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Geometrical Optics question

2012 · Q141
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Geometrical Optics question

2012 · Q141

NEETPhysicsGeometrical OpticsMCQ+4 / −1
When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index
  1. A
    equal to that of glass
  2. B
    less than one
  3. C
    greater than that of glass
  4. D
    less than that of glass
View written solutionFree

Correct answer: A

According to lens maker's formula

1f=(μgμL−1)(1R1−1R2){1 \over f} = \left( {{{{\mu _g}} \over {{\mu _L}}} - 1} \right)\left( {{1 \over {{R_1}}} - {1 \over {{R_2}}}} \right)f1​=(μL​μg​​−1)(R1​1​−R2​1​)

As the biconvex lens dipped in a liquid acts as a plane sheet of glass, therefore

f = ∞\infty ∞ ⇒\Rightarrow⇒ 1f=0{1 \over f} = 0f1​=0

∴\therefore∴ μgμL−1=0{{{{\mu _g}} \over {{\mu _L}}} - 1 = 0}μL​μg​​−1=0

⇒\Rightarrow⇒ μg=μL{{\mu _g} = {\mu _L}}μg​=μL​

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