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Why is film placed in a light sensitive box which is painted black from the inside?
(A) To reduce external interference
(B) To reduce reflections of light within the camera
(C) To protect the film
(D) All of these

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Last updated date: 14th Jun 2024
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Answer
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Hint A black surface absorbs most of the visible light incident on it. Light proof boxes block out all light, and do not admit any light which is incident on it. As a result it reduces interference from outside.

Complete step by step answer
Films, in general, are photosensitive materials that is to say they react considerably to the faintest direct (or reflected) light striking their surface. Technically, they need to be so in order to capture and retain the image of an object. However, this same property of it makes it susceptible to other unwanted rays of light that may be incident on its surface.
For this reason, light proof boxes are used in housing a photographic film to prevent unnecessary outside light from other angles to become incident on the surface. Also light proof boxes can protect the film from heat damage that may be caused by extreme exposure to sources emitting large amounts of heat such as fire or notably, the sun.
However cameras, as it is their function can still allow a considerable amount of light to pass into the box through the aperture. Ideally, all light rays passing through the aperture, are to be focused on the film to produce a clear image. However, this is not so as some of the light may not get focused on the film and hence strike the camera surface. This is why they are made black so those light rays are absorbed by the walls rather than reflected around until they strike the film. This would cause blurred images.
Hence we conclude that the light proof box is used for the purposes given in the options.
Thus, the correct answer is D.

Note
For clarity, a reason some of the light may not be incident on the film is because, the films are placed at the focal length of the lens which is where light from infinity (i.e. very far relative to the width of camera) are to be focused, however light from nearby sources, may converge behind the film and thus strike the box.