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nandithac

when there is liquid the lens acts as a planoconcex lens
with R1=R(RADIUS OF CURVATURE OF CONCEx LENS)
R2=INFINITY(PLANE SURFACE)
THE FOCAL LENGHT OF THE COMBINATION IS GIVEN BY;
1/F=1/f1+1/f2
where f1=f of convex lens
f2=focal lenght of liq lens
1/f2=(n-1){1/R1-1/R2)
=(n-1)/R1
in the problem a=F and b=f1 so solve for f2 and substitute it in the eqn and then u'll get an expression for n

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