Physics > Reflection of Light > 5.0 Magnification
Reflection of Light
1.0 Introduction
2.0 Reflection of light
3.0 Basic terminologies of spherical mirrors
3.1 Paraxial approximation
3.2 Spherical mirrors
3.3 Sign convention
3.4 Ray tracing
3.5 Image formation by concave mirror
3.6 Image formation by convex mirror
4.0 Spherical mirror formulae
5.0 Magnification
6.0 Motion of object and image
5.1 Lateral magnification
3.2 Spherical mirrors
3.3 Sign convention
3.4 Ray tracing
3.5 Image formation by concave mirror
3.6 Image formation by convex mirror
The lateral magnification is also known as transverse or linear magnification.
It is represented as $m$.
It is defined as, $$m = \frac{{{\text{height of image}}}}{{{\text{height of object}}}} = \frac{{II'}}{{OO'}}\quad ...(i)$$
From $\Delta OO'P$ and $\Delta II'P$, $$\begin{equation} \begin{aligned} \angle OO'P = \angle II'P = 90^\circ \\ \angle O'PO = \angle IPI' = \theta \\\end{aligned} \end{equation} $$ So, $$\Delta OO'P \approx \Delta II'P$$ Therefore, $$\begin{equation} \begin{aligned} \frac{{ - I'I}}{{O'O}} = \frac{{ - v}}{{ - u}} \\ \frac{{I'I}}{{O'O}} = - \frac{v}{u}\quad ...(ii) \\\end{aligned} \end{equation} $$
From equation $(i)$ and $(ii)$ we get, $$m = - \frac{v}{u}$$
Note:
- $-ve$ sign implies that image is inverted with respect to the object.
- $+ve$ sign implies that image is erect with respect to the object.
