the size of the image after an object by a convex lens of focal length 20cm is observed to be reduced to 1/3rd of its size. find the distance of the object from its optical centre of the lens.
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It is
Incorrect. Because you need to take h' = -h/3. So m=-1/3.
The answer is -80 cm
If the answer was -40cm, then the size of image will be equal to that of the object. But it is 1/3 rd.
Answered by
1
Dear student,
● Answer -
u = -40 cm
● Explanation -
# Given -
h2/h1 = 1/3
f = 20 cm
# Solution -
Magnification by comvex lens is given by -
M = h2/h1 = -v/u
1/3 = -v/u
v = -u/3
According to lens formula -
1/f = 1/u + 1/v
1/20 = 1/u - 3/u
u = -40 cm
Therefore, object is 40 cm from optical centre of lens.
Hope this helped...
● Answer -
u = -40 cm
● Explanation -
# Given -
h2/h1 = 1/3
f = 20 cm
# Solution -
Magnification by comvex lens is given by -
M = h2/h1 = -v/u
1/3 = -v/u
v = -u/3
According to lens formula -
1/f = 1/u + 1/v
1/20 = 1/u - 3/u
u = -40 cm
Therefore, object is 40 cm from optical centre of lens.
Hope this helped...
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