1 cm sample: %T = 70 = 100(I/I0)

I0/I = 1/0.7 = 1.429

A = log(I0/I) = 0.155 = ecl = e c(1) = e c

For length = l'

log(I0/I') = e cl' = 0.155 l'

I0/I' = 100.155 l'

I'/I0 = 0.2 = 10-0.155 l', (i.e., 80% T)

log 0.2 = -0.699 = -0.155 l'

l' = 0/699/0.155 = 4.5 cm
 

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