Question

A transparent photographic slide is placed in front of a converging lens with a focal length of 2.39 cm. An image of the slide is formed 13.2 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.) Incorrect: Your answer is incorrect. Your response differs from the correct answer by more than 10%. Double check your calculations. cm 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.) cm cm

Answer 1

(a) How far is the lens from the slide if the image is real

1/f = 1/p-13.2 - 1/p

1/2.39 = 1/p-13.2 - 1/p

p² - 13.2p + 31.548 = 0

solve this quadratic equation, we get

p = 13.2 +/- sqrt (48.048) / 2

p = 13.2 +/- 6.932 / 2

p = 10.06 cm and p = 3.134 cm

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(b) How far is the lens from the slide if the image is virtual?

p² + 13.2p - 31.548 = 0

solve this quadratic equation, we get

p = -13.2 +/- 17.33 / 2

p = -15.266 cm and p = +2.065 cm

please ignore the negative value.