Question

An object of height 10 cm is placed at a distance 100 cm before the convex mirror perpendicular below the principal axis. If the focal length of the mirror is 10 cm, on applying the Cartesian sign convention. Find the signs of object distance, focal length and height of the object.

• A. $u=100cm,f=-10cm,h=-10cm$
• B. $u=100cm,f=10cm,h=20cm$
• C. $u=100cm,f=-10cm,h=10cm$
• D. $u=-100cm,f=10cm,h=10cm$

Answer 1

The correct option is D $u=-100cm,f=10cm,h=10cm$

According to the rules of sign convention,(a) distances are measured from the mirror.(b) distances measured along the direction of incident rays are taken positive and (c) distances measured opposite to the direction of incident rays are taken negative.
Hence,$u=-100cm,h=10cmandf=10cm$.