Question

Define Refractive Index. Differentiate between real and virtual images formed by a lens.

Hint:

Convex lenses can form both real and virtual images depending on object position, while concave lenses always form virtual images.

Answer 1

Refractive Index:
The refractive index of a medium is defined as the ratio of the speed of light in vacuum to the speed of light in that medium.

Mathematically,
n = c / v

where c is the speed of light in vacuum and v is the speed of light in the given medium. It can also be defined as the ratio of the sine of the angle of incidence to the sine of the angle of refraction when light passes from one medium to another.

Difference between Real and Virtual Images formed by a Lens:

1. Formation:
A real image is formed when light rays actually converge (meet) after refraction through the lens.
A virtual image is formed when light rays appear to diverge from a point but do not actually meet.

2. Nature of Image:
A real image is generally inverted.
A virtual image is generally erect.

3. Position:
A real image is formed on the opposite side of the lens from the object.
A virtual image is formed on the same side of the lens as the object.

4. Screen Formation:
A real image can be obtained on a screen.
A virtual image cannot be obtained on a screen.

Conclusion:
Thus, the refractive index measures how much light slows down in a medium, and real and virtual images formed by a lens differ in formation, nature, position, and whether they can be projected on a screen.