Question

What principle of projection work in the case of overhead projectors?

• A. Indirect
• B. Direct
• C. Reflected
• D. Both Indirect and Direct

Hint:

Exam Tip:
Opaque Projector: Uses reflected light (from a non-transparent image).
Overhead Projector: Uses transmitted/reflected light (through a transparent sheet, reflected by a mirror).
Slide/Film Projector: Uses transmitted light.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question tests knowledge of the working principles of different types of projectors and audio-visual equipment.

Step 2: Analyzing Different Projection Principles:
There are three main principles of projection used in AV equipment:
• Direct Projection: The image is projected directly onto a screen.
_ _ _ _ Example: Film projectors, slide projectors.
• Indirect Projection: The image is reflected off a mirror or other surface before reaching the screen.
_ _ _ _ Example: Overhead projectors, episcopes.
• Reflected Projection (Opaque Projection): The light is reflected off the surface of a non-transparent object.
_ _ _ _ Example: Opaque projectors.

Step 3: Analyzing the Overhead Projector (OHP):
An overhead projector works on the principle of reflected/refracted light.

• A bright light shines through the transparent sheet (or transparency).
• The light is then reflected by a mirror and projected onto the screen.
• The image is formed by light passing through the transparency and being reflected by the mirror onto the screen.
• This is a combination of refraction (light passing through the transparency) and reflection (the mirror). Technically, an OHP uses a combination of refraction and reflection.
However, in many classifications, it is considered to work on the principle of reflected projection because the light is reflected by a mirror.
The most appropriate answer among the options is Reflected.

Step 4: Final Answer:
Overhead projectors work on the principle of Reflected projection. Therefore, option (C) is correct.