zaro

Why is a concave lens called a diverging lens class 10?

Published in Lens Optics 3 mins read

A concave lens is called a diverging lens because it causes parallel rays of light to spread out, or "diverge," after passing through it.

Understanding Concave Lenses and Light Divergence

Fundamentally, a concave lens is known as a diverging lens because of its unique interaction with light: if parallel rays of light fall on a concave lens, they diverge as they pass through the lens, spreading out and never meeting at a single real point. This inherent characteristic of causing light rays to spread makes "diverging lens" an accurate and descriptive term.

A concave lens is thinner at its center and thicker at its edges. This specific curvature dictates how it interacts with incident light rays. Unlike a convex lens, which converges light to a real focal point, a concave lens always spreads light outward.

How Concave Lenses Diverge Light

The Principle of Divergence

When light rays parallel to the principal axis strike a concave lens, they refract outwards, away from the principal axis. These refracted rays appear to originate from a single point on the principal axis on the same side as the incident light. This point is known as the principal focus (F), which is always a virtual focus for a concave lens. This means the rays themselves do not actually pass through this point; they only appear to diverge from it.

Key Characteristics of Divergence

  • Spreading Effect: The primary function is to spread out light rays.
  • Virtual Focus: Light rays, after refraction, appear to come from a virtual focal point located on the same side as the incoming light.
  • Image Formation: Concave lenses always form virtual, erect, and diminished images, regardless of the object's position. This is a direct consequence of their diverging nature.

Concave vs. Convex: A Quick Comparison

Understanding the difference between concave (diverging) and convex (converging) lenses is crucial:

Feature Concave Lens (Diverging) Convex Lens (Converging)
Shape Thinner in the middle, thicker at the edges Thicker in the middle, thinner at the edges
Light Behavior Spreads out parallel light rays Brings parallel light rays together at a point
Focal Point Virtual focus (light appears to diverge from it) Real focus (light actually converges at this point)
Image Type Always virtual, erect, and diminished Can be real or virtual, erect or inverted, magnified or diminished
Primary Use Spreading light, correcting nearsightedness (myopia) Focusing light, magnifying, correcting farsightedness (hyperopia)

For further exploration of lens properties and ray diagrams, you can consult reliable educational resources such as Khan Academy or physics textbooks.

Practical Applications of Diverging Lenses

The unique light-diverging property of concave lenses makes them indispensable in various applications:

  • Eyeglasses for Myopia (Nearsightedness): Concave lenses are used to correct nearsightedness by diverging light rays before they enter the eye, allowing them to focus correctly on the retina.
  • Peepholes: The wide-angle view provided by a concave lens in a peephole allows you to see a broader area outside the door.
  • Flashlights: While convex lenses are used to focus light, some flashlights might use a concave lens in combination with others to achieve a broader, more diffused beam.
  • Telescopes (Galilean Telescopes): Concave lenses are used as eyepieces in Galilean telescopes to produce an erect image.

In summary, a concave lens is fundamentally termed a diverging lens because of its intrinsic ability to spread out incident parallel light rays rather than converge them, forming a virtual focus and always producing virtual, upright, and diminished images.