a. A candle 6.50cm high is placed in front of a thin converging lens of focal le

Question

a.       A candle 6.50cm high is placed in front of a thin converging lens of focal length 32.5cm. What is the image distance I when the object is placed 94.5 cm in front of the same lens?

                                                               i.      What is the size of the image?

                                                             ii.      Is the image real(R) or virtual (V); upright (U) or inverted (I); larger (L) or smaller (S) or unchanged (UC); in front of the lens (F) or behind the lengs (B)? answer these questions in the order they are posed. (e.g. RILB).

b.      The object is now moved to 49.5 cm in front of the lens, what is the new image distance i?

                                                               i.      What is the new size of the image?

                                                             ii.      Is new image: real or virtual, upright or inverted, larger or smaller, or unchanged. In front of lens or behind?

Explanation / Answer

we know from the relation

1/f = 1/u + 1/v

or 1/v = 1/f - 1/u

where v is image distance,f = 32.5 cm and u = 94.5 cm

Also,

(v/u) = (I/O)

or I = (v/u) x O

where I is size of image and O = 6.50 cm(size of object)

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