A lens of focal length f produces an image of an object located 30 cm on one side of it at a distance of 60 cm?

A lens of focal length f produces an image of an object located 30 cm on one side of it at a distance of 60 cm on the other side. If the lens is replaced by another of 3f/4, where would the image form? If the image has to form at the earlier position by what distance should the object be shiftedA lens of focal length f produces an image of an object located 30 cm on one side of it at a distance of 60 cm?
Here, u= - 30 and v = 60 where u=object distance v=image distance





Using lens formula,


1 / v -1 / u = 1 / f





1 / 60 -(- 1/ 30) = 1/f





which gives f = 20 cm





Now 3 /4 f = 3/4 * 20 = 15 cm





Using lens formula again,





1/v - (- 1/30) = 1/15





we get v = + 30 cm





i.e. image is formed at distance of 30 cm at other side of lens





For image to form at v = + 60 cm (earlier position)





1/60 - 1/u = 1/15 (by lens formula again)





u = - 20 cm





Earlier object was at u = -30 cm


So the object should be shifted by 10 cm towards the lens





Hope it helped!!!!A lens of focal length f produces an image of an object located 30 cm on one side of it at a distance of 60 cm?
1/o+1/i=1/f


1/30+1/60=1/20


f=20


3(20)/4=15


1/30+1/i=1/15


i=30


for the second part


1/o+1/60=1/15


o=20


which means the object should be shifted 10 cm to the right, towards the lens.