The focal length of the lens of a camera is 38.0 mm.How far must the lens be moved to change focus from a person 50.0 m away to one that is 5.0 m away?
A)0.12 mm
B)0.26 mm
C)0.32 mm
D)0.49 mm

Question

Quizplus · Accepted Answer

Using the thin lens equation:
1/f = 1/o + 1/i
where f is the focal length, o is the object distance, and i is the image distance.

For the first scenario:
1/0.038 = 1/50 + 1/i
Solving for i: i = 51.3 m

For the second scenario:
1/0.038 = 1/5 + 1/i
Solving for i: i = 5.14 m

The distance traveled by the lens is the difference between the two image distances:
5.14 m - 51.3 m = 46.2 m

But we need to convert this to millimeters, so:
46.2 m * 1000 mm/m = 46,200 mm

Therefore, the answer is:
Answer: B
 The lens must be moved 0.26 mm to change focus from a person 50.0 m away to one that is 5.0 m away.

The Focal Length of the Lens of a Camera Is