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QJEEM21Ph3de9: JEE Main 2021 Physics - Class 12 JEEM21Ph3de9 Solution: Curved surfaces of a plano-convex lens of refractive index 1…

Curved surfaces of a plano-convex lens of refractive index μ\mu 1 and a plano-concave lens of refractive index μ\mu 2 have equal radius of curvature as shown in figure. Find the ratio of radius of curvature to the focal length of the combined lenses.

JEE Main 2021 (Online) 27th August Evening Shift Physics - Geometrical Optics Question 110 English

Multiple Choice Options

  • A 1μ2−μ1{1 \over {{\mu _2} - {\mu _1}}}
  • B μ1−μ2{\mu _1} - {\mu _2}
  • C 1μ1−μ2{1 \over {{\mu _1} - {\mu _2}}}
  • D μ2−μ1{\mu _2} - {\mu _1}

Step-by-Step Verified Solution

JEE Main 2021 (Online) 27th August Evening Shift Physics - Geometrical Optics Question 110 English Explanation
1f1=(μ1−1)(1R){1 \over {{f_1}}} = ({\mu _1} - 1)\left( {{1 \over R}} \right)

1f2=(μ2−1)(1R){1 \over {{f_2}}} = ({\mu _2} - 1)\left( {{1 \over R}} \right)

1f1+1f2=1feq=(μ1−1)−(μ2−1)R{1 \over {{f_1}}} + {1 \over {{f_2}}} = {1 \over {{f_{eq}}}} = {{({\mu _1} - 1) - ({\mu _2} - 1)} \over R}

1feq=(μ1−μ2)R{1 \over {{f_{eq}}}} = {{({\mu _1} - {\mu _2})} \over R}

Rfeq=(μ1−μ2){R \over {{f_{eq}}}} = ({\mu _1} - {\mu _2})

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