Question

Consider a concave mirror of $10\, cm$ focal length illuminated by an object kept at a distance of $25\, cm$. The distance at which the image is formed and its magnification respectively are

• A. -16.7 cm and -0.67
• B. 7.1 cm and 0.29
• C. -16.7 cm and 0.67
• D. 7.1 cm and -0.29

Answer 1

Answer: (A)

Using mirror equation, we have,
$\frac{1}{v}+\frac{1}{u} =\frac{1}{f}$
or $\frac{1}{v} =\frac{1}{f}-\frac{1}{u}$
$\Rightarrow \frac{1}{v}=\frac{1}{(-10)}-\frac{1}{(-25)}$
[$\therefore $ Given $f=-10\, cm ,\, u=-25\, cm$ ]
$\Rightarrow v=-16.7\, cm$ and magnification,
$m=-\left(\frac{v}{u}\right)=\frac{-(-16.7)}{-25}=-0.67$