A convex lens of focal length 20 cm is placed at adistance of 24 cm from the screen.How far from the lens should an object be placed so as to form real image on the screen.
v(image distance on screen)= 24cm
Using lens formula,
=> 1/24-1/20 =1/u
=> 5-6/120= 1/u
=> -1/120 = 1/u
=> -120cm =u
Therefore Object distance must be 120 cm from the lens.
=> m= 24/-120
=> m= -1/5
Thefore image is real, inverted, diminished(smaller) 5 times and object in turn is placed 120 cms in front of the lens