NEET
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- NEET
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- Physics
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- Wave Optics
NEET · Physics · Wave Optics
Consider the following four optical arrangements intended to...
Consider the following four optical arrangements intended to produce an interference pattern on a screen:
(I) Two independent sodium lamps of the same wattage placed close to each other.
(II) Two narrow slits illuminated by a single monochromatic laser beam.
(III) Two independent laser pointers emitting light of the exact same wavelength.
(IV) Light from a single narrow slit and its reflection from a plane mirror.
How many of the above arrangements will successfully produce a sustained interference pattern?
(I) Two independent sodium lamps of the same wattage placed close to each other.
(II) Two narrow slits illuminated by a single monochromatic laser beam.
(III) Two independent laser pointers emitting light of the exact same wavelength.
(IV) Light from a single narrow slit and its reflection from a plane mirror.
How many of the above arrangements will successfully produce a sustained interference pattern?
Options
- AOnly one
- BOnly three
- COnly two
- DAll four
Correct answer
C. Only two
Step-by-step solution
For a sustained interference pattern to be observed, the sources of light must be coherent, meaning they must maintain a constant phase difference with respect to time.
(I) Two independent sodium lamps are incoherent sources because light is emitted by independent atoms randomly, leading to a rapidly changing phase difference. They will not produce a sustained pattern.
(II) Two narrow slits illuminated by a single laser beam act as coherent sources because they are derived from the same original wavefront (Young's double-slit setup). They will produce a sustained pattern.
(III) Two independent laser pointers, despite being highly monochromatic, are still independent sources. Their relative phase will drift randomly, so they cannot produce a sustained interference pattern.
(IV) Light from a single slit and its reflection from a plane mirror act as two coherent sources because the reflected virtual source is derived from the real source (Lloyd's mirror setup). They will produce a sustained pattern.
Thus, only two arrangements (II and IV) will produce a sustained interference pattern.
Answer: Only two
(I) Two independent sodium lamps are incoherent sources because light is emitted by independent atoms randomly, leading to a rapidly changing phase difference. They will not produce a sustained pattern.
(II) Two narrow slits illuminated by a single laser beam act as coherent sources because they are derived from the same original wavefront (Young's double-slit setup). They will produce a sustained pattern.
(III) Two independent laser pointers, despite being highly monochromatic, are still independent sources. Their relative phase will drift randomly, so they cannot produce a sustained interference pattern.
(IV) Light from a single slit and its reflection from a plane mirror act as two coherent sources because the reflected virtual source is derived from the real source (Lloyd's mirror setup). They will produce a sustained pattern.
Thus, only two arrangements (II and IV) will produce a sustained interference pattern.
Answer: Only two