ELECTROMAGNETIC WAVES AND THE

ELECTROMAGNETIC SPECTRUM

Electromagnetic Radiation Electromagnetic waves

perpendicular waves combing the electric and magnetic fields.

Electromagnetic waves are produced when an electric charge vibrates or accelerates and can travel through empty space or through matter. 

Electromagnetic Spectrum

Gamma rays X – rays Ultraviolet Visible light Infra-red Microwaves Radio waves

Highest frequencyShortest wavelength

Lowest frequencyLongest wavelength

Electromagnetic Spectrum Diagram Diagram of Electromagnetic Spectrum

(including the relationship between frequency and wavelength).

Speed of Electromagnetic Waves

All electromagnetic waves travel at 3.0 x 108 m/s in a vacuum.

Speed of a wave formula: Speed = Frequency x Wavelength

As the frequency increases, the wavelength decreases.\

Electromagnetic Spectrum Includes the following types of waves

Radio Microwaves Radar Infrared Visible Light Ultraviolet X-Rays Gamma Rays

Electromagnetic Spectrum

………………………………………………

Hence this is the complete EM wave spectrum (the waves below in ascending order of wavelength; descending order of frequency )

Gamma rays

x-rays Ultra-violet ray

Visible light

Infra-red ray

Microwave Radio wave

Highest fShortest λ

Lowest fLongest λ

Gamma raysGamma rays have the shortest wavelengths and highest frequencies in the EM spectrum.It is generated by :

Changes in energy levels in the nucleus

Some radioactive substances and certain nuclear reactions produce gamma rays.

Because of their great penetrating ability, gamma rays can cause serious illness. However when used in controlled conditions, gamma rays is useful in cancer treatment.

Uses of Gamma Rays Kill cancer cells Study the

nucleus in atoms

Gamma Rays Gamma rays are the

highest energy electromagnetic wave.

They usually come from radioactive elements or stars Uses include:

Killing cancer cells Making pictures of the brain Inspection tools in industry

X-rays

X rays is generated by : a) Rapid deleceration of fast moving

electrons b) Changes in energy of innermost orbital

electrons

X-rays are used for :• diagnostic tool in dentistry and medicine.

Doctors and dentists can examine the condition of a person’s bones, the root of this teeth or the state of other inner part of the body.

• Custom officers at airports inspect the content of your luggage using X-rays.

• Industry wise, it is used to find cracks in structures just like cracks in bones.

X-Rays X-Rays have high energy and can

penetrate some material. Used in:

Medicine Industry Transportation

Too much exposure can damage living tissue or even cause cancer.

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 ……….. …………………….

Uses of X-rays Take ‘pictures’ of

bones in the body Study the crystal

structure of crystalline substances

Check for cracks in metal plates

Ultraviolet Waves UV Light that is at a higher frequency and

energy than violet light. UV light can kill micro-organisms. Too much exposure can cause:

Sunburn, Wrinkles, and skin cancer As it damages cell DNA

Ultra-violetThe main source of ultra-violet radiation is sunlight and it is this

radiation which gives rise to suntan and also sunburn.

Ultra-violet radiation is used in hospitals to sterilize the surgical instruments and operating theatres as it kills bacteria and viruses.

UV can be detected by:

a) Photographic plates

b) Photoelectric cell

c) Fluorescence

Uses of Ultraviolet Detect

counterfeit notes Gives the clothes

a ‘glow’ effect in discotheques

Sun-tanning Sterilise medical

equipment

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 LightVisible light is the part of the EM spectrum which can be detected by the human eye.

The visible light has its own spectrum which consist of the 7 colours of light :Red Orange Yellow Green Blue Indigo Violet

An example of visible light is the colourful laser light or the light from a firework.

Some of the uses of light is in optical fibres in medicine and telecommunications.

Visible Light Our eyes detect

electromagnetic energy in a small portion of the electromagnetic spectrum called the visible light region.

The visible light region corresponds the wavelengths and frequencies of red, orange, yellow, green, blue, indigo, and violet light.

Uses of Visible Light Enable us to

see things Photosynthesis

in plants

Infra-red wavesHeat can be transferred through infrared radiation.We often think of infra red as being the same thing as 'heat', because it makes our skin feel warm.

Most of you might have seen infra-red waves in use during the SARS period. (picture on the top right hand corner). It shows a thermo-detector which is placed outside hospitals/airport to identify the warm and cool parts of a person by analyzing infra-red radiation emitted from the person’s body. And through this we can see if someone is having a fever.

Infra red is useful for:- For navigation through fog & haze as it is less easily scattered compared to visible light- Medical treatment : to warm injured muscles/sports injuries

Uses of Infra-red Heating Haze

photography

Infrared image of a human body. Red is hot, blue is cool.

Infrared Waves Infrared waves are heat waves. All objects emit infrared waves because all

objects possess heat. Night vision goggles detect infrared waves and

allow the user to see the movement of objects in the dark.

Many TV remotes use infrared.

MicrowavesOne of their most common uses is in microwave ovens. When you switch on a microwave oven , it gives off electromagnetic waves that bounce around inside the oven, penetrating the food. Water molecules in the food absorb the energy from the microwaves, causing the food to get hot.

Other uses of microwaves: a) Radar communication (as it is not easily

blocked of by buildings/trees)b) Analysis of fine details of molecular and

atomic structurec) Useful demonstration of all wave

properties on macroscopic scaled) Telephone communication (mobile

phones, etc)

Uses of Microwaves Radar

communication Analysis of the

molecular and atomic structure

Telephone communications

Radio wavesRadio waves are the electromagnetic waves

with the longest wavelengths and lowest frequencies

Like all electromagnetic waves, radio waves can travel through a vacuum. However most of the radio waves we receive have traveled through air. Take the radio as an example. The radio converts the electromagnetic waves into the sound that comes out of the radio speakers.

Uses of radio waves:a) Radio and television communication

(to transmit sound and picture information over long distance)

b) Radar & satellite communicationc) Navigation or ships & aircrafts

Uses of Radio Waves Radar

communications TV and radio

broadcasting

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

THANK YOU ……..