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Questions Related to physics

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

To demonstrate the phenomenon of interference we require two sources which emit radiation of

  1. nearly the same frequency

  2. the same frequency

  3. different wavelength

  4. the same frequency and having a definite phase relationship
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For stable interference patterns, the two sources must be coherent, meaning they must have the same frequency and a constant phase relationship.

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

Which of the following is not an essential condition for interference?

  1. The two interfering waves must propagate in almost the same direction

  2. The waves must have the same period and wavelength

  3. The amplitudes of the two waves must be equal

  4. The two interfering beams of light must originate from the same source
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When two waves are propagate in same direction

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

If two sources have a randomly varying phase difference $\varphi ( t )$  the resultant intensity will be given by 

  1. $I _ { 0 }$
  2. $\dfrac { I _ { 0 } } { 2 }$
  3. $2 I _ { 0 }$
  4. $\dfrac { I _ { 0 } } { \sqrt { 2 } }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Phase difference is $\phi (t)$,

Since, the phase difference is varying, then the waves are said to be incoherent. So, the intensity of resultant wave is the sum of intensities of each wave i.e. $2\,{{I} _{0}}$ 

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

In a biprism experiment, the distance of 20 th bright bandfrom the center of the interference pattern is 8$\mathrm { mm }$ . The distance of 30th bright band from the center is

  1. $11.8\mathrm { mm }$
  2. 12$\mathrm { mm }$
  3. 14$\mathrm { mm }$
  4. 16$\mathrm { mm }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given

$\begin{array}{l} 20\beta =8mm \ \beta =\dfrac { 8 }{ { 20 } }  \ Now, \ 30th\, \, \max  ima=30\beta =\dfrac { { 30\times \beta  } }{ { 20 } } =12mm \ 30th\, \min  ima=\dfrac { { \left( { 2\left( { 30 } \right) -1 } \right)  } }{ 2 } \beta  \ =\dfrac { { 59 } }{ 2 } \beta  \ =\dfrac { { 59 } }{ 2 } \times \dfrac { 8 }{ { 20 } }  \ =11.8mm \ Hence,\, option\, A\, is\, the\, correct\, answer. \end{array}$

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

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

  1. $0^0$
  2. $360^0$
  3. $720^0$
  4. $90^0$
Reveal answer Fill a bubble to check yourself
D Correct answer
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

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

The time of coherence is of the order of

  1. $10^{-4}s$
  2. $10^{-8}s$
  3. $10^{-6}s$
  4. $10^{-2}s$
Reveal answer Fill a bubble to check yourself
B Correct answer
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($\tau _c$).

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

The time of coherence is of the order of 

  1. $10^{-4}s$
  2. $10^{-8}s$
  3. $10^{-6}s$
  4. $10^{-2}s$
Reveal answer Fill a bubble to check yourself
B Correct answer
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($\tau _c$).

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

Which of the following, cannot produce two coherent sources?

  1. Lloyd's mirror

  2. Fresnel biprism

  3. Young's double sit

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

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

The device which produces highly coherent sources  is

  1. Fresnel biprism

  2. Young's double sit

  3. Laser

  4. Lloyd's mirror
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

Two sources are called coherent if they produce waves

  1. of equal wavelength

  2. of equal velocity

  3. having same shape of wavefront

  4. having a constant phase different
Reveal answer Fill a bubble to check yourself
D Correct answer
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.