Expressing Quantities & SI Units Practice Questions

Complete the table to give the name and symbol of the SI unit for each physical quantity.

Physical quantity	Name of SI unit	Symbol of SI unit
mass
electric current
amount of substance

Which of these is not an SI base unit?

• A second
• B newton
• C kelvin
• D metre

Complete the table.

Prefix	Symbol	Multiplying factor as a power of ten
mega	M
centi		$10^{-2}$
	n	$10^{-9}$

A student measures the thickness of a glass block as $250\ \mathrm{mm}$.

Convert this thickness to metres.

thickness = .............................................................. m

Write $0.000\,072\ \mathrm{m}$ in standard form.

.............................................................. m

Write $3.4 \times 10^{6}\ \mathrm{Hz}$ as an ordinary number.

.............................................................. Hz

A student says that an energy transfer of $750\ \mathrm{kJ}$ is greater than an energy transfer of $0.8\ \mathrm{MJ}$.

State whether the student is correct. Give a reason for your answer.

A ferry crossing takes $1$ hour and $25$ minutes.

Calculate this time in seconds.

time = .............................................................. s

A camera shutter is open for $4000\ \mathrm{\mu s}$.

Calculate this time in seconds. Give your answer in standard form.

time = .............................................................. s

Complete the table to give the name of the derived SI unit for each physical quantity.

Physical quantity	Name of SI unit
frequency
pressure
electric charge

Potential difference is measured in volts (V).

Which of these is also a unit for potential difference?

• A $\mathrm{C/J}$
• B $\mathrm{J/C}$
• C $\mathrm{J/A}$
• D $\mathrm{A/C}$

Show that a density of $2.7\ \mathrm{g/cm^3}$ is the same as a density of $2700\ \mathrm{kg/m^3}$.

A sample of brass has a density of $8.5 \times 10^{3}\ \mathrm{kg/m^3}$.

State which is the denser material, aluminium or brass.

Calculate the mean current, in mA, to an appropriate number of significant figures.

mean current = .............................................................. mA

Convert the mean current to amperes. Give your answer in standard form.

mean current = .............................................................. A

Show that the volume of the cube is $8 \times 10^{-6}\ \mathrm{m^3}$.

Calculate the density of the metal in $\mathrm{kg/m^3}$.

Give your answer in standard form to 2 significant figures.

$$\text{density} = \frac{\text{mass}}{\text{volume}}$$

density = .............................................................. $\mathrm{kg/m^3}$

The student writes the density as $6750\ \mathrm{kg/m^3}$.

Explain why it is not appropriate to give the density to this number of significant figures.