When sunlight is concentrated on a piece of paper by a spherical mirror or lens, then a hole can be burnt in it. For doing this, the paper must be placed at the focus of:

A beam of parallel light rays is incident through the holes on one side of a box and emerges out through the holes on its opposite side as shown in the diagram below.

Which of the following could be inside the box?

A beam of light is incident through the holes on one side of a box and emerges out through the holes on its opposite side as shown in the following figure.

The box contains:

When an object is placed $10 \mathrm{cm}$ in front of lens $A$, the image is real, inverted, magnified and formed at a great distance. When the same object is placed $10 \mathrm{cm}$ in front of lens $B$, the image formed is real, inverted and same size as the object.

What is the focal length of lens $A$?

When an object is placed $10 \mathrm{cm}$ in front of lens $A$, the image is real, inverted, magnified and formed at a great distance. When the same object is placed $10 \mathrm{cm}$ in front of lens $B$, the image formed is real, inverted and same size as the object.

What is the focal length of lens $B$?

When an object is placed $10 \mathrm{cm}$ in front of lens $A$, the image is real, inverted, magnified and formed at a great distance. When the same object is placed $10 \mathrm{cm}$ in front of lens $B$, the image formed is real, inverted and same size as the object.

What is the nature of lens $A$?

When an object is placed $10 \mathrm{cm}$ in front of lens $A$, the image is real, inverted, magnified and formed at a great distance. When the same object is placed $10 \mathrm{cm}$ in front of lens $B$, the image formed is real, inverted and same size as the object.

What is the nature of lens $B$?

When a fork is seen through lenses $A$ and $B$ one by one, it appears as shown in the diagrams. What is the nature of (i) lens $A$ and (ii) lens $B$? Give reason for your answer.