chap20 Electromagnetic waves-1 - Copy.ppt

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1. Electromagnetic waves

2. Applications :

3. Applications :

5. = d
dt

6. Electromagnetic waves are made up of electrical
vibrations and magnetic vibrations
The dipole antenna is a
simplified version of
broadcasting antenna used
to transmit audio and video
signals. The amplitude or
frequency of the signal is
modulated to transmit the
information.

7. The figure shows a dipole antenna with M charged positively
and N charged negatively. The electric field produced by
dipole will eventually dissappear at great distances.
When the polarity is reversed, the electric field is in the
opposite direction.

8. Now observe the magnetic field B produced :
The magnetic field is maximum when the current is maximum.
When the polarity is reversed, the magnetic filed is in the
opposite direction.

9. The animation shows the orientation of the electric and
magnetic filed vectors in an electromagnetic waves.
The wave is propagating in the x direction.
Electric field vector is vibrating in the y direction.
Magnetic field vector is vibrating in the z direction.

10. Electromagnetic waves consists of electric field and
magnetic field that oscillates sinusoidally.
Are electromagnetic waves transverse or longitudinal waves?

11. What do you notice about the phase between E and B ?
E and B vectors are always in phase.
The two reach the maximum and minimum vibration values
together.
What do you notice about the frequency of E and B vibrations ?
They have same frequency.

12. Progressive wave equation representing the electric field
and magnetic vibrations in the electromagnetic waves

13. The cross product of E x B always gives the direction of
propagation of the wave

14. Comparison with the mechanical waves

15. In 1865, Maxwell predicted theoretically
that electromagnetive waves propagate
through a vacuum at a speed c, a large
and finite value.
Expression derived from the Maxwell
equation :

16. We find that the theoretical value of c agrees with the speed
of light determined experimentally. This leads scientist to
believe light is a type of electromagnetic waves