Question

The pinhole camera works on the principle of:
A) Reflection of light
B) Refraction of light
C) Rectilinear propagation of light
D) Both A and B.

Answer 1

Hint: A pinhole camera is a simple optical device that works on the principle of light traveling in a straight line. The pinhole camera is a device that does not use a lens or a mirror to form an image. This happens because the light travels in a straight line. The camera forms an inverted image because the straight lines intersect at the pinhole.

Complete solution:
Step 1: First let us understand what reflection, refraction, and rectilinear propagation of light mean.
When a ray incident a smooth and polished surface the surface changes the direction of the ray with the same angle as the ray incident the surface making an angle with the normal. The law of reflection states that, on reflection from a smooth surface, the angle of the reflected ray is equal to the angle of the incident ray. The reflected ray is always in the plane defined by the incident ray and the normal to the surface. This phenomenon can be used to understand the images produced by plane and curved mirrors. We know that in a pinhole camera any lens or mirror is not used. Therefore, the pinhole camera does not work on this principle.
Step 2: When light traveling in one transparent medium encounters a boundary with a second transparent medium, for example, air and glass, a portion of the light is reflected and a portion of the light is transmitted into the second medium. As the transmitted light moves into the second medium, it changes its direction of travel, that is, it is refracted. In the pinhole camera, the light rays travel only in a single medium, not from one medium to another. Therefore, the pinhole camera does not work on this principle.
Step 3: Rectilinear propagation describes the tendency of light to travel in a straight line. Light only deviates from a straight line when the medium it is traveling through changes density. Light does not deviate when traveling through a homogeneous medium, which has the same refractive index throughout. The pinhole camera captures an image only because the light travels in a straight line.

Hence the correct option is Option C.

Note: The shadows occur of the objects because the light travels in a straight line. If we assume for a while that the light does not travel in a straight line, that means, a ray of the light can change its direction without being influenced by any medium or surface then the light will also reach the area where the shadow was supposed to be formed. Similarly, if the rays that are responsible to form an image in a pinhole camera can change their direction then the rays required to form an image may not necessarily reach the screen in the camera and the image will not be formed.