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Multiple choice physics superposition of waves coherence young's double slit experiment interference

For the sustained interference of light, the necessary condition is that the two sources should:

  1. Have constant phase difference

  2. Be narrow

  3. Be close to each other

  4. Of same amplitude
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

To obtain a well defined interference patterns, the intensity at points corresponding to destructive interference must be zero, while intensity at the point corresponding to constructive interference must be maximum. To accomplish this the necessary condition is that the two interference sources must be coherent, that is, they must keep a constant phase difference.

Multiple choice physics superposition of waves coherence young's double slit experiment interference

Interference pattern can be produced by two identical sources. Here the identical sources mean that

  1. their size is same

  2. their wavelength is same

  3. the intensity of light emitted by them is same

  4. the emplitudes of light waves emitted by them are same
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For observing interference the term identical source means that their wavelength are the same ( i.e., they are coherent).

Multiple choice physics superposition of waves coherence young's double slit experiment interference

In Lloyd's single mirror method we have

  1. Both sources virtual

  2. One source virtual and one real

  3. Both sources real

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

By reflection we create a virtual source from real source and light from both of these sources are used to create interference pattern in Lloyd's single mirror method.

Multiple choice physics superposition of waves coherence young's double slit experiment interference

The equations of waves emitted $S _1,S _2,S _3$ and $S _4$ are respectively $y _1=20\sin(100\pi t), y _2=20\sin(200\pi t), y _3=20\cos(100\pi t)$ and $y _4=20\cos(100\pi t)$. The phenomenon of interference will be produced by 

  1. $y _1$ and $y _2$
  2. $y _2$ and $y _3$
  3. $y _1$ and $y _3$

  4. Interference will not possible
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
To set up a stable and clear interference pattern, two conditions must be met:
The sources of the waves must be coherent, which means they emit identical waves with a constant phase difference.
And the waves should be monochromatic - they should be of a single wavelength.
Since the frequency of $y _1$ and $y _2$ is same, they form interference pattern.
Multiple choice physics superposition of waves coherence young's double slit experiment interference

Sources 1 and 2 emit lights of different wavelengths whereas sources 3 and 4 emit lights of different intensities. The coherence

  1. can be obtained by using sources 1 and 2

  2. can be obtained by using sources 3 and 4

  3. cannot be obtained by any of these sources

  4. since contrast suffers when sources 3 and 4 are used so coherence cannot be obtained by using sources 3 and 4
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

the coherence can be  obtained by using sources 3 and 4 as only the intensities are different so their frequencies can be equal
for a coherent sources frequencies must be equal
option $B$ is correct 

Multiple choice physics superposition of waves coherence young's double slit experiment interference

Statement-1: All points on a wavefront vibrate in same phase with same frequency
Statement-2: Two sources are said to be coherent if they produce waves of same frequency with a constant phase difference.

  1. Statement-1 is false, Statement -2 is true

  2. Statement-1 is true, Statement-2 is true; Statement-2 is a correct explanation for Statement-1

  3. Statement-1 is true, Statement-2 is true; Statement-2 is not a correct explanation for statement-1

  4. Statement-1 is true, Statement-2 is false
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

All points on the wavefront have the same temporary displacement. Then need not be oscillating with the same frequency and constant phase difference.
Two wave sources are said to be coherent if they produce waves of same frequency and constant phase difference.
Hence assertion is incorrect, reason is correct. Option A.

Multiple choice physics superposition of waves coherence young's double slit experiment interference

Which of the following is not essential for two sources of light in Young's double slit experiment to produce a sustained interference?

  1. Equal wavelength

  2. Equal intensity

  3. Constant phase relationship

  4. Equal frequency
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For sustainable interference wavelength has to be same. So frequency has to be same too. Contact phase relation is also necessary to sustain the interference pattern else the pattern will keep changing so rapidly that we will not see any pattern.

Equal intensity is not a requirement to keep pattern sustained.

Answer. B) equal intensity