Question

define focal length and write their formula.​

Answer 1

Answer:

The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power.

Answer 2

Answer:

The distance between the optical centre if a lens and it's focus is called the focal length.

Explanation:

formula

1/f = 1/v - 1/u

where f is the focal length

v is the distance of image from lens

u is the distance of object from lens

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