Question

A camera fitted with a lens of focal length 50 mm is being used to photograph a flower that is 5 cm in diameter. The flower is placed 20 cm in front of the camera lens. (a) At what distance from the film should the lens be adjusted to obtain a sharp image of the flower ?

Answer 1

To find the distance from the film to the lens for a sharp image, use the lens formula 1/f = 1/di + 1/do. With a 50 mm focal length and a flower at 200 mm, the film should be placed 66.7 mm from the lens.

Step-by-step explanation:

To determine at what distance from the film the lens should be adjusted to obtain a sharp image of the flower, we need to use the lens formula: 1/f = 1/di + 1/do, where f is the focal length, di is the image distance (what we want to find), and do is the object distance (distance from the flower to the lens).

For this problem, the camera lens has a focal length (f) of 50.0 mm, and the flower is placed at 20.0 cm (which is 200.0 mm because we need to use the same units for all measurements) in front of the lens. Plugging these values into the lens formula gives:

1/f = 1/di + 1/do
1/50 = 1/di + 1/200

By solving this equation for di, we can find the distance at which the film should be placed from the lens:

1/di = 1/50 - 1/200
1/di = (4 - 1)/200
1/di = 3/200
di = 200/3
di = 66.7 mm

So the lens should be adjusted to 66.7 mm away from the film to obtain a sharp image of the flower.