Q. Two non-coherent sources emit light beams of intensities $I$ and 4$I$ . The maximum and minimum intensities in the resulting beam are
A) $9I\ and\ I$
B) 9$I$ and 3$I$
C) 5$I\ $and $I$
D) 5$I\ $and 3$I$
Explanation
(d) When two coherent light beams of intensities $I_{1}\ and\ I_{2}$ superimpose, then maximum intensity is $\left( \sqrt{I_{1}} - \sqrt{I_{2}} \right)^{2}$ and minimum intensity is$\left( \sqrt{I_{1}} - \sqrt{I_{2}} \right)^{2}$. But when two incoherent light beams of intensities $I_{1}\ and\ I_{2}$ superimpose, then maximum intensity is $\left( I_{1} + I_{2} \right)$ and minimum intensity is$\left( I_{1} - I_{2} \right)$.
$\therefore\ \ \ \ \ I_{\max} = 5I,\ I_{\min} = 3I$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.