Ray Optics · JEE Main previous year questions

A plano convex lens of refractive index $1.5$ and radius of curvature $30\mathrm{cm}$ is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of size of the object

1. A.$60\mathrm{cm}$
2. B.$30\mathrm{cm}$
3. C.$20\mathrm{cm}$
4. D.$80\mathrm{cm}$

A light ray is incident perpendicularly to one face of a $90^{\circ }$ prism and is totally internally reflected at the glass-air interface. If the angle of reflection is $45^{\circ }$, we conclude that the refractive index $n$

1. A.$n>\frac{1}{\sqrt{2}}$
2. B.$n>\sqrt{2}$
3. C.$n<\frac{1}{\sqrt{2}}$
4. D.$n<\sqrt{2}$

An astronomical telescope has a large aperture to

1. A.reduce spherical aberration
2. B.have high resolution
3. C.increase span of observation
4. D.have low dispersion

If two mirrors are kept at $60^{\circ }$ to each other, then the number of images formed by them is

1. A.$5$
2. B.$6$
3. C.$7$
4. D.$8$

Which of the following is used in optical fibres?

1. A.total internal reflection
2. B.scattering
3. C.diffracttion
4. D.refraction