Question

Which mirror is used in movie projectors?
A. convex mirror
B. concave mirror
C. plane mirror
D. parabolic mirror

Answer 1

Hint: Projector are devices which can project the images on surfaces. Usually, the surfaces are plain white screens, also called the projection screen. These can be seen in the movie theaters, or in auditoriums. However due to the emergence of technology they use lasers now.

Complete answer:
In the 1100’s when people had a few very basic ideas of the light. In 1275 a French author Jean de Meun, gave a theory that the artists either used a refractive lens or a concave mirror to project their ideas on a canvas board for drawing.

Concave mirrors or also known as the diverging mirrors reflect the light outwards. The concave mirrors created virtual images which could not be captured on a screen. But, they noticed that the reflected image of a concave mirror, which is a kind of a curved mirror, could give a real inverted image of the object at the focal point of the mirror. They used this to construct the parabolic reflectors which had a pair of two opposing concave mirrors; with a small opening in the centre this created a 3D like illusion. They also observed that the smaller the distance between the mirror and the object, the larger is the image formed.

Hence, concave mirrors are used in projectors.

So, the correct answer is “Option B”.

Note:
In the modern days the projectors use lenses or lasers to project on the screens. However, there are also virtual retinal displays, which project the image directly on the retina of the eyes, where the retina acts as a screen instead of any external screens.