The use of lenses is Not applicable in the

1. Analyze the question We are asked which device does NOT use lenses (or where lenses are not applicable). We check each option.

2. Explain the concept

• A lens refracts light to form images.
• A plane mirror reflects light and does not need a lens.

3. Check each option

• A. Projector: uses a converging (convex) lens to form a magnified image on the screen. Lenses are used.
• B. Human eye: has a convex lens that focuses light onto the retina. Lenses are used.
• C. Periscope: in its simple form, it uses two plane mirrors (or right-angled prisms) set parallel at 45° to the tube. Light is reflected twice, so the observer sees over obstacles. No lens is needed for its basic action.
• D. Telescope: has an objective lens and an eyepiece lens (a refracting telescope). Even a reflecting telescope uses an eyepiece lens. Lenses are used.

4. Answer The simple periscope works purely by reflection from plane mirrors, so lenses are not applicable there.

Correct option: C. periscope

5. Exam tip Remember: Periscope = Plane mirrors (reflection). Both start with "P". When you see "periscope" in JAMB, think "mirrors or prisms, not lenses".