Question

An object is placed at a distance of 6cm from a concave lens of focal length 18cm. Find position of image​

Answer 1

Answer:

The mirror formula is 1u+1v=1f, where,

u is the distance of the object from the mirror,

v is the distance of the image from the mirror, and,

f is the focal length of the mirror.

As per the sign convention, distances to the right of the mirror are termed positive and the distances to the left are termed negative, with the reflecting surface of the mirror facing the left.

In concave mirrors the the object, image and focus are all to the left of the mirror. Hence the values of all these distances have a negative sign.

It is given that u=−6 cm and v=−18 cm.

⇒−16−118=1f⇒1f=−29.

⇒f=−92=−4.5 cm.

⇒ The focal length is 4.5 cm.