Tag: wave optics

Questions Related to wave optics

In a bi-prism experiment fifth dark fringes are obtained at a point. If a thin transparent film is placed in the path of one of waves, then seventh bright fringe is obtained at the same point. The thickness of the film in terms of wavelength $X$ and refractive index $\mu$ will be

physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

  1. $\displaystyle\frac{1.5\lambda}{(\mu-1)}$

  2. $\displaystyle{1.5}{(\mu-1)\lambda}$

  3. $\displaystyle{2.5}{(\mu-1)\lambda}$

  4. $\displaystyle\frac{2.5\lambda}{(\mu-1)}$

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Correct Option: D
Explanation:

For 5th dark fringe to be obtained at the point, the path difference of the beams at that point =$\dfrac{9\lambda}{2}$.

For 7th bright fringe to be obtained at the same point, the new path difference of the beams at that point =$7\lambda$.
Due to insertion of the film of thickness $t$, path difference added to the beam=$t(\mu-1)$
Hence, $\dfrac{9\lambda}{2}+t(\mu-1)=7\lambda$
Hence, $t=\dfrac{2.5\lambda}{(\mu-1)}$

The refracting angle of bi-prism is

physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

  1. $179^0$

  2. $1^0$

  3. $0.5^0$

  4. $90^0$

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Correct Option: C
Explanation:
The refracting angles of the bi- prism are very small, usually about $0.5^o$

In bi-prism experiment the light source is

physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

  1. extented

  2. narrow

  3. multichromatic

  4. all the above

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Correct Option: B
Explanation:

For the sustained interference of light wave , two source must be narrow.

Which of the following formulae is incorrect in a bi-prism?

physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

  1. $d=\sqrt{d _1d _2}$

  2. $d=2a(\mu-1)a$

  3. $d=\displaystyle\frac{D\lambda}{\beta}$

  4. $d=\displaystyle\sqrt\frac{d^2 _1}{d _2}$

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Correct Option: D
Explanation:

If $d _{1}$, $d _{2}$ are the distances of two virtual sources from the central axis, the average $d$ is given by

 $d=\sqrt{d _{1}d _{2}}$.

In Fresnel's bi-prism experiment, the coherent sources are obtained by

physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

  1. interference

  2. reflection

  3. refraction

  4. total internal reflection

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Correct Option: C
Explanation:

In Fresnel bi-prism, light from the single source are made into two virtual sources on passing it through the bi-prism due to refraction in prism, so that the two sources acts as a coherent sources

Which of the following statements is correct?

physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

  1. Diffraction is because of interference of light from same sources whereas interference is due to light form two isolated sources.

  2. Diffraction is due to interaction of light from same wave fronts whereas interference is due to interaction of two waves derived from the same source.

  3. Diffraction is due to interference of waves derived from the same source whereas interference is bending of light from the same source.

  4. Diffraction is due to reflected waves whereas interference is due to transmitted waves from a source.

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Correct Option: B
Explanation:

When a same source is present, it might give different colours depending on the path difference between the interfering rays from the source.

However when two completely different sources are present, they interfere due to path difference between them and give the interference pattern. For example, Young' double slit experiment.

In a Fresnel's biprism experiment the two positions of lens separation between the slits as $16cm$ and $9cm$ respectively. The true distance of separation between the slits is 

physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

  1. $10cm$

  2. $12cm$

  3. $14cm$

  4. $15cm$

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Correct Option: B

A monochromatic plane wave of speed c and wavelength $\lambda$ is diffracted at a small aperture. The diagram illustrates successive wave fronts.
After what time will some portion of the wave front GH reach point P?

physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

  1. $\dfrac{3\lambda}{2c}$

  2. $\dfrac{2\lambda}{c}$

  3. $\dfrac{3\lambda}{c}$

  4. $\dfrac{4\lambda}{c}$

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Correct Option: C
Explanation:
The distance between two consecutive lines(wavefronts ) ia $\lambda$.
So, wavefront XY is separated by a distance of 3λ from the wavefront that has reached point P.

Distance that needs to be travelled = $3\lambda$
Speed of light = $c$

Speed =$\dfrac{Distance}{time}$
Time = $\dfrac{Distance}{Speed}$
        = $\dfrac{3\lambda}{c}$

A screen is at a distance of $1\ m$ away from the aperture. If light of wavelength $500\ nm$ falls on an aperture, then area of first HPZ and radius of third HPZ are :

physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

  1. $1.57\ mm^2, 1.22\ mm$

  2. $1.22\ mm^2, 1.57\ mm$

  3. $1.65\ mm^2, 2.79\ mm$

  4. $2.63\ mm^2, 0.22\ mm$

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Correct Option: A

The phenomenon of diffraction can be treated as interference phenomenon if the number of coherent sources is 

physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

  1. one

  2. two

  3. zero

  4. infinity

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Correct Option: D
Explanation:

The single slit diffraction pattern acts as an envelope for the multiple slit interference patterns.

Diffraction on a single slit is equivalent to interference of light from infinite number of coherent sources contained in slit.