Ray Optics · JEE Main previous year questions

2017 2 questions

1. Q412017 · 9 Apr 2017 · Shift 1

   In an experiment a convex lens of focal length 15 cm is placed coaxially on an optical bench in front of a convex mirror at a distance of 5 cm from it. It is found that an object and its image coincide, if the object is placed at a distance of 20 cm from the lens. The focal length of the convex mirror is :

   1. A.27.5 cm
   2. B.20.0 cm
   3. C.25.0 cm
   4. D.30.5 cm
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   Answer: A

2. Q502017 · 8 Apr 2017 · Shift 1

   Let the refractive index of a denser medium with respect to a rarer medium be ${\mathrm{n}}_{12}$ and its critical angle be ${\theta }_{\mathrm{C}}$. At an angle of incidence A when light is travelling from denser medium to rarer medium, a part of the light is reflected and the rest is refracted and the angle between reflected and refracted rays is $90^{\circ }$. Angle A is given by :

   1. A.$\frac{1}{{\cos }^{-1}(\sin {\theta }_C)}$
   2. B.$\frac{1}{{\tan }^{-1}(\sin {\theta }_C)}$
   3. C.${\cos }^{-1}(\sin {\theta }_C)$
   4. D.${\tan }^{-1}(\sin {\theta }_C)$
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   Answer: D