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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: Light is a transverse wave but not an electromagnetic wave.
Reason: Maxwell showed that speed of electromagnetic waves is related to the permittivity of the medium through which it travels.
✓

Answer

  1. A is false and R is also false.
Explanation:

The speed of em waves in free space is given by $\text{c}=\frac{1}{\sqrt{\mu_0\in_0}}.$

Where $\mu_0=4\pi\times10^{-7}\text{N}\frac{\text{s}^2}{\text{C}^2}$ is penneability constant of vacuum and $\in_0=8.85419\times10^{-12}\frac{\text{C}^2}{\text{N}}\text{m}^2$ is the permittivity of free space. After substituting these value, the value of $\text{c}=\big(2.99792\times10^8\frac{\text{m}^2}{\text{s}}\big)$ which is same as the speed of light in vacuum. From this it is concluded that light is an electromagnetic wave.

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