हिंदी

Mirror Equation/Formula

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Topics

  • Introduction
  • Stepwise Derivation of the Mirror Formula

Introduction:

In spherical mirrors, three primary distances are considered:

  • Object Distance (u): The distance of the object from the pole of the mirror.
  • Image Distance (v): The distance of the image from the pole of the mirror.
  • Focal Length (f): The distance of the principal focus from the pole of the mirror.

These quantities are related by a mathematical expression known as the mirror formula:

`"1"/"v"`+`"1"/"u"`=`"1"/"f"`

Stepwise Derivation of the Mirror Formula:

The derivation of the mirror equation establishes the relationship between the object distance (u), image distance (), and focal length (). In the given setup, the two right-angled triangles A′B′F and MPF are identified as similar triangles.

The triangles B′A′F and PMF are similar because they share common angles. Using the property of similar triangles:

`"B'A'"/"PM"`=`"B'F"/"FP"`

Substituting PM=AB into the equation:

`"B'A'"/"BA"`=`"B'F"/"FP"` .............(i)

∠APB = ∠A'PB

△A'B'P' ∼ △AB'P

`"B'A'"/"BA"` = `"B'P"/"BP"` ............(ii)

By comparing equation (i) and (ii), we get

`"B'F"/"FP"`= `"B'P-FP"/"FP"` = `"B'P"/"BP"`

B'P = -ν (image distance),

FP = -f  (focal length),

BP = -u (object distance).

Substituting these values:

`"-ν+f"/"-f"` = `"-ν"/"-u"`

`"ν-f"/"f"` = `"ν"/"u"`

On further solving, we get

`"1"/"v"`+`"1"/"u"`=`"1"/"f"`

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