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NCERT Exemplar · Class 12 · Physics

Chapter 8: Electromagnetic Waves

Practice each question, then open the answer or worked solution.

Questions

32 questions
Q8.31Written answer

A plane EM wave travelling in vacuum along z-direction is given by
Exemplar Solutions Class 12 Physics Chapter 8 - 29

a) evaluate
Exemplar Solutions Class 12 Physics Chapter 8 - 30 over the rectangular loop 1234 shown in the figure

Exemplar Solutions Class 12 Physics Chapter 8 - 31

b) evaluate
Exemplar Solutions Class 12 Physics Chapter 8 - 32over the surface bounded by loop 1234

c) use equation
Exemplar Solutions Class 12 Physics Chapter 8 - 32 to prove E0/B0 = c

d) by using a similar process and the equation
Exemplar Solutions Class 12 Physics Chapter 8 - 33, prove that
Exemplar Solutions Class 12 Physics Chapter 8 - 34

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Worked solution

a)

Exemplar Solutions Class 12 Physics Chapter 8 - 35

Exemplar Solutions Class 12 Physics Chapter 8 - 36

b)

Exemplar Solutions Class 12 Physics Chapter 8 - 37

Exemplar Solutions Class 12 Physics Chapter 8 - 38

c) Substituting the above equations in the following equation we get

Exemplar Solutions Class 12 Physics Chapter 8 - 39

E0/B0 = 0

d)

Exemplar Solutions Class 12 Physics Chapter 8 - 40

We get c = 1/√μ0ε0

Q8.32Written answer

A plane EM wave travelling along z-direction is described by
Exemplar Solutions Class 12 Physics Chapter 8 - 41 Show that,

i) the average energy density of the wave is given by
Exemplar Solutions Class 12 Physics Chapter 8 - 42

ii) the time-averaged intensity of the wave is given by
Exemplar Solutions Class 12 Physics Chapter 8 - 43

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Worked solution

i) The energy density due to electric field E is

uE = 1/2 ε0E2

The energy density due to magnetic field B is

uB = 1/2 B2/μ0

The average energy density of the wave is given by:

Exemplar Solutions Class 12 Physics Chapter 8 - 44

ii) We know that c=1/√μ0ε0

The time-averaged intensity of the wave is given as

Exemplar Solutions Class 12 Physics Chapter 8 - 45

Electromagnetic waves are also called waves which occur in the electromagnetic field containing powerful electromagnetic radiant energy. Electromagnetic radiation is the medium where the waves exist and can traverse through space, moving at the speed of light. Some of the different types of electromagnetic waves are

  1. Radio waves
  2. Gamma rays
  3. X-rays
  4. Microwaves
  5. Ultraviolet rays

Check out the NCERT Exemplar Class 12 Physics Chapter 8 Electromagnetic waves, available in PDF format below.