1. Electromagnetic Waves
Chapter 24
Electromagnetic Waves

2. The Nature of Electromagnetic Waves
Benefits of Electromagnetic Waves
Visibility (Every thing we see can be attributed to Electromagnetic Waves)
Satellite Communication
Telecommunication
Remote Control
Microwave Oven
X-Rays
Radio Transmission
Laser Surgery
Aircraft Navigation.

3. The Nature of Electromagnetic Waves
Electromagnetic Wave is a coupled
time varying electric and magnetic fields
that propagate in space.
Two straight wires connected to
the terminals of an AC generator
can create an electromagnetic
wave.
Only the electric wave traveling to the
right is shown here.

4. 24.1 The Nature of Electromagnetic Waves
Faraday – Lenz stated that Time-Varying Magnetic Field generates an Electric Field.
Changing Magnetic Flux induces an EMF which in turn produces a Current, hence an Electric Field.
Maxwell stated that if a time varying magnetic field generates an electric field, then a time varying electric field should generate a magnetic field.
The current used to generate
the electric wave creates a
magnetic field.

5. The Nature of Electromagnetic Waves
This picture shows the wave of the radiation field far from the
antenna. (Similar to oscillating pendulum. Acceleration of charges
Produces a changing electric field)
Frequency of oscillating charge is frequency of electromagnetic wave.
The speed of an electromagnetic wave in a vacuum is:

6. The Energy Carried by Electromagnetic Waves
The total energy density carried by an electromagnetic
wave
Energy in an electromagnetic wave is partly carried by the electric field and partly by the magnetic field.
Represents permittivity of free space.
Represents permeability of free.

7. The Energy Carried by Electromagnetic Waves
Properties of Electromagnetic Waves
1. Velocity of Electromagnetic Wave in free space or vacuum is a constant.
2. No material or medium is necessary for propagation.
3. Propagates in the presence of material medium.
4. Electromagnetic waves carry energy and momentum.
5. Electromagnetic waves exert pressure known as Radiation Pressure.

8. The Electromagnetic Spectrum
Like all waves, electromagnetic waves have a wavelength and
frequency, related by:

9. The Electromagnetic Spectrum
Radio
Micro
Infra Red
Visible Light
Ultraviolet
X-Rays
Gamma Ray
Like all waves, electromagnetic waves have a wavelength and
frequency, related by:

10. The Electromagnetic Spectrum
Radio
Micro
Infra Red
Visible Light
Ultraviolet
X-Rays
Gamma Ray
Minimum Frequency
Maximum Wavelength
Maximum Frequency
Minimum Wavelength

11. The Nature of Electromagnetic Waves
Application of Electromagnetic Waves
Radiowaves (produced by accelerated motion of charges in conducting wires)
Used in radio and television communication.
A radio wave can be detected with a receiving antenna wire
that is parallel to the electric field.

12. The Nature of Electromagnetic Waves
With a receiving antenna in the form of a loop, the magnetic
field of a radio wave can be detected.

13. The Nature of Electromagnetic Waves
Bands of Radio Waves
AM (Amplitude Modulated): 550 kHz to 1710 kHz
SW (Short Wave): Up to 54 MHz
TV Wave: 54 MHz to 890 Mhz
FM (Frequency Modulated): 88 MHz to 108 MHz
UHF (Ultra High Frequency)

14. The Energy Carried by Electromagnetic Waves
2. Microwaves: Short Wavelength Radio Waves
Produced by Special Vacuum Tubes
Used in Microwave Ovens and RADAR Systems
Microwave is absorbed by water fats and sugars.
RADAR Systems: Air Traffic Control, Speed Detection, etc…
Electromagnetic waves, like water waves, carry energy.

15. The Energy Carried by Electromagnetic Waves
3. Infra Red Waves (Heat Waves):
Infra Red Lamps, Infra Red Camera, LED Lamps (Remote Control)
Green House Gas Effect : Sun Rays bounce off earth and get
trapped by CO2, CH4 leading to global warming)
4. Light Waves (Red, Orange, Yellow, Green, Blue, Indigo, Violet)
5. Ultraviolet Waves (Produced by Very Hot Bodies, example Sun). Ozone Layer protects us from UV Waves.
6. X-Ray (Produced by bombarding metal target by high energy electrons). Penetrates Flesh Low density but cannot penetrate bone (high density)
7. Gamma Rays (Produced by Nuclear Reactions and emitted by
Radioactive materials).
Used in cancer treatment.

16. POLARIZED ELECTROMAGNETIC WAVES
Polarization
POLARIZED ELECTROMAGNETIC WAVES
Polarization is the process of transforming unpolarized light into polarized light
Polarization is observed only in transverse waves
Unpolarized Wave: Wave vibrates in multiple planes. The wave vibration keeps changing but it is always perpendicular to the direction of wave travel.
Polarized wave: Wave vibration is confined to a specific plane.
Polarization is done by scattering, reflection and refraction and also by use of polaroids.
Polaroids are materials consisting of long chain molecules alighed in a particular direction.
Intensity of light is lower for polarized light.

17. POLARIZED ELECTROMAGNETIC WAVES
Polarization
POLARIZED ELECTROMAGNETIC WAVES
Linearly polarized wave
on a rope.

18. In polarized light, the electric field
Polarization
In polarized light, the electric field
fluctuates along a single direction.

19. Polarized light may be produced from unpolarized light with
Polarization
Polarized light may be produced from unpolarized light with
the aid of polarizing material.

20. MALUS’ LAW intensity before intensity after analyzer analyzer
Polarization
MALUS’ LAW
intensity before
analyzer
intensity after
analyzer

21. Example 7 Using Polarizers and Analyzers
Polarization
Example 7 Using Polarizers and Analyzers
What value of θ should be used so the average intensity of the polarized
light reaching the photocell is one-tenth the average intensity of the
unpolarized light?

22. Polarization

23. When Polaroid sunglasses are crossed, the intensity of the
Polarization
When Polaroid sunglasses are
crossed, the intensity of the
transmitted light is reduced to
zero.