AskIITians Expert Hari Shankar IITD
Last Activity: 15 Years ago
Density D = mass/Volume
or, D = m/l3
Take log of both sides.
log(D) = log(m) - 3 log(l)
Now, differentiate both sides.
Differential of log(x) is 1/x dx.
x can be anything.
So, here, we have
(1/D) dD =(1/m) dm - 3 (1/l) dl [Because log(1/2) is a constant, and
derivative of any constant is zero]
Now, dK is nothing but delta(K).
So, dK is the error in measurement of K.
dK/K is the relative error in measurement of K.
Percentage error is relative error x 100
Hence,
dK/K = dm/m + 3 dl/l [Note that the minus sign changes to plus, because errors always add up, unlike derivatives]
We are given that dm/m = 0.1% = 0.001
Also, dl/l = 0.3% = 0.003
Therefore, Relative error in measurement of K = dK/K = 0.001 + 3(0.003) = 0.001 + 0.009 = 0.01
Percentage error = 0.01 x 100 = 1 %