Flowing fluids can become charged

Demonstration

To illustrate the dangers associated with transferring fuel.

Apparatus and Materials

• Small polythene funnel
• 50 cm polythene tubing
• 50 cm of copper tubing
• polystyrene beads (e.g. as used in bean bags)
• Small beaker
• Small calorimeter can
• Coulombmeter or gold leaf electroscope
• Clamp stand

Health & Safety and Technical Notes

Read our standard health & safety guidance

There is a risk of slipping if the spheres fall onto the floor.

If possible stand the whole apparatus on a tray to contain any spilled polystyrene spheres.

Procedure

1. Assemble the apparatus as in the diagram:
2. Place the calorimeter on top of the coulombmeter or electroscope
3. Clamp the tube and funnel above the calorimeter with the end of the tube just at the centre of the calorimeter.
4. Pour polystyrene spheres into the funnel so they flow down into the calorimeter.
5. The charge on the spheres will cause the gold leaf to rise, or produce a reading on the coulombmeter.

Teaching Notes

• The polystyrene spheres, which are insulators, become charged by friction as they tumble down the insulating tubing. It is important that this tubing is polythene and not PVC. This illustrates how insulating liquids such as aviation fuel can become charged as they flow through pipes.
• Repeat the demonstration with copper tubing connected to the calorimeter, to show that any charge developed is now safely discharged.

This experiment was submitted by Sylvia Bell, Head of Physics at Nottingham High School for Girls.