A boy is trying to start a fire by focusing sunlight on a piece of paper using an equiconvex lens of focal length 10 cm. The diameter of the sun is 1.39 x10⁹ m and its mean distance from the earth is 1.5 x 10¹¹ m. What is the diameter of the sun's image on the paper?

1.  $9.2\times {10}^{-4} \mathrm{m}$

2.  $6.5\times {10}^4 \mathrm{m}$

3.  $6.5\times {10}^{-5} \mathrm{m}$

4.  $12.4\times {10}^{-4} \mathrm{m}$

A small coin is resting on the bottom of a beaker filled with a liquid. A ray of light from the coin travels up-to-the surface of the liquid and moves along its surface(see figure). 
 
How fast is the light traveling in the liquid?

1. $1.8\times {10}^8 m/s$

2. $2.4\times {10}^8 m/s$

3. $3.0\times {10}^8 m/s$

4. $1.2\times {10}^8 m/s$

The frequency of a light wave in a material is 2×10¹⁴ Hz and wavelength is 5000 Å. The refractive index of material will be:

1. 1.40

2. 1.50

3. 3.00

4. 1.33

A microscope is focussed on a mark on a piece of paper and then a slab of glass of thickness 3 cm and refractive index 1.5 is placed over the mark. How should the microscope be moved to get the mark in focus again?

1. 1 cm upward

2. 4.5 cm downward

3. 1 cm downward

4. 2 cm upward

A convex lens and a concave lens, each having the same focal length of 25 cm, are put in contact to form a combination of lenses. The power in dioptres of the combination is :

1. 25

2. 50

3. infinite

4. zero

Pick the wrong statement in the context with a rainbow.

1. Rainbow is a combined effect of dispersion, refraction, and reflection of sunlight.

2. When the light rays undergo two internal reflections in a water drop, a secondary rainbow is formed.

3.  The order of colors is reversed in the secondary rainbow.

4. An observer can see a rainbow when his front is towards the sun.

Two similar thin equi-convex lenses, of focal length f each, are kept coaxially in contact with each other such that the focal length of the combination is $F_1$. When the space between the two lenses is filled with glycerin which has the same refractive index ($\mu =1.5$) as that of glass, then the equivalent focal length is $F_2$. The ratio $F_1:F_2$ will be:

1. 3 : 4

2. 2 : 1

3. 1 : 2

4. 2 : 3

A ray of light falls on a plane mirror A kept at an angle 90$°$ to mirror B as shown in the figure. The angle N is :

1.  30$°$

2.  45$°$

3.  60$°$

4.  90$°$

Which of the following ray diagrams is correct?

1.  

2.  

3.  

4.  

A concave lens gives a virtual image. In optical lenses worn by humans which of the following statements is true?

1.  The lens can never be concave.

2.  In some cases, the lens can be concave if the focal length is much larger than 2.5 cm.

3.  All focal length concave lenses are possible.

4.  All focal length Convex lenses are possible.