You have a lens with a focal length that has a magnitude of 56 cm. When you plac

Question

You have a lens with a focal length that has a magnitude of 56 cm. When you place an object in front of the lens, you observe that the lens creates an image of the object, such that the object is 3 times larger than the image. What is the object distance? (a) It turns out that there are two possible solutions. The one in which the image is real is ... (b) The one in which the image is virtual is ... (c) Starting from either one of these locations, if you then move the object a little bit toward the lens, the image will ... (select all that apply). get smaller in size get larger in size stay the same size move dos o the lens move farther from the lens stay the same distance from the lens as far as distance from the lens goes, it actually depends which of the two object distances we start from

Explanation / Answer

f = 56 cm ;

m = 3

We know that,

m = -(-i)/o = 3

i = 3o

from lens eqn we know that

1/f = 1/i + 1/o

1/56 = 1/3o + 1/o = 1/o(1/3 + 1) = 4/3o

o = 4 x 56/3 = 74.67 cm

Hence, o = 74.67 cm

b)m = -i/o = 3

i = -3o

1/56 = 1/o(1 - 1/3) = 2/3o

o = 2 x 56/3 = 37.33 cm

Hence, o = 37.33 cm

c)The image will get smaller in size, as

i = 3o ;as o decreases i also decreases.

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