Tag: interference

Questions Related to interference

Two coherent waves of light will not produce constructive interference if the phase difference between them is

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

  1. $0^0$

  2. $360^0$

  3. $720^0$

  4. $90^0$

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Correct Option: D
Explanation:

Constructive interference for coherent waves takes place when phase difference = $2n\pi$ where n is a integer

So the only case in the options when constructive interference will not take place is $90^\circ$

Answer. D

The time of coherence is of the order of

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

  1. $10^{-4}s$

  2. $10^{-8}s$

  3. $10^{-6}s$

  4. $10^{-2}s$

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Correct Option: B
Explanation:

In a light source, a light wave(photon) is produced when an excited atom goes to the ground state and emits light.

The duration of this transition is $10^{-8}s$. Thus the emitted wave remains sinusoidal for this much time. This time is known as coherence time($\tau _c$).

The time of coherence is of the order of 

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

  1. $10^{-4}s$

  2. $10^{-8}s$

  3. $10^{-6}s$

  4. $10^{-2}s$

Show answer
Correct Option: B
Explanation:

In a light source(photon) is produced when an excited atom goes to the ground state and emits light.

The duration of the transition is about $10^{-8}s$. Thus the emitted light remains sinusoidal for this much time. This is called the coherence time($\tau _c$).

Which of the following, cannot produce two coherent sources?

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

  1. Lloyd's mirror

  2. Fresnel biprism

  3. Young's double sit

  4. Prism

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Correct Option: D
Explanation:

Two coherent sources are produced in Lloyd's mirror by reflection of light from a plane mirror, hence the original source and its image acting as coherent sources.

In fresnel biprism, light from a point source gets refracted by a biprism to produce two coherent sources.
In Young's double slit, two coherent sources are produced by passing of light from a single source through two slits.

The device which produces highly coherent sources  is

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

  1. Fresnel biprism

  2. Young's double sit

  3. Laser

  4. Lloyd's mirror

Show answer
Correct Option: C
Explanation:

The atoms in the laser medium are pumped up energetically by an external power source, producing a population inversion of atomic energies. The pumped-up atoms can return to lower energy levels by emitting light at only certain frequencies, depending on the particular medium, which can be a solid (e.g. laser diode), a liquid (e.g. dye laser) or a gas (e.g. helium-neon laser).

We get temporal coherence because the excited atoms emit only at that preferred frequency.

Two sources are called coherent if they produce waves

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

  1. of equal wavelength

  2. of equal velocity

  3. having same shape of wavefront

  4. having a constant phase different

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Correct Option: D
Explanation:

Two source are called coherent, if they have constant phase difference i.e., phase difference between two wave is constant with respect to time.

Coherence is a measure of

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

  1. capability of producing interference by wave

  2. waves being diffracted

  3. waves being reflected

  4. waves being refracted

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Correct Option: A
Explanation:

Interference is a phenomenon in which two waves superpose to form a resultant wave of greater or lower amplitude.

If the sources are coherent, the interference pattern obtained is more ordered, with definite spacing between fringes. 
Thus coherence is a measure of capability of producing interference of wave.

The phenomenon of interference is shown by:

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

  1. longitudinal mechanical waves only

  2. electromagnetic waves only

  3. transverse mechanical waves only

  4. all the above types of waves

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Correct Option: D
Explanation:

All of the above type of waves.


Interference of a wave is the phenomenon that usually happens when the two waves reinforce,while travelling in the same medium. The interference of waves causes the medium to take on a shape that results from the net effects of the two individual waves simultaneously acting upon the particles of the medium.

Two coherent sources of light can be obtained by

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

  1. two different lamps

  2. two different lams of same power and same colour

  3. two different lamps of same power

  4. none of these

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Correct Option: D
Explanation:

Two sources are said to be coherent if they have exactly same frequency and have zero or constant phase difference. Two coherent source cannot be obtained from two different light sources.

Two light sources are said to be coherent if they are obtained from:

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

  1. two ordinary bulbs emitting light of different wavelengths

  2. a single point source

  3. a wide source

  4. two independent point sources emitting light of the same wavelength

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Correct Option: B