The focal length of a lens is given by:
(Assume terms have standard meanings)

f = \frac{u - v}{u v}

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f = \frac{u v}{u - v}

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f = \frac{u + v}{u v}

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f = \frac{u v}{u + v}

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Solution

The correct option is B $f = \frac{u v}{u - v}$
According to Lens formula:
$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
where:
$f :$ Focal length of the lens
$v :$ Image distance
$u :$ Object distance

Rearranging the terms, we get:
$f = \frac{u v}{u - v}$

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Assume terms have their standard meanings.

Q. When two thin lenses are kept in contact, prove that their combined or effective focal length F is given by

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where the terms have their usual meaning.

Define the term focal length of a lens.

Question 8
Which of the following statements is true?
(a) A convex lens has 4 dioptre power having a focal length 0.25 m.
(b) A convex lens has -4 dioptre power having a focal length -0.25 m.
(c) A concave lens has 4 dioptre power having a focal length 0.25 m.
(d) A concave lens has 4 dioptre power having a focal length -0.25 m.

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The focal length of a lens is given by: (Assume terms have standard meanings)

The correct option is B f=uvu−vAccording to Lens formula: 1f=1v−1u where: f: Focal length of the lens v: Image distance u: Object distance Rearranging the terms, we get: f=uvu−v

The focal length of a lens is given by:
(Assume terms have standard meanings)

The correct option is B $f = \frac{u v}{u - v}$
According to Lens formula:
$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
where:
$f :$ Focal length of the lens
$v :$ Image distance
$u :$ Object distance

Rearranging the terms, we get:
$f = \frac{u v}{u - v}$