99 Percentile Qs Bank for JEE MainPhysicsWave Optics
Two point sources S₁ and S₂ separated by a distance 10 m emit light waves of wavelength 4 m in phase. A circular wire of radius 40 m is placed around the sources as shown in figure, then ( O is the centre of the circle and O S₁=O S₂ )
Options
- Apoints A and B are dark and points C and D are bright
- Bpoints A and B are bright and point C and D are dark
- Cpoints A and C are dark and points B and D are bright
- Dpoints A and C are bright and points B and D are dark
Correct answer
C. points A and C are dark and points B and D are bright
Step-by-step solution
Path difference at point B , x_B=S₁ B-S₂ B=0 and at point D , x_D=S₁ D-S₂ D=0 Phase difference, = 2 (0)=0 So, intensity at points B and D I=I_ ^2( / 2)=I_ So, points B and D are bright. Path difference at point A , x_A=35 m [40-5] But, figure shows x_A= x_C is maximum for given circle. When path difference is maximum, intensity will be minimum. So, points A and C are dark.