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?

When an object is kept at any distance in front of a concave lens, the image foiled is always:

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 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:

Which of the following can form a virtual image which is always smaller than the object?