Physics · Interference: Young's double-slit experiment and expression for fringe width, coherent sources and sustained interference of light
Two coherent monochromatic light beams of intensities and are superposed. The ma
Two coherent monochromatic light beams of intensities \( I \) and \( 4 I \) are superposed. The maximum and minimum possible intensities in the resulting beam are:
- A. \( 5 I \) and \( I \)
- B. \( 5 I \) and \( 3 I \)
- C. \( 9 I \) and \( I \)
- D. \( 9 I \) and \( 3 I \)
Step-by-step solution
For coherent waves, the resultant intensity I_res = I1 + I2 + 2√(I1 I2) cosφ. Maximum when cosφ = 1: I_max = (√I1 + √I2)^2 = (√I + √(4I))^2 = (√I + 2√I)^2 = (3√I)^2 = 9I. Minimum when cosφ = -1: I_min = (√I1 - √I2)^2 = (√I - 2√I)^2 = (-√I)^2 = I.
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