Tag: wave optics

Quizzes (12) Questions (312)

Questions Related to wave optics

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

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

  1. $\displaystyle\frac{1.5\lambda}{(\mu-1)}$
  2. $\displaystyle{1.5}{(\mu-1)\lambda}$
  3. $\displaystyle{2.5}{(\mu-1)\lambda}$
  4. $\displaystyle\frac{2.5\lambda}{(\mu-1)}$
Reveal answer Fill a bubble to check yourself
D Correct answer
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, $t=\dfrac{2.5\lambda}{(\mu-1)}$

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

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

  1. $d=\sqrt{d _1d _2}$
  2. $d=2a(\mu-1)a$
  3. $d=\displaystyle\frac{D\lambda}{\beta}$
  4. $d=\displaystyle\sqrt\frac{d^2 _1}{d _2}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

 $d=\sqrt{d _{1}d _{2}}$.

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

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

  1. interference

  2. reflection

  3. refraction

  4. total internal reflection
Reveal answer Fill a bubble to check yourself
C Correct answer
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

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

Which of the following statements is correct?

  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.
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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 

  1. $10cm$
  2. $12cm$
  3. $14cm$
  4. $15cm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In the displacement method for a biprism, the distance between the virtual slits d = sqrt(d1 * d2). Here, d = sqrt(16 * 9) = sqrt(144) = 12 cm.

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

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?

  1. $\dfrac{3\lambda}{2c}$
  2. $\dfrac{2\lambda}{c}$
  3. $\dfrac{3\lambda}{c}$
  4. $\dfrac{4\lambda}{c}$
Reveal answer Fill a bubble to check yourself
C Correct answer
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 = $\dfrac{Distance}{Speed}$
        = $\dfrac{3\lambda}{c}$
Multiple choice physics wave optics difference between interference and diffraction explaining wave phenomena diffraction

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 :

  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. $2.63\ mm^2, 0.22\ mm$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Area of the n-th HPZ is A = pi * b * lambda. For n=1, A = pi * 1 * 500 * 10^-9 = 1.57 * 10^-6 m^2 = 1.57 mm^2. Radius of n-th HPZ is r_n = sqrt(n * b * lambda). For n=3, r_3 = sqrt(3 * 1 * 500 * 10^-9) = sqrt(1500 * 10^-9) = 1.22 * 10^-3 m = 1.22 mm.

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

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

  1. one

  2. two

  3. zero

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