Magnification In Lenses MCQ - Practice Questions with Answers

Magnification in Lenses-

Magnification produced by a lens is defined as the ratio of size of the image to that of the object. 

For the derivation let an object is palced whose height is h and the image height is h'. Let us consider an object is placed on the principal axis with its height h perpendicular to the principal axis as shown in figure. The first ray is passing through the optic centre will go undeviated. The second ray parallel to the principal axis must pass through the focus F' The image is formed where both the light rays intersect. By this we get an image of height h'. So mathematically, magnification can be written as - 

$$
\mathbf{m}=\frac{\mathbf{h}^{\prime}}{\mathbf{h}}
$$

Like mirror we can derive the formula of magnification in terms of the position of object and image. For this, consider the figure given below -

As the triangle OO'P and II'P, is similar so we can write that -

$$
\frac{I^{\prime} I}{O O^{\prime}}=\frac{P I}{P O}
$$

So,

$$
\frac{h^{\prime}}{h}=\frac{v}{u}
$$

$$
m=\frac{h^{\prime}}{h}=\frac{v}{u}
$$