Which of the following is NOT a component of a slide projector?

Analyze the question: We need the item that is NOT part of a slide projector.

Concept: A slide projector forms a large, real, inverted image of a small transparent slide on a screen. Its main parts are:

1. Light source (lamp): a bright lamp that illuminates the slide.
2. Concave (spherical) mirror: placed behind the lamp, it reflects light that would otherwise be wasted back toward the slide, which makes the illumination brighter.
3. Condenser lenses: two convex (plano-convex) lenses that gather the light and concentrate it evenly on the slide.
4. Slide holder: holds the slide, which is placed upside down and close to the projection lens.
5. Projection (objective) lens: a convex lens that can be moved back and forth to focus the image. The slide sits just beyond its focal length, so a magnified real image forms.
6. Screen: the surface on which the image is seen. Strictly it is not built into the projector, but it is always part of the projection setup.

Checking each option:

• A. Concave mirror: present, as the reflector behind the lamp.
• B. Condenser: present.
• C. Convex mirror: not used. A convex mirror spreads light out (diverges it), which is the opposite of what a projector needs.
• D. Light source: present.
• E. Screen: part of the projection system.

Answer: The convex mirror is the one that is not a component, so the answer is C.

Exam tip: Remember that a projector needs light to be gathered and focused, so it uses a concave mirror, convex condenser lenses, and a convex projection lens. A convex mirror only diverges light, so it never appears in a projector.