Question

An object and its real image are located at distances $25cm$ and $40cm$ respectively from the two principle focii of a convex lens. The linear magnification of the image is near to

• A. 1.3
• B. -1.3
• C. 1.8
• D. -1.8

Answer 1

The correct option is B -1.3

From the figure

$\begin{array}{c}u=-(25+\varphi )\\ v=(40+\varphi )\end{array}$

wing lene of ormula we get

$\begin{array}{cc}\frac{1}{v}-\frac{1}{u}& =\frac{1}{f}\\ \frac{1}{F+40}& +\frac{1}{25+f}=\frac{1}{F}\end{array}$

$F(25+F)+F(40+F)=(40+f-)(25+F)$

$\begin{array}{cc}& F^2=1000\\ F& =31.62cm\\ \omega =& 25+31.62=56.62cm\\ v=& 40+31.62=71.62cm\\ m=\frac{v}{u}=\frac{71.62}{-56.62}& \\ m=-1.3& \end{array}$

Hence option (B) is correct