Question

If in the following figure, height of object is $H_1=+2.5cm$, then height of image $H_2$ formed is

• A. - 5 cm
• B. + 5 cm
• C. + 7.5 cm
• D. - 7.5 cm

Answer 1

Answer: (A)

By concave mirror formula
$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$
Here $u=-1.5f,f=-f$
we have $\frac{1}{(-f)}=\frac{1}{v}+\frac{1}{(-1.5f)}$
$\therefore \frac{1}{v}=\frac{1}{3f}$ or $v=-3f$
Now, magnification in mirror is given by
$m=\frac{I}{O}=\frac{v}{-u}$
where I is size of image and O is size of object.
Here $0=+2.5cm$
$\therefore \frac{I}{2.5}=\frac{-3f}{(-1.5f)}$ or $I=-5cm$