Question

An object placed at 20 cm from a concave mirror forms a real inverted image at a distance of 40 cm from a concave mirror. Find the focal length of the concave mirror? answer- focal length 13.33 cm ​

Answer 1

Answer:

The focal length of the concave mirror will be 13.33 cm.

Explanation:

The image will also be formed in front of the mirror since it is real and inverted.

The image distance from the mirror, v = -40 cm

The object distance from the mirror, u = -20 cm

The mirror formula is given as:

 1/f = 1/u + 1/v

⇒ f = uv / (u + v)

   f = (-20 × -40) / (-20 + -40)

   f = 800 / -60

   f = -13.33 cm

The focal length of a concave mirror is always negative.

Answer 2

Answer:

u= (-20 cm)

u= (-20 cm)v= (+40 cm)

u= (-20 cm)v= (+40 cm)f= ?

u= (-20 cm)v= (+40 cm)f= ?1/v + 1/u = 1/f

u= (-20 cm)v= (+40 cm)f= ?1/v + 1/u = 1/f1/40 - 1/20 = 1/f

u= (-20 cm)v= (+40 cm)f= ?1/v + 1/u = 1/f1/40 - 1/20 = 1/f(1-2)/40 = 1/f

u= (-20 cm)v= (+40 cm)f= ?1/v + 1/u = 1/f1/40 - 1/20 = 1/f(1-2)/40 = 1/f-1/40 = 1/f

u= (-20 cm)v= (+40 cm)f= ?1/v + 1/u = 1/f1/40 - 1/20 = 1/f(1-2)/40 = 1/f-1/40 = 1/ff = -40 cm