Question

A concave lens has focal length 10cm. An object 2. 5cm is placed at 30cm from the lens. Determine the position of object to justify your answer

Answer 1

Given ;
f = -10 cm
u = -2.5 cm
v = ?
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Using mirror formula ;
1/f = 1/v - 1/u
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1/(-10) = 1/v - (1/-2.5)
-1/10 = 1/v + 10/25
-1/10 = 1/v + 2/5

1/v = (-1/10)-(2/5)
1/v = (-1-4)/10
v = 10/-5
v = -2 cm
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Hence the image is formed on a distance of 2 cm in front of the concave lens.