Power of a Lens in Physics
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Questions and Answers

What is the unit of power of a lens?

  • Dioptre (correct)
  • Metre
  • Centimetre
  • Millimetre

    • What is the power of a lens a measure of?

  • Its ability to reflect light
  • Its ability to magnify an object
  • Its ability to converge or diverge light rays (correct)
  • Its ability to absorb light

    • What is the formula to calculate the power of a lens?

  • P = 1 / f (correct)
  • P = f^2
  • P = f
  • P = 1 / f^2

    • What is the sign convention for the power of a lens?

    <p>A converging lens has a positive power</p> Signup and view all the answers

    When two or more lenses are combined, how do their powers behave?

    <p>Their powers add algebraically</p> Signup and view all the answers

    What is the total power of a combination of a convex lens with a power of +2D and a concave lens with a power of -3D?

    <p>-1D</p> Signup and view all the answers

    Study Notes

    Power of a Lens

    Definition

    • The power of a lens is a measure of its ability to converge or diverge light rays.
    • It is defined as the reciprocal of the focal length of the lens.

    Units

    • The unit of power of a lens is dioptre (D).
    • 1 dioptre is equivalent to a focal length of 1 metre.

    Formula

    • The power of a lens (P) can be calculated using the formula:
    P = 1 / f

    where f is the focal length of the lens in metres.

    Sign Convention

    • A converging lens (convex lens) has a positive power.
    • A diverging lens (concave lens) has a negative power.

    Lens Combinations

    • When two or more lenses are combined, their powers add algebraically.
    • The total power of the combination is the sum of the individual powers.

    Example

    • A convex lens has a power of +2D and a concave lens has a power of -3D. The total power of the combination is:
    P_total = +2D - 3D = -1D

    The combination behaves like a diverging lens.

    Power of a Lens

    • The power of a lens measures its ability to converge or diverge light rays.
    • It is defined as the reciprocal of the focal length of the lens.

    Units

    • The unit of power of a lens is dioptre (D).
    • 1 dioptre is equivalent to a focal length of 1 metre.

    Formula

    • The power of a lens (P) is calculated using the formula: P = 1 / f, where f is the focal length of the lens in metres.

    Sign Convention

    • Converging lenses (convex lenses) have positive power.
    • Diverging lenses (concave lenses) have negative power.

    Lens Combinations

    • When combining two or more lenses, their powers add algebraically.
    • The total power of the combination is the sum of the individual powers.
    • The total power determines the behaviour of the combination, whether converging or diverging.

    Example of Lens Combination

    • A convex lens with a power of +2D combined with a concave lens with a power of -3D has a total power of -1D.
    • The combination behaves like a diverging lens.

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    Description

    Learn about the power of a lens, its definition, units, formula, and sign convention. Understand how to calculate the power of a lens and its application in physics.

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