Tag: interference

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Questions Related to interference

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

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

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

  1. General illumination

  2. Widely separate interference

  3. Very bright maxima

  4. Very dark minima
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

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

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

  1. red

  2. green

  3. yellow

  4. invisible
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

Two sources of light are said to be coherent, when they give light waves of same

  1. amplitude and phase

  2. wavelength and constant phase difference

  3. intensity and wavelength

  4. phase and speed
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency (amplitude may be different).

As $c $ be the speed of light which is constant.
Using, $c= \nu \lambda$
Now same $\nu$ gives same $\lambda.$ for the two light sources.
Example: $y _1= A _1 sin wt$  and $y _2=A _2 sin (wt+\phi) $ where $\phi$ is constant.

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

For interference to take place

  1. sources must be coherent

  2. sources must have same amplitude

  3. waves should travel in opposite directions

  4. sources must have same frequency
Reveal answer Fill a bubble to check yourself
A,D Correct answer
Explanation

For interference to take place source must be coherent, which implies:

  • Same frequency for the two waves
  • Constant phase difference.
Options A and D match.