A 6-cm-high candle is placed in front of a converging lens with a focal length of magnitude 30 cm.If the image distance is +50 cm,then find the object distance to the lens.
A)75 cm
B)50 cm
C)60 cm
D)80 cm
E)None of these is correct.

Question

Quizplus · Accepted Answer

We can use the thin lens equation:

1/f = 1/o + 1/i

where f is the focal length of the lens, o is the object distance, and i is the image distance.

Plugging in the given values:

1/30 = 1/o + 1/50

Solving for o:

1/o = 1/50 - 1/30

1/o = (3 - 5)/150

1/o = -2/150

o = -75 cm

We have a negative value for o, which means that the candle is located on the opposite side of the lens from the side where the image is formed. Taking the magnitude of this gives:

|o| = 75 cm

So the object distance to the lens is 75 cm.

A 6-Cm-High Candle Is Placed in Front of a Converging