a concave lens has focal length of 20cm. calculate at what distance from the lens should a object be placed so that it forms an image at 15cm from the lens.also calculate the size of image formed
Answers
Answered by
0
f= -20
v= -15
u=?
by lens formula->
1/f= 1/v - 1/u
1/-20= 1/-15 - 1/u
1/-20 + 1/15 = _ 1/u
7/60 = 1/u
7 u = 60
u= 60/7
u= 8.57.
hence,
the object should be placed at a distance of 8.57 cm from the lens.
v= -15
u=?
by lens formula->
1/f= 1/v - 1/u
1/-20= 1/-15 - 1/u
1/-20 + 1/15 = _ 1/u
7/60 = 1/u
7 u = 60
u= 60/7
u= 8.57.
hence,
the object should be placed at a distance of 8.57 cm from the lens.
Similar questions