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 2.65 cm. An image of the slide is formed 12.4 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.) -2.18 Incorrect: Your answer is incorrect. The response you submitted has the wrong sign. cm 3.37 Incorrect: Your answer is incorrect. Your response differs from the correct answer by more than 10%. Double check your calculations. cm (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) f = 2.65 cm, v = u + 12.4

From lens formulae 1/v - 1/u = 1/2.65

1/(u + 12.4) - 1/u = 1/2.65

u2 + 12.4 u + 32.86 = 0

u = -3.84 cm, u = -8.56 cm

Nearest possible distance = 3.84 cm. Farther distance = 8.56 cm

b) From lens formulae 1/v - 1/u = 1/2.65

1/(u - 12.4) - 1/u = 1/2.65

u2 - 12.4 u - 32.86 = 0

u = -2.24 cm

Nearest possible distance = 2.24 cm. Farther distance = none

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