Solve the following examples.
An object kept 60 cm from a lens gives a virtual image 20 cm in front of the lens. What is the focal length of the lens? Is it a converging lens or diverging lens?
Answer:
As per the question
The object distance is u=-60cm
Virtual image is v =-20cm
⇒ 
⇒ f= -30cm
From above we can conclude that as the focal length is negative it is diverging in nature and is a concave lens.
