Question

at what distance should an object be placed from a convex lens of focal length 15cm to obtain an image 3 times the size of the object.

Answer 1

Answer:

focal length = f = 15cm

Height of image (hi) = 3 x height of object (hi)

q = 3p (where q is image distance and p is object distace) ; As hi/ho = q/p

p = ??

1/f = 1/p + 1/q (formula)

1/15 = 1/p + 1/3p

1/15 = 4/3p

p = 15(4)/3

p = 20cm

Result: object distance is 20cm from the lens