Tag: superposition of waves

Questions Related to superposition of waves

Two light sources are coherent when:

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

  1. Only their frequency are equal

  2. their wavelength are equal

  3. Their amplitudes are equal

  4. Time frequency are equal and their phase

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Correct Option: B

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

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

  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

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Correct Option: B
Explanation:

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

In Lloyd's single mirror method we have

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

  1. Both sources virtual

  2. One source virtual and one real

  3. Both sources real

  4. None of these

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Correct Option: B
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.

In coherent sources it is necessary that their

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

  1. amplitudes are same

  2. wavelengths are same

  3. initial phase remains constant

  4. None of these

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Correct Option: C
Explanation:

For sources to be coherent it is necessary that their initial phase difference remains the same or constant.

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 

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

  1. $y _1$ and $y _2$

  2. $y _2$ and $y _3$

  3. $y _1$ and $y _3$

  4. Interference will not possible

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Correct Option: A
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.

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

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

  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

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Correct Option: B
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 

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.

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

  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

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Correct Option: A
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.

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

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

  1. Equal wavelength

  2. Equal intensity

  3. Constant phase relationship

  4. Equal frequency

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Correct Option: B
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

Instead of using two slits, if we use two separate identical sodium lamps in Young's experiment, which of the following will occur?

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

  1. General illumination

  2. Widely separate interference

  3. Very bright maxima

  4. Very dark minima

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Correct Option: A
Explanation:

There will be general illumination as super imposing waves do not have constant phase difference.

In Young's double slit experiment, one slit is covered with red filter and another slit is covered by green filter, then interference pattern will be

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

  1. red

  2. green

  3. yellow

  4. invisible

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Correct Option: D
Explanation:

When the red and green filters are used, the rays from slits will have wavelengths of red and green light.  The condition of mono chromatic sources will not be met. Hence, the fringe pattern will disappear.