Saturday 14 July 2012

ELECTROMAGNETIC WAVES



ELECTROMAGNETIC WAVES


The oscillating electric & magnetic field which regenerate each other & propagate through space with speed of light are known as electromagnetic waves.

Properties of electromagnetic waves


1.      E.M waves require no material, medium for propagation .
2.      E.M waves are transverse in nature .
3.      Speed of E.M wave is different in different media & is given by : ν=1/√μϵ . It is maximum in air/vacuum & equal to
     c = 1/√μ0ϵ0 =3 x 108 m/s
4.      Ratio of electric field to magnetic field gives speed .
                     C=E0/B0

ELECTROMAGNETIC SPECTRUM

The orderly distribution of different type of E.M. waves according to their specific characteristic like frequency wavelength etc. is called electromagnetic spectrum .


TYPES OF E.M. WAVES

1.      Radio waves
2.      Micro waves
3.      Infrared waves
4.      Visible rays
5.      Ultraviolet rays
6.      X rays
7.      Gama rays.
 In ascending order of frequency for different type of waves :                                                        
Radio waves <Micro waves < Infrared waves < visible rays< ultraviolet rays < X rays < Gama rays .
            

E.M.WAVE AT A GLANCE

Types of E.M. waves

Wavelength range
Frequency range

Source

Way of detection
Applications/ effects

Radio waves

Greater than 10cm
500kHz to 1000mHz
Rapid acceleration & deacceleration of electrons
Reciver aerial
Radio & TV communication

Micro waves

1mm to10 cm
109to 1012Hz
Klystron valve Magnetron valve
Point contact diodes
Used in radar system
Micro wave oven
Infrared waves
700nm to 1mm
1012 to 4x1014Hz
Vibration of atoms & moleculs
Thermoriles
Bolometers
Infraphotographic film
Cause heating effect
Physical therapy
Remote switches 
Visible rays
400nmto 700nm
4x1014 to7x10 14Hz
Electrons in atoms emit light when they move from one energy level to lower energy level
The eye, photo cell &
Photographic films
To see objects
To convert in electric energy
To take photographs optical signal
Ultraviolet waves
6x10-10m to 400nm
7x1014to5x1017Hz
Inner shell electron in atom moving from one energy level to lower energy level
Photocell Photographic films
LASIK eye surgery &
To kill germs

X rays
10-3nm to1nm
3x1016to 3x1020Hz
X ray tube or innershell electron
Photographic film Geiger tubes Ionisation chamber
Diagnostic measure,
Treatment of cancer &
To locate the fracture of bones
Gama rays
Less than 10-4to10-10m
Greater than 3x1020or1019Hz
Radioactive decay of nucleus
Photographic film Geiger tubes Ionisation chamber
To destroy cancer cells
Experimental study

  “  Electromagnetic wave”2
1-State any four properties of electromagnetic waves ?
2-Arrange following  radiation is the descending order of the wavelength  ?
   Gama rays , infrared rays microwaves , yellow light , radio waves .                                                                             
 3-write an expression for speed of electromagnetic waves in free space .                                 
 4-give one use of following .-
a.      infrared rays
b.      gamma rays
c.      microwaves
d.      ultraviolet radiation .
 5-Deduce an expression for the distance which the T.V. signal can directly be received from a T.V. tower of height .
6- By which way the X- rays and  gamma rays  can be produce and detected write one use of  each .                     
7- What oscillate in E.M. Waves? Give four example of E.M. waves .
8.- identify the part of the electromagnetic spectrum which is
a.      Suitable for radar system used in air craft navigation
b.      Which is adjacent to low frequency end of the E.M.       spectrum .
c.      Produced in nuclear reaction
d.      produced by bombarding a metal target by high speed electron
  9- Name the radiation of the electromagnetic spectrum which are used in
1.      War far to look through fog.
2.      Radar of geostationary satellite
3.      studying the structure and properties of atom and molecules
4.      Killing germs.
5.      To take photograph of internal part of human body.
6.      To produce intense heating effect.
    10 – why sky wave are not used in transmission of T.V. signal .Why the transmission of the signal using sky wave is restricted to up to 30 MHz .

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