AB=6cm
r=3cm
OA2=OP2+PA2
R2=(R−t)2+r2
R2=R2+t2−2Rt+r2
2Rt=t2+r2
R=2tt2+r2=2×0⋅3(0⋅3)2+(3)2
R≈2tr2=2×0⋅3(3)2=0⋅69=690=15cm
Use f1=(μ−1)(R11−R21)
f1=(1.5−1)(151)=301
f=30cm
Diameter of a plano - convex lens is 6cm and thickness at the centre is 3mm. If the speed of light in the material of lens is 2×108ms−1, the focal length of the lens is:
Held on 7 Apr 2013 · Verified 6 Jul 2026.
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