A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. What is the focal length of the concave mirror?

see full answer

Your Exam Success, Personally Taken Care Of

1:1 expert mentors customize learning to your strength and weaknesses – so you score higher in school , IIT JEE and NEET entrance exams.

An Intiative by Sri Chaitanya

answer is B.

(Unlock A.I Detailed Solution for FREE)

Best Courses for You

JEE

NEET

Foundation JEE

Foundation NEET

CBSE

Detailed Solution

Concept: We'll start by determining the object's distance from the pole using the relationship between the magnifying ratio of the image and the object distance. After that, using the relationship between the image and the object distance from the pole, the focal length of the mirror may be estimated.
The focal length of a concave mirror can be determined by

Where f= focal length of the mirror
v=distance of the image from the pole
u=Distance of the object from the pole
In the above question, it is given that the image is formed in front of the mirror, so the image is real and is at a distance of 30 cm from the pole
So v= -30 cm