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 .