Q50 / 116 · NTA Abhyas (JEE Main) 2020 · Physics · Ray Optics

Convex lens made up of glass μg = 1.5 and radius of curvature R is dipped into the water. Its focal length will be (Refractive index of water = 43)

  • Correct answer
    A
    4R
  • B
    2R
  • C
    R
  • D
    R2

Solution

Here, μg=1.5=32, μw ᷿=43

R1=R,⇒R2=-R

From, lens maker's formula

1f=μ-11R1-1R2where μ=μLμM

∴1faₐ=μgμaₐ-11R-1-R



⇒1fa=1R

Also

1fw ᷿=μgμwₐ-11R-1-R



Or  1fw=14R

Or fw ᷿=4R

Hence, the correct answer is option: 'A'.

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