# The water circuit: modelling current and potential difference

##### Demonstration

Current can be modelled by the flow of water; potential difference corresponds to water pressure.

#### Apparatus and materials

Water circuit board

Power supply, low voltage, variable (to match pump)

Fluorescein solution or methyl orange solution (see CLEAPSS Recipe Cards)

Pressure gauge

Small piece of cork

#### Procedure

a Set up the water circuit board vertically. Connect the electric motor, which drives the water pump, to the terminals of the low voltage supply. (Ensure that the supply is matched to the pump: correct voltage, DC or AC.)

b Fill the tubes with water: a little fluorescein or a few drops of methyl orange can be added to make the water more clearly visible. The water is conveniently poured in at the funnel.

c The pump will drive water round the circuit of glass tubing attached to the board, the pressure being dependent on the voltage applied to the motor.

d At one point, the tube divides. The two sections represent different resistances: one tube has a much finer bore than the other.

e Clips enable one or other or both sections to be opened at once: thus the effect on the current of different 'resistances' can be seen.

f Where there is a break in the circuit, the funnel catches the water flowing down from the tube above. The rate of flow of water is apparent and this indicates the current. Alternatively, if there is a pool of water in the funnel, the faster the flow of water the more rapid the swirling motion in the funnel. A small piece of cork floating on the water in the funnel acts as an indicator of the rate of swirling, which thus shows the current.

g In this demonstration, do not use the pressure gauge at first. Add it later. It consists of a U-tube connected as illustrated and filled with coloured water. This enables you to demonstrate the change in current with pressure (voltage).

#### Teaching notes

1 The water circuit is a demonstration which can be referred to at many points in a course of elementary electricity teaching.

This experiment was safety-checked in January 2007