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PRACTICE / Coherence

Average the detector signal over its exposure

Two beams separately give 4 and 9 W/m². During an exposure their relative phase stays at 0° for one quarter of the time and 180° for the other three quarters.

What average intensity does the detector record?

Organize the givens & assumptions
  • I₁ = 4 W/m²
  • I₂ = 9 W/m²
  • Time fractions: 1/4 at 0°, 3/4 at 180°

Same-frequency coherent beams, parallel polarization, same observation medium and unchanged individual detector intensities, unless the prompt explicitly averages phase.

  1. A7 W/m27\ \mathrm{W/m^2}
  2. B13 W/m213\ \mathrm{W/m^2}
  3. C25 W/m225\ \mathrm{W/m^2}
  4. D1 W/m21\ \mathrm{W/m^2}

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