//chapter8,Example8_3,pg 181

n=10

D10=0.5

lam=5000*10^-8

R=(D10^2)/(4*n*lam)

D50=sqrt(4*50*R*lam)

r50=D50/2

printf("radius of 50th dark ring\n")

printf("r50=%.2f cm",r50)