Finding focal length
Used as a magnifying glass, the image of an object 4cm from a converging lens is five times the object length. What is the focal length of the lens?
I used m=v/u=5
v=4*5=20cm
the i used 1/v+1/u=1/f
1/20+1/4=1/f
f=3.33cm
the problem is here, the image is supposed to be same way up and virtual, that means that the focal length is greater than the object distance u. the answer is supposed to be 5cm.
where have i gone wrong?
