JEE Main 2025 Apr 7 Shift 1, Physics Q2: Interference by Thin Film

JEE Main2025Apr 7, Shift 1Physics

Two plane polarized light waves combine at a certain point whose electric field components are

$E_{1} = E_{0} sin ω t$

$E_{2} = E_{0} sin (ω t + \frac{π}{3})$

Find the amplitude of the resultant wave.

Solution

For two sinusoids of equal amplitude $E_{0}$ with a phase difference $ϕ = π /3$ , the resultant amplitude follows the vector-addition rule:

$E = E_{0}^{2} + E_{0}^{2} + 2 E_{0} \cdot E_{0} cos ϕ$

Substitute $cos (π /3) = 1/2$ :

$E = 2 E_{0}^{2} + 2 E_{0}^{2} \cdot \frac{1}{2} = 3 E_{0}^{2} = 3 E_{0} \approx 1.73 E_{0}$

$∴$ Option (3).

Concept behind this question

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