Question

What is meant by magnification ? Write its expression. What is its sign for the (a) real and (b) virtual image ?

Answer 1

Magnification is the process of expanding something's perceived size rather than its real size. This expansion is measured by a numerical value known as "magnification." When this value is less than one, it denotes a size decrease, often known as minification or de-magnification. Magnification is usually associated with enlarging visuals or pictures to view more detail, improving resolution, using a microscope, printing methods, or digital processing. The magnification of a picture does not affect the viewpoint of the image in any situation.

Complete answer:
The Lens formula describes the relationship between the distance of an image (v) the distance of an object (u), and the focal length (f) of the lens in optics. The lens formula works for both convex and concave lenses. The thickness of these lenses is minimal. For a spherical mirror, it is an equation that connects the focal length, image distance, and object distance. It's written as,
$\dfrac{1}{v}+\dfrac{1}{u}=\dfrac{1}{f}$
$v$= distance of the image from the lens
$u$= distance of the object from the lens
$f$= focal length of the lens

The ratio of the height of an image to the height of an object is defined as the magnification of a lens. It's also expressed in terms of picture and object distances. It equals the picture distance divided by the object distance.
$\text{m=}\dfrac{\text{v}}{\text{u}}\text{=}\dfrac{\text{height of image}}{\text{height of object}}$
(a) In a real image, the $u$ and $v$ values are negative. As a result, $m$ is negative.
(b) In a virtual picture, $u$ denotes a negative value and $v$ denotes a positive value. As a result, $m$ is a positive number.

Note: The degree of convergence or divergence of light rays landing on a lens is measured by its power. The degree of convergence or divergence is determined by the lens' focal length. As a result, the lens' power is defined as the reciprocal of the focal length of the lens in use. The dioptre is the SI unit of power (D). The concave lens has a negative power, whereas the convex lens has a positive power.