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Electromagnetic Waves — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsElectromagnetic Waves1 Mark
Question
Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion: In an electromagnetic wave, magnitude of magnetic field vector is much smaller than the magnitude of electric field vector.
Reason: Energy of electromagnetic waves is shared equally by the electric and magnetic fields.
✓

Answer

  1. Both A and R are true but R is not the correct explanation of A.

Explanation:

At every instant the ratio of the magnitudes of the electric field to the magnetic field of an em wave is given by $\frac{\text{E}}{\text{B}}=\text{c}.$

From this equation, the magnitude of electric vector is much greater than the magnitude of magnetic vector. Also electromagnetic waves carry energy which is equally shared by electric and magnetic field.

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