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NEETPhysicsElectromagnetic Waves

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): The momentum transferred to a completely absorbing surface of area A exposed to normally incident light of intensity I for time t is IAt c . Reason (R): The total energy incident on the surface is IAt and the momentum transferred by the absorbed electromagnetic wave is its energy divided by the spe

Options

  1. ABoth Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
  2. BBoth Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
  3. CAssertion (A) is true but Reason (R) is false.
  4. DAssertion (A) is false but Reason (R) is true.

Correct answer

A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

Step-by-step solution

Intensity I is defined as the energy incident per unit area per unit time. Therefore, the total energy E incident on a surface of area A in time t is given by E = IAt . For a completely absorbing surface, the entire incident energy is absorbed. The momentum p transferred by an electromagnetic wave is related to its energy E by the relation p = E c , where c is the speed of light. Substituting the expression for energy, we get p = IAt c . Thus, both Assertion (A) and Reason (R) are true, and Reason (R) provides the

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