# Measuring the thickness of aluminium leaf

##### Class practical

Using mass, density and area to deduce thickness.

#### Apparatus and materials

*For each student group*

Aluminium leaf, 1 sheet approx 5 cm square

Microbalance (see Technical notes)

Ruler

#### Health & Safety and Technical notes

If students have made microbalances (see the experiment Making a microbalance), the microbalance used in this experiment should be their own. Alternatively, they will require access to a sensitive laboratory balance.

Aluminium leaf is the thinnest sheet of aluminium you can get, beaten out until it is so thin that it flutters in air and you can almost see through it.

#### Procedure

**a** Measure the area of the aluminium leaf.

**b** Weigh the aluminium leaf to find its mass. (It may be necessary to screw the leaf into a ball.)

**c** The density of aluminium is 2710 kg/m^{3} (or 2.710 g/cm^{3}). Calculate the volume of the leaf

(= mass/density). Calculate its thickness (= volume/area).

#### Teaching notes

**1** Put to your students the problem of how the thickness of aluminium leaf can be measured. It is not possible to adopt the procedure of Measuring the thickness of a coin by measuring a pile of aluminium leaves.

Aluminium leaf is much thinner than a sheet of paper and if two pieces are placed together then they stick.

**2** The best procedure is to use a microbalance to find the mass of a known area of aluminium leaf (5 cm^{2}), screwed up into a ball. Given the density of aluminium, the volume of the leaf can be calculated. Since the area is known, the thickness can be estimated. This is an indirect way of measuring the thickness of materials by knowing some other property such as density.

**3** The comparison between the thickness of paper and aluminium leaf will be useful when it is found that paper will stop alpha particles and alumunium leaf does not.

*This experiment was safety-checked in July 2007*