Question

The real image which is exactly equal to the size of an object is to be obtained on a screen with the help of a convex glass of focal length 15 cm. For this, what must be in the distance between the object and the screen?

Answer 1

Answer:

Distance of object from screen = 60 cm

Explanation:

Focal length (f) = +15 cm

Magnification = -1

⇒ $\frac{v}{u}$ = -1

⇒ v = -u ----> (1)

From lens formula ,

$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$

⇒ $\frac{1}{15} = -\frac{1}{u} - \frac{1}{u}$

⇒ $\frac{1}{15} = -\frac{2}{u}$

⇒ u = -30 cm

∴ The distance of object from screen = v + u(only integral value) = 60 cm