CBSE Class 12 · 2016 · All India · EM WavesShort Answer

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How are electromagnetic waves produced? What is the source of energy of these waves? Write the mathematical expressions for the electric and magnetic fields of an electromagnetic wave propagating along the z-axis. Write any two important properties of electromagnetic waves.

Solution

An accelerating (oscillating) charge radiates electromagnetic waves: its oscillation produces coupled, time-varying

E

and

B

that propagate outward.
The energy carried by the wave comes from the external source (the agent) that keeps the charge oscillating.
For propagation along z:

E_{x} = E_{0} sin (k z - ω t), B_{y} = B_{0} sin (k z - ω t)

Two properties: (i) they are transverse and need no material medium, travelling through vacuum at

c = 3 \times 1 0^{8}

m/s; (ii) they carry energy and momentum, with

E_{0} = c B_{0}

E_{x} = E_{0} sin (k z - ω t), B_{y} = B_{0} sin (k z - ω t)

CBSE Class 12 Board · 2016 · All India · Subjective

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CBSE Class 12 · 2016 · All India · EM WavesShort Answer

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