A transparent photographic slide is placed in front of a converging lens with a

Question

A transparent photographic slide is placed in front of a converging lens with a focal length of 2.45 cm. An image of the slide is formed 15.0 cm from the slide.

(a) How far is the lens from the slide if the image is real? (Enter your answers from smallest to largest starting with the first answer blank. Enter NONE in any remaining answer blanks.)

(b) How far is the lens from the slide if the image is virtual? (Enter your answers from smallest to largest starting with the first answer blank. Enter NONE in any remaining answer blanks.)

Explanation / Answer

a) image is real

so m is negative

so v is positive

v = +15 cm

f = +2.45cm

1/f = 1/u + 1/v

1/2.45 = 1/u + 1/15

u = 2.928 cm

b) image is virtual

so m is positive

m = -v/u since m is positive

so v is negative

v = -15 cm

f = +2.45cm

1/f = 1/u + 1/v

1/2.45 = 1/u + 1/-15

u = 2.106 cm

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