low density substances like air.

EM Summary

Radiation Produced Rel. Size Penetration USE

()

()

X

UV

Visible

IR

Micro

Radio

EM SummaryRadiation Produced Rel. Size Penetration USE

() Radioactive decay

() Cathode ray tubes

X High energy

electron collisions

UV Sun / lamps

Visible White Hot objects

IR heat

Micro Magneto

Radio Alternating current