Electro magnetic radiation
Electro magnetic radiation.
Wave.
Hertz.
Propagation speed of EMR.
Energy of EMR.
The EMR spectrum.
Matter and EMR.
Radio wave.
Radio communication.
Medium wave.
Short wave.
FM radio.
Smart phones.
Bluetooth.
Wi-Fi.
Television.
Radar.
Satellite communication.
Infrared.
Green house effect.
Visible light.
Ultra violet.
X-rays.
Gamma ray.
Technology using EMR.
Electro magnetic radiation.
What is common to Radio, Light, T V, Remote control, Microwave, X-ray, Radar, Satellites,
Smart phones, and Nuclear Reactions ?
All of them, are in one way or other, related to Electro Magnetic Radiation.
Electro Magnetic Radiation, or EMR, is a wave,
of electric and magnetic fields.
We find natural EMR, all around us.
The most common, and ubiquitous Electro Magnetic Radiation is sunlight.
Light is one form of EMR.
There are many other forms of Electro Magnetic Radiation.
We make use of EMR, in many man made devices.
All EMR have some fundamental common properties,
and some variable properties.
The variable properties, are related to the wave characteristics, of EMR.
Wave.
Many phenomena in nature, propagates as waves.
Everything in the electromagnetic spectrum, propagate as waves.
It is worth knowing some basic things, about waves, which is common to all these phenomena.
Let us imagine an object moving forward.
While moving forward, the object simultaneously rises and falls, like a wave.
This kind of movement of the object, is a wave form.
Another way to imagine waves, is to imagine side by side, exactly similar hills.
The hills have a peak, which is the highest point.
The hills have a valley, which is the lowest point.
We can plot a wave form, on a graph sheet.
Let the X axis, cut the wave, exactly in half.
The graph will look like a hill, on the top or positive side, of the X axis,
followed by an inverted hill on the negative side, of the X axis.
This pattern will keep repeating.
That is the wave keeps rising, falling, rising, falling, and so on.
We say the wave, has a rhythmic repeating pattern.
A wave can have many forms.
The forms define the shape of the wave.
A sine wave is one such form.
A sine wave is a mathematical curve,
that describes a smooth, periodic, repetitive oscillation.
A sine wave, is also called as a sinusoidal wave form.
In this module, we will discuss the sine wave,
Which is the most commonly found wave, in natural phenomena.
One wave will have both, a rising part, and a falling part.
The wave rises, from the X axis, to its peak,
falls till it intersects, the X axis,
falls below the X axis, till the valley bottom,
and rises again, to intersect the Y axis.
This whole pattern, is called, one oscillation of the wave.
The height of the highest point, of the wave, from the x axis, is called the amplitude.
The amplitude is also the distance, of the lowest point, from the x axis.
Amplitude is represented by the character, ‘A’.
The difference, between the starting and the ending points, is the wavelength.
The distance between the peaks, is also the wave length.
The distance between the valley bottoms, is also the wavelength.
Wavelength is a standard property of a wave.
The unit of the wavelength, is length,
it is represented with a symbol, called lambda.
When the wave is moving,
it will cross the same point, multiple times.
The rate at which the wave is moving, is the velocity of the wave.
The wave will cross the same point, multiple times, in one second.
This is called, the frequency of the wave.
The number of oscillations of the wave, in one second, is called the frequency of the wave.
Frequency is represented by the character, ‘f’.
For example, if the wave crosses the same point, 20 times in a second,
it has a frequency, of 20 oscillations per second.
To summarise,
a wave has a wave form,
it has a velocity,
it has a wavelength,
and it has a frequency.
Hertz.
Hertz is the unit, by which the frequency, of a wave, is defined.
One oscillation per second, is defined as a hertz.
A wave, which has 20 oscillations per second, is said to have a frequency, of 20 hertz.
A wave which has 20,000 oscillations per second, is said to have a frequency of 20,000 hertz.
Propagation speed of EMR.
All EMR propagate at the speed of light.
Light itself is a form of EMR.
The speed of propagation of EMR, is about 300 thousand Kilometers per second.
Sunlight for example, travels at this speed, from the Sun to the Earth.
It takes about 7 min, to reach the Earth.
It is interesting to know, though we are discussing many types of EMR,
all of them propagate, at the same speed of 300 thousand Kilometres per second.
Energy of EMR.
We can also consider, the propagation of EMR, as the propagation of particles.
The basic particle, in all EMR’s, is the photon.
The photon has an energy, associated with it.
This energy is proportional to the frequency of the EMR wave.
There is a simple equation to measure this energy.
Energy of the photon is equal to h multiplied by f.
f is the frequency of the EMR.
h is the Planck's constant.
The value of h, is about 6.6 multiplied by 10 to the power of minus 34 joules.
This is a very small unit of energy.
EMR energy is measured in electron volts.
The symbol for electron volt is e V.
A electron volt is the energy, required to move an electron,
across a electrical potential difference of 1 volt.
An electron volt is about 1.6 multiplied by 10 to the power of minus 19 joules.
High frequency EMR’s have high energy.
Example X-rays.
Low frequency EMR’s have low energy.
Example Radio waves.
The EMR spectrum.
EMR comprises of a continuous stream, of waves.
EMR Spectrum, is a collective term, for all the EMR waves.
The Spectrum comprises of waves from very low frequencies to very high frequencies.
Frequency is inversely proportional to wave length.
The same spectrum, comprises of waves, from very long wave length, to very short wave length.
The energy of EMR, is proportional to the frequency.
Higher the frequency, higher the energy of EMR.
The EMR Spectrum, comprises of waves from very low energy to very high energy.
The EMR Spectrum is a continuum.
For practical convenience, we classify the spectrum, into different groups of frequencies.
Each group is a category.
Each category is specially suited for some type of applications.
For example, Radio waves are suited for Radio communications.
Following is a broad classification, of the continuous EMR spectrum.
Radio waves.
Radio waves have a frequency, ranging from 3 hertz ,to 300 Gigahertz.
Wave length ranges from 100,000 km to 1 millimeter.
Energy of radio waves ranges from 12.4 femto electron volts to 1.24 million electron volts.
The frequency range, from 300 Megahertz to 300 Gigahertz, is also called as Micro wave.
Infra red waves.
Infra red waves have a frequency, ranging from 300 Gigahertz to 400 Terahertz.
Wave length ranges from 1 millimeter to 700 Nanometer.
Energy of Infra red waves ranges from 1.24 micro electron volts to 1.7 electron volts.
Visible Light.
Visible Light has a frequency, ranging from 400 Terahertz to 770 Terahertz.
Wave length ranges from 750 Nanometer to 390 Nanometer.
Energy of Visible light ranges from 1.7 electron volts to 3.2 electron volts.
Ultra Violet waves.
Ultra Violet waves have a frequency, ranging from 750 Terahertz to 30, Petahertz.
Wave length ranges from 400 Nanometers to 10 Nanometers.
Energy of Ultra Violet waves ranges from 3 electron volts to 124 electron volts.
X-rays.
X-rays have a frequency, ranging from 30 Petahertz to 30 Exahertz.
Wave length ranges from 10 Nanometers to .01 Nanometer.
Energy of X-rays ranges from 124 electron volts to 124 Kilo electron volts.
Gamma rays.
Gamma rays have frequencies, more than 15 Exahertz.
Have Wave length less than .02 Nanometers.
Energy of Gamma rays, is more than 62.1 Kilo electron volts.
Matter and EMR.
When EMR interacts with matter, one or more of the following things can happen.
Refraction.
The path of the EMR may get deflected.
Reflection.
The EMR might get reflected back, to the source.
Absorption.
The EMR might get absorbed by the receiving matter.
Emission.
The EMR might result in emission of some other radiation.
Radio waves.
Radio waves have a frequency, ranging from 3 hertz ,to 300 Gigahertz.
Wave length ranges from 100,000 km to 1 millimeter.
Energy of radio waves ranges from 12.4 femto electron volts to 1.24 million electron volts.
The frequency range, from 300 Megahertz to 300 Gigahertz, is also called as Micro wave.
A large segment of the EMR, comprises of Radio waves.
As the name implies, Radio waves are mostly used for communication.
It is important to remember, that the spectrum of Radio waves,
in fact all of EMR,
is a continuous range of waves,
with a frequency and wave length.
Radio waves are usually grouped, in chunks of frequency ranges.
These chunks of frequency ranges are given a name,
but usually they are referred to by an abbreviation.
For example, we might have heard of V H F, which stands for Very high frequency.
These groupings are more for our convenience.
Natural EMR, does not have boundaries.
It is a continuous spectrum of waves, from very low frequencies to very high frequencies.
The grouping is convenient, because each group of frequencies,
have some special properties, which are used for specific applications.
Some of the common frequency groups of Radio waves are,
ULF, Ultra Low Frequency.
VLF, Very Low Frequency.
LF, Low Frequency.
MF, Medium Frequency.
HF, High Frequency.
VHF, Very High Frequency.
UHF, Ultra High Frequency.
SHF, Super High Frequency.
EHF, Extremely High Frequency.
The higher frequency groups, are collectively, also known as Micro waves.
Radio communication.
One of the significant discoveries of the 20th century, is Radio communication.
Before that, we could not even imagine, that we could communicate to another person,
through thin air.
Today, Radio communication is pervaded, so many aspects of our life,
that we cannot imagine a world without it.
The Radio is the earliest, and the simplest Radio communication device.
The basic principal in Radio communication is,
a sound signal is encoded in a Radio wave.
A transmitting station, encodes a sound signal, in the Radio wave.
This is called modulation.
The transmitting station, transmits the Radio wave, via a powerful antenna.
This radio wave propagates in all directions.
It is important to note that a transmitting station,
transmits the signal at a very specific frequency.
Two Radio stations, never transmit, at the same frequency.
If they do, the signal will interfere, with each other.
A Radio receiver has an antenna.
The antenna picks up all the Radio signals, near it.
This might be coming from many transmitting stations.
A tuner selects a particular frequency.
Depending on which station we wish to listen,
We can tune in to that station’s frequency.
The signal is amplified.
A demodulator, extracts the sound signal, from the radio wave.
We get to listen to the sound signals, through the speakers.
Radio communication has become very sophisticated.
Today, We have a very wide range, of Radio communication devices.
But the basic principles, of Radio communication remain the same.
Medium wave.
A Medium wave is a range of medium frequency, Radio waves.
The frequency range is from 300 hertz to about 1.6 Megahertz.
Usually medium wave transmissions, are amplitude modulated.
This means, that the amplitude of the Radio wave, is modulated,
according to the sound wave.
Amplitude modulation is called as AM.
Medium wave communication is usually used for shorter distances.
A local Radio station of a city, will transmit in medium wave.
The transmission will cover only the city.
Short wave.
Short waves have a frequency of about 1.6 to 30 Megahertz.
Short waves have a special characteristic property.
They get reflected by the ionosphere.
This way, Short waves are able to travel around the globe.
So, a transmitting station, which wants to transmit around the globe,
would use short wave.
This way with the short wave receiver, we can listen to Radio stations, around the world.
FM radio.
FM Radio signals are frequency modulated.
This means, the frequency of the Radio wave, is modulated,
to encode the sound wave.
FM Radio uses very high frequency, or VHF for broadcasting.
The frequency range, of FM, is usually 87.5 to 108 Megahertz.
FM broadcast uses Hi Fi or High Fidelity sound.
This enhances the quality of sound.
Smart phones.
Smart phones are also known as Mobile phones, or Cell phones.
Earlier all telephones in the world, were connected by cable.
But, the mobile telephones, allowed the user,
to carry the telephone, wherever they went.
This concept became very popular.
Mobile telephones receive the wireless signals through a cellular tower.
It uses a network of cellular towers.
The cellular towers transmit signals among themselves.
This allows a person, to talk to another person anywhere in the world.
1980’s was the beginning of the mobile phone.
These were bulky devices.
We now call them 1G phones.
1G phones used analog technology.
The next generation 2G phones, was based on GSM technology.
GSM technology was introduced in the 1990’s.
GSM stands for Global System for Mobile Communication.
The important difference of 2G was that, it used digital technology.
Mobile devices became smaller and more convenient to carry.
With digital technology, the quality of sound improved.
GSM also allowed for text or SMS messages.
3G technology was introduced after 2001.
This allowed much higher communication speeds.
3G phones could be used for many more functionalities.
Camera equipped phones could instantly transmit pictures.
This was called MMS, or Multi Media Messaging Service.
It enabled video calls.
It enabled mobile internet.
This meant, that the internet could be accessed, through the mobile.
This was a very significant development.
Accessed to the internet, dramatically increased the functionality, of the phone.
Many applications were built, making use of the internet.
Phones were now called as smart phones.
Current technology is called 4G.
4G enables for much higher speeds, for mobile communication.
Communication speeds can range from hundred mega bits per second,
to 1 Giga bit per second.
Many more applications are now becoming possible on the smart phone.
Video conferencing, 3D television, Cloud computing etc. has become possible.
The future hold enormous potential, for mobile telephony.
In Radio communication, there is one tower,
which is broadcasting the wireless signals.
Many users, with Radio sets receive the signals.
There is an important difference between this,
and mobile communication.
Mobile communication is typically, point to point communication.
One specific person, communicates with another specific person.
A Radio receiver, is not uniquely identified.
In contrast, every mobile phone is uniquely identified.
This is made possible, by a unique electronic card.
This is called as the SIM card.
SIM stands for Subscriber Identity Module.
Each SIM card has a unique global identity.
When the SIM card is installed in a mobile telephone,
the mobile becomes uniquely identifiable.
This way the mobile, picks up only those Radio signals,
which are meant for it, ignoring all other signals, which are going around.
Bluetooth.
Bluetooth is a wireless technology,
used for exchanging data, over short distances.
Usually this distance is about 10 m.
Bluetooth uses ultra high frequency,
or UHF Radio waves.
The frequency range is 2.4 to 2.8 Gigahertz.
The most familiar use of Bluetooth,
is the wireless communication between the mobile phone and the headset.
The mouse, keyboard, and printer, can also be connected by Bluetooth, to the computer.
Bluetooth technology is also used in other smart devices.
Wi-Fi.
WiFi is a local area wireless technology.
It allows an electronic device to connect to the internet.
It uses a frequency range of 2.4 to 5 Gigahertz.
A WiFi transmitter is located in a convenient place,
at home, in the office, or in a public place.
Usually it has a range of 20 m and more.
Many electronic devices like computers laptops, video game consoles,
audio players, and tablet computers, can connect to this transmitter.
In this way Internet becomes available to all these devices.
A public place like an airport or an a hotel, which has WiFi is called a hotspot.
This makes it convenient to connect to the internet, even while travelling.
Television.
A television signal has got two components.
An audio component, and a video component.
TV signals are encoded in Radio waves.
TV signals can be broadcast in many ways.
A TV station can broadcast the signals, in the air.
These signals are received by TV, through an antenna.
The signals can be transmitted, via a fibre optic cable.
The cable distributor, could receive the signals, from a satellite.
The fibre optic cables are laid out, to reach individual homes.
A Cable receiver, receives the signals.
The signals can also be transmitted, from a satellite.
The satellite signals, can be directly received, in a home.
A satellite dish antenna, is used for this.
The dish antenna will be installed, so as to point to the satellite.
TV signals can also be transmitted, through the internet.
These signals can be received, by a computer, or a smart phone.
Depending on the media used for transmission,
different ranges of frequency, of Radio waves are used.
Though we have used TV signals as an example,
data, telephone and other signals, can be transmitted, in the same way.
A TV set receives the signal, from one of these sources.
Each TV channel, transmits the TV signal, in a unique frequency.
The TV receiver has a tuner, which can tune into a particular frequency.
The concept is very similar to a Radio receiver.
The audio signal is decoded, and heard through the speakers.
The video signal is decoded, and viewed through the display device.
The display device, is typically a LCD, or a L E D screen.
LCD stands for Liquid Crystal Display.
L E D stands for Light Emitting Diode.
TV has become a common, widely used entertainment device.
Radio waves play a significant part, in TV communication.
Radar.
Radar stands for RAdio Detection And Ranging.
It works with the principle, that Radio waves can be reflected by objects.
One of the common uses of Radar, is Aircraft navigation.
A base station, with a rotating antenna, transmits Radio Pulses.
Radio waves, in the micro wave range, are used for this purpose.
These waves reflect from the Aircraft, and come back to the base station.
From the time lapse, taken from transmission to receiving the Radio wave,
we can determine, the distance of the Aircraft.
We can also determine the altitude, direction, and speed.
This can be used by air traffic controllers, to guide the Aircraft.
Radar is used by Air Defence system, anti missiles systems,
and marine Radar.
Meteorologists use Radar, for weather forecasting.
The police force use Radar guns to monitor vehicle speeds.
Satellite communication.
Satellites are sophisticated man made devices, which orbit the Earth.
Different kinds of orbits are possible.
Leo satellites have Low Earth Orbit.
Polar satellites, orbit around the poles.
Geo synchronous satellites are of special interest to communication.
They have an orbit, which is synchronised, with the Earth’s rotation.
That is the angular velocity of the satellite, is the same that of Earth.
This makes it appear, at the satellite is in a fixed position,
relative to a physical location on Earth.
This is why they are called Geo synchronous satellites.
The advantage of these satellites is that,
they can continuously transmit signals, to a wide geographical location.
They are like having a transmitter, in the sky.
Because of the height of the satellite, which is about 36000 Km,
the signals from the satellite, can reach a large geographical area.
In fact a network of 3 to 4 satellites, can cover the whole globe.
Another advantage of satellites is, the Radio signals can reach places,
where cables cannot reach.
Signals from satellites can reach ships, aircraft, trains, and cars.
In fact it can reach a hand held satellite phone, even on top of Mount Everest.
A large number of man made satellites, are now orbiting the Earth.
Satellites perform a wide variety of functions, which are very beneficial to mankind.
Some uses of satellite are -
Meteorology.
This application monitors the weather condition through out the globe.
This data is used for weather forecasting.
Navigation.
In early times people travelling by ship, used to navigate,
by tracking the position of stars.
Now ships use satellites, to pin point their exact location.
Aircraft can also use satellites for navigation.
Telephony.
Long distance telephone calls can be routed via satellites.
If you wish to call someone on the other side of the globe,
the signal is transmitted to a satellite, which will transmit it,
to the required location.
Mobile transmission towers, can connect to satellites.
This way mobile phone signals can reach from any part of the globe,
to any other part of the globe.
Television.
TV broadcasting stations, can transmit their signals, to a satellite.
This is called as uplinking.
The satellite in turn can broadcast the signals, to a vast geographical area.
A home dish antenna can receive these signals.
Technically, with satellites it is possible to receive any TV channel,
in the world.
Internet.
Data of the internet, can be routed via satellites.
In this way broadband internet can be reached to remote locations.
GPS.
GPS stands for Global Positioning System.
GPS helps in navigating on land also.
A vehicle can be fitted with a GPS device.
With the help of satellites the vehicles can be tracked, as it moves.
The maps of the world are now available in electronic form.
With GPS we can navigate from one place to another, using these maps.
These systems are becoming so accurate, that a voice from the GPS device,
exactly tells you when to turn left or right, in most major cities of the world.
Infrared.
Infrared electromagnetic radiation,
has frequency range of 300 Gigahertz to 430 Terahertz.
It is called Infrared, because its wave length, is just above,
the wave length of visible light.
It just means that the Infrared spectrum,
is very close to the spectrum of visible light.
Though we cannot see it, we all feel the Infrared spectrum.
About half the energy we receive from the Sun,
comes in the form of visible light.
The other half comes as Infrared radiation.
We can feel this radiation as heat.
So, Infrared radiation, cannot be seen, but can be felt, as heat.
In fact the warmth we feel, from a fire, is via Infrared radiation.
We can see the flames as visible light,
and feel the warmth as Infrared radiation.
Infrared radiation is also used for some man made applications.
It is used for short range communications.
For example, the TV remote uses Infrared communication.
Most remotes use Infrared waves.
A wireless mouse, can also communicate with the computer,
using Infrared waves.
Optical fibres has revolutionised wired communication technology.
They can communicate large volumes of data, at very high speeds.
Telephone, television communication, etc,
are moving towards Optical fibre communication.
Infrared lasers are used in Optical fibre communication.
Printed sign boards cannot be read by visually impaired people.
These sign boards can transmit their contents, in audio form,
using Infrared rays.
These sign boards can be listened to, by visually impaired people.
This technology is called as R I A S.
It stands for Remote Infrared Audible Signage.
This project is in an experimental stage.
Green house effect.
The Sun is the primary source of heat energy, for the Earth.
A significant portion of this Infrared energy,
is naturally reflected back to space.
Because of this, the Earth does not get as hot, as it otherwise would.
But, since the industrial revolution,
a new disturbing trend is taking place.
Industries are releasing more and more Carbon dioxide,
into the atmosphere.
This carbon dioxide, is accumulating in the atmosphere.
C O 2 is one of the Green house gases.
C O 2 and other Green house gases, re-reflect the infrared radiation,
back to Earth.
This is called a Green house Effect.
This is causing the Earth to warm up, more than normal.
This phenomena is called Global Warming.
If unchecked, Global Warming can be environmentally disastrous.
Countries have informally agreed to reduce emissions,
so as to limit Global Warming, to 2 degree centigrade, by the year 2020.
Visible Light.
A electromagnetic radiation with a wave length of 400 Nanometers,
to 700 Nanometers, is visible to the human eye.
In fact it is the only, electromagnetic radiation, that is visible to us.
This is called the visible spectrum.
The whole of electromagnetic radiation, has wave length,
ranging from one picometer to 1000 million meters.
Visible light with a wave length range of 400 to 700 Nanometers,
occupy a microscopic part, of the entire E M R spectrum.
But, they occupy a very important position in science, and our lives.
Simply because they are visible.
If they were invisible, like the rest of the E M R,
we will not be able to see.
Within the visible spectrum, the seven basic colours,
Violet, Indigo, Blue, Green, Yellow, Orange, and Red,
have a specific frequency.
E M R with wave lengths, just above visible light,
is called Infrared.
E M R with wave lengths, just below visible light,
is called ultra violet radiation.
Ultra violet.
Ultra violet radiation have wave lengths, shorter than visible light.
UV light has a wave length ranging from 100 Nanometers to 310 Nanometers.
UV light is not visible, to the human eye.
But, some birds and insects can see, UV light.
A major portion of the UV light, in sunlight,
is blocked by the Ozone layer, in the atmosphere.
A small percentage reaches the Earth.
The human body, uses UV light, to synthesise vitamin D.
Fair skinned people, sunbathe to get a tan.
This tan is caused by UV light.
Excess exposure to UV light is harmful.
UV lamps are used for disinfection in laboratories.
It is also used to purify water.
Optical storage, is the storage of data,
on a optically readable medium.
CD and DVD drives, use this technology.
They use UV laser, to read the signals, in the disc,
with a high degree of speed and precision.
That is why, CD and DVD drives, have much higher storage capacity.
X-rays.
X-rays have a wave length ranging from .01 to 10 Nanometers.
This corresponds to a frequency range of 30 Petahertz,
to 30 Exahertz,
X-rays have high energy.
The energy is proportional to the frequency of the X-ray.
It ranges from 100 electron volts to 100 Kilo electron volts.
X-rays can traverse, relatively thick objects.
It is used in medical radiography.
The bones in our body, absorb X-rays.
The flesh in our body, lets the X-rays pass through.
That is why, we are able to see the white outlines of bones,
in a X-ray.
A fracture in the bone can be detected in the X-ray.
X-rays can also be used to deduct other anomalies.
Computer tomography is called as CT Scanning.
In CT scan a large series of two dimensional X-rays are taken,
of different sections of the body.
These cross sectional images, are combined, into forming a 3 dimensional image.
CT scans are very useful for certain diagnostic purposes,
like detecting tumours,
CT scans should be done on a need basis, responsibly.
Excessive exposure to X-rays, can be harmful.
X-ray microscopy, is used for high resolution images, of very small objects.
X-ray crystallography, is so precise, that it can determine,
the exact positions of atoms in crystals.
Gamma Ray.
Gamma Rays have very high frequencies.
Typically the frequencies, of Gamma rays are above 10 Exahertz.
Due to the high frequency, Gamma rays have very high energy.
The energy of Gamma rays, is usually above 100 Kilo Volts.
Gamma rays have wave lengths, less than 10 Picometers.
Gamma rays are biologically hazardous.
Gamma rays are released when a nuclear bomb explodes.
This causes extensive damage, and death, to a large number of people.
Gamma rays also occur in nuclear reactors.
Nuclear reactors are designed with very thick protective layers,
of concrete, to prevent leakage of Gamma rays.
Technology using EMR.
Most of the spectrum of EMR, from Radio waves to X-rays,
have been put to use, for various applications, useful to mankind.
We are still inventing new uses for EMR.