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A lens has a focal length of +20 cm. What type of lens is it?

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Question: A lens has a focal length of +20 cm. What type of lens is it?

Options:

  1. Concave lens
  2. Convex lens
  3. Bifocal lens
  4. Cylindrical lens

Correct Answer: Convex lens

Solution: 

A positive focal length indicates that the lens is a convex lens, which converges light rays.

A lens has a focal length of +20 cm. What type of lens is it?

Practice Questions

Q1
A lens has a focal length of +20 cm. What type of lens is it?
  1. Concave lens
  2. Convex lens
  3. Bifocal lens
  4. Cylindrical lens

Questions & Step-by-Step Solutions

A lens has a focal length of +20 cm. What type of lens is it?
Correct Answer: Convex lens
  • Step 1: Understand what focal length means. Focal length is the distance from the lens to the point where light rays converge or diverge.
  • Step 2: Identify the sign of the focal length. A positive focal length means the lens converges light.
  • Step 3: Know the types of lenses. There are two main types: convex (converging) and concave (diverging).
  • Step 4: Conclude that since the focal length is positive (+20 cm), the lens is a convex lens.
  • Focal Length – The distance from the lens to the focal point, which determines the lens type.
  • Lens Types – Convex lenses have positive focal lengths and converge light, while concave lenses have negative focal lengths and diverge light.
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