1) A lighted candle is placed 38.0 cm in front of a diverging lens. The light pa

Question

1) A lighted candle is placed 38.0 cm in front of a diverging lens. The light passes through the diverging lens and on to a converging lens of focal length 12.0 cm that is 9.0 cm from the diverging lens. The final image is real, inverted, and 41.0 cm beyond the converging lens. Find the focal length of the diverging lens.

2) A convex (converging) lens produces a real, inverted image of an object that is magnified 2.30 times when the object is 43.0 cm from the lens. What is the focal length of the lens?

Explanation / Answer

for converging lens

focal length f = 12 cm

image distance v from converging lens 41 -9 = 32 cm

using 1/f = 1/u + 1/v

1/u = 1/12 - 1/32

u = 19.2 cm

this will be the image distance from diverging lens

so for diverging lens

u = 38 cm

v = 19.2 cm

so

1/f = 1/38 + 1/19.2

f = 12.75 cm

------------------------------------------------

2.

magnification m = -v/u

m = -v/43 = 2.3

v = 43* 2.3 = 98.9 cm

so

1/f = 1/43 -1./98.9

f = 76.7 cm

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