Question

an object 60 centimetre from a lens gives a virtual image at a distance 20 centimetre in front of the lens what is the focal length of the lens is the lens converging or diverging give the reason for your answer

Answer 1

given ,

u=-60 cm
v=20cm
now use formula ,
1/v - 1/u=1/f

1/20 -1/(-60) =1/f

1/20 +1/60=1/f

4/60 =1/f

f=15cm
focal length f=+15cm hence lens is conveging .