Lens which is thicker in the middle than at the edges are called

RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

General Knowledge

Easy

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Explanation

A convex lens is defined by its physical shape: it is thicker at the center and tapers to become thinner at its edges.
This specific curvature causes parallel rays of light to refract (bend) inwards as they pass through the lens.
The key function of a convex lens is to converge light to a single point, known as the focal point. This property is essential for magnification and correcting certain vision defects.

Option A: A concave lens has the opposite shape; it is thinner in the middle and thicker at the edges.
Option B: A biconcave lens is a specific type of concave lens where both surfaces curve inwards. It is also thinner in the middle and diverges light.
Option D: A plane mirror is a reflective surface, not a lens. It works by reflection, not refraction (the bending of light as it passes through a medium).

Visual 1: Diagram - A clear diagram comparing the cross-sectional shapes of a convex lens (bulging center) and a concave lens (caved-in center).
Visual 2: Ray Diagram - An illustration showing parallel light rays entering a convex lens and converging to a single focal point after passing through it.
Visual 3: Ray Diagram - An illustration showing parallel light rays entering a concave lens and diverging (spreading out) after passing through it.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain This question tests the basic understanding of the physical properties and definitions of different types of optical lenses as background academic context rather than a clinical decision trigger.
The principles of lenses are fundamental to ophthalmology and optometry. Nurses often care for patients with vision problems that are corrected using these principles.
Convex lenses are used in eyeglasses to correct hyperopia (farsightedness), a condition where the eye focuses images behind the retina. The convex lens adds focusing power to converge light correctly onto the retina.
Concave lenses are used to correct myopia (nearsightedness), where the eye focuses images in front of the retina. The concave lens diverges light slightly before it enters the eye, effectively moving the focal point back onto the retina.

How to Approach the Question

First, identify the core of the question. It's asking for the name of a lens based on its physical shape.
Focus on the key descriptive phrase: 'thicker in the middle than at the edges'.
Mentally recall or visualize the definitions of the different options. A 'convex' surface bulges outwards, while a 'concave' surface caves inwards.
Match the description to the definition. A lens that is thicker in the middle has a bulging, or convex, shape.
Evaluate the other options to confirm your choice. A concave lens is the opposite. A plane mirror is not a lens and works by reflection.
Select 'convex lens' as the term that directly matches the physical description provided.

Concept Tested & Keywords

Concept Tested: This question tests the basic understanding of the physical properties and definitions of different types of optical lenses.
Stem keywords: Lens, thicker in the middle, thinner at the edges
Lead-in keywords: are called

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