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1.Units, Dimensions and Measurement
medium
Turpentine oil is flowing through a tube of length $l$ and radius $r$. The pressure difference between the two ends of the tube is $P .$ The viscosity of oil is given by $\eta=\frac{P\left(r^{2}-x^{2}\right)}{4 v l}$ where $v$ is the velocity of oil at a distance $x$ from the axis of the tube. The dimensions of $\eta$ are
A
$\left[ {M{L}{T^{ - 1}}} \right]$
B
$\left[ M^0L^0T^0 \right]$
C
$\left[ {M{L^{ - 1}}{T^{ - 1}}} \right]$
D
$\left[ {M{L^{ 2}}{T^{ - 2}}} \right]$
(AIPMT-1993)
Solution
Dimensions of $P=\left[M L^{-1} T^{-2}\right]$
Dimensions of $r=[L]$
Dimensions of $v=\left[L T^{-1}\right]$
Dimensions of $l=[L]$
$\eta=\frac{P\left(r^{2}-x^{2}\right)}{4 v l}$
$=\frac{\left.\left[M L^{-1} T^{-2}\right] L^{2}\right]}{\left[L T^{-1}\right][L]}$
$=\left[M L^{-1} T^{-1}\right]$
Standard 11
Physics