Wave Optics · JEE Main previous year questions

2018 3 questions

1. Q492018 · 16 Apr 2018 · Shift 1

   Unpolarized light of intensity I is incident on a system of two polarizers, A followed by B. The intensity of emergent light is I/2. If a third polarizer C is placed between A and B, the intensity of emergent light is reduced to I/3. The angle between the polarizers A and C is $\theta$. Then :

   1. A.$\cos \theta ={\left(\frac{2}{3}\right)}^{1/2}$
   2. B.$\cos \theta ={\left(\frac{2}{3}\right)}^{1/4}$
   3. C.$\cos \theta ={\left(\frac{1}{3}\right)}^{1/2}$
   4. D.$\cos \theta ={\left(\frac{1}{3}\right)}^{1/4}$
   Show answer

   Answer: B

2. Q522018 · 8 Apr 2018 · Shift 1

   The angular width of the central maximum in a single slit diffraction pattern is $60^{\circ }$. The width of the slit is $1\mu \text{m}$. The slit is illuminated by monochromatic plane waves. If another slit of same width is made near it, Young's fringes can be observed on a screen placed at a distance 50 cm from the slits. If the observed fringe width is 1 cm, what is slit separation distance? (i.e. distance between the centres of each slit.)

   1. A.$100\mu \text{m}$
   2. B.$25\mu \text{m}$
   3. C.$50\mu \text{m}$
   4. D.$75\mu \text{m}$
   Show answer

   Answer: B

3. Q532018 · 8 Apr 2018 · Shift 1

   Unpolarized light of intensity I passes through an ideal polarizer A. Another identical polarizer B is placed behind A. The intensity of light beyond B is found to be I/2. Now another identical polarizer C is placed between A and B. The intensity beyond B is now found to be I/8. The angle between polarizer A and C is :

   1. A.$60^{\circ }$
   2. B.$30^{\circ }$
   3. C.$45^{\circ }$
   4. D.$0^{\circ }$
   Show answer

   Answer: C