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Two thin lenses of power 3D and -2D areaced in contact then power and focal length of the lens combination is (A) 2D, +100 cm(B)+1D,+100 cm(C) +5D,+20 cm(D) +1D,-100 cm |
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Answer» Power of two lenses are 3D and -2DTo Find◈ Power & the focal length?SolutionConceptWe shall FIRST find the power of the combined and then use the FORMULA P = 1/f to find the focal length and hence solved!!━━━━━━━━So we know that,P = P¹+P²P¹ = +3DP² = -2DSubstituting the given values,➝ P = P¹+P²➝ P = 3+(-2)➝ P = +1DNow the focal length can be found with the help of,P = 1/fP = +1DSubstituting the values,➳ P = 1/f➳ f = 1/P➳ f = 1/1➳ f = 1 MSO on converting to cm,»» 1 m = 100 cm∴ Power is +1D & Focal Length is +100 cm (Option B)━━━━━━━━━━━━━━━━ |
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