Edexcel A-Level Physics Units in Calculations

Review units in calculations in Edexcel A-Level Physics through SI base-unit derivations, derived quantities and unit checks from data.

Exam points

identify SI base units for derived quantities such as farads, watts and tesla
show formula units by substituting base or derived units into calculation expressions
check whether table units are consistent by calculating values such as current from R = V/I

[Maximum number: 2]

A student investigated the flow of water through a horizontal pipe using the apparatus shown.

Figure for Question C.0.1—Units in calculations question 1 — Edexcel A-Level Physics A2

The mass M of water leaving the pipe in a time t is given by the formula

M=\frac{\pi \rho P r^{4} t}{8 \eta L}

where
$\rho=$ density of water
P= pressure difference between the ends of the pipe
r= internal radius of the pipe
$\eta=$ viscosity of water
L= distance between digital pressure gauges

Show that the formula gives the unit for $\eta$ as $\mathrm{N\,s\,m^{-2}}$ .

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C.0.1—Units in calculations question 1