Introduction to Light

What is a light?

Light is a form of energy that excites our sense of sight and helps us see.

How is an object visible?

An object is visible if it is itself a source of light or if it reflects light falling on it. It needs a suitable instrument like eye to observe the light coming from such objects.

How does light travel?

Light moves in a straight line, in a rectilinear path, in vacuum or a homogeneous transparent medium. The path of light as it moves in straight line is called as ray of Light. The collection of such rays is beam. The beam is parallel if the rays remain parallel. If the rays of a beam meet at a single point, it is called as convergent beam. When the rays spread out from a single point, they form divergent beam. A beam of light undergoes either reflection or refraction (or both) when it encounters an object.

What is an image?

An image is a visual replica of an object. It produces the same pattern of light combination emitted by the object.

Differentiate real and virtual images.

A real image of a point object is a physical convergence of light rays coming from that point that can be captured.A virtual image of the object is an apparent convergence the light rays that exists only in perception. In fact, the light rays appear to come from the point image (diverge).

Light actually comes from real image while it appears to come from virtual image.
A real image can be projected on a screen but a virtual image cannot be projected on a screen.
Real images formed by a single lens or mirror are usually inverted (upside down) while virtual images formed by a single lens or mirror are mostly upright (erect).
For example, image on a cinema screen is real image but that seen through a plane mirror is virtual image.