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Karnataka Board PUCPUC Science 2nd PUC Class 12

An electromagnetic wave travelling along z-axis is given as: E = E0 cos (kz – ωt.). Choose the correct options from the following; The associated magnetic field is given as ωB=1ck^×E=1ω(k^×E). - Physics

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Question

An electromagnetic wave travelling along z-axis is given as: E = E0 cos (kz – ωt.). Choose the correct options from the following;

  1. The associated magnetic field is given as `B = 1/c hatk xx E = 1/ω (hatk xx E)`.
  2. The electromagnetic field can be written in terms of the associated magnetic field as `E = c(B xx hatk)`.
  3. `hatk.E = 0, hatk.B` = 0.
  4. `hatk xx E = 0, hatk xx B` = 0.

Options

  • a, b and c

  • a, c and d

  • b, c and d

  • b and d

MCQ
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Solution

a, b and c

Explanation:

a. The direction of propagation of an electromagnetic wave is always along the direction of vector product `vecE xx vecB`. Refer to figure.


`vecB = Bhatj = B(hatk xx hati) = E/c (hatk xx hati)`

= `1/c [k xx Ehati] = 1/c [hatk xx vecE]`  .....`("as"  E/B = c)`

b. `vecE = Ehati = cB(hatj xx hatk) = c(Bhatj xx hatk) = c(vecB xx hatk)`

c. `hatk * vecE = hatk * (Ehati)` = 0, `veck * vecB = hatk * (Bhatj)` = 0

d. `hatk xx vecE = hatk xx (Ehati) = E(hatk xx hati) = Ehatj` and `hatk xx vecB = hatk xx (Bhatj) = B(hatk xx hatj) = - Bhati`

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Chapter 8: Electromagnetic Waves - MCQ I [Page 49]

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NCERT Exemplar Physics [English] Class 12
Chapter 8 Electromagnetic Waves
MCQ I | Q 8.09 | Page 49

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