preproom.org

CLOSE WINDOW

PRINTER FRIENDLY WORKSHOP

Electroscope
(AKA: Gold-leaf Electroscope)


Difficulty Level: 1 very simple

Parts & Tools

  • Glass or plastic jar with screw lid
  • Thin steel rod (approx 3mm dia.)
  • Gold leaf (Dutch metal)
  • Aluminium foil
  • Hand drill
  • Drill bit (same diameter as steel rod)
  • Glue gun and glue
  • Wire cutters (to trim the rod)

Instructions

Electroscopes or 'gold-leaf' electroscopes as they are sometimes known are devices which measure electrical charge (static electricity). They usually consist of a metal box with glass windows and a charge plate on top. Inside the box is a rod with a small piece of gold leaf (Dutch metal is often used because it is much cheaper). When an electrostatically charged material (a polycarbonate rod for example) is brought near the top of an electroscope, the charge travels down the metal part (electrode) and charges the gold leaf. In the case of the two leaf electroscope, both leaves become equally charged and repel each other.

More information regarding electroscopes can be found in our Equipment section.

This guide shows how to make a simple electroscope which works in the same way as commercial devices. Instead of a charge plate, aluminium foil is used but all the other parts are similar to those found in more expensive models and can be used in the classroom just as effectively.

Firstly you will need to find a glass or plastic jar to use as the case of the device. Smaller jars work better and glass jars will work better than plastic ones although all types will work to some extent. The lid needs to be removable.

Fig 1: Jar and steel rod
Fig 1: Jar and steel rod

Fig 1 shows the jar and steel rod. The rod should be bent at a right angle near the bottom, leaving approximately 3-4cm for the gold leaf to rest upon. A hole should be drilled into the lid of the jar nearer one side. This will enable the gold leaf to be central to the jar. It is important that the gold leaf does not touch the sides of the jar so use the bent rod as a drilling guide. The hole should be the same diameter as the rod or slightly smaller.

Fig 2: Gold leaf folded over the rod
Fig 2: Gold leaf folded over the rod

Fig 2 shows how the gold leaf is folded over the bent part of the rod. A strip of leaf should be cut that is approximately 6cm long and 1cm wide. This should gently folded in half and rested over the bent part of the bar leaving 3cm of leaf over each side.

Fig 3: Insert rod and leaf into the jar
Fig 3: Insert rod and leaf into the jar

The rod and leaf should be inserted into the jar as in fig 3. Glue the rod in place if you need to. Ensure the gold leaf or rod is not touching the inside of the jar at any point.

Cut a piece of aluminium foil and roll it into a ball. This will act at the charge plate. Make sure the ball is scrunched as tightly as possible and secure to the top of the rod. The ball should be only a few centimetres from the top of the jar so you may need to trim the rod accordingly.

Fig 4: Ready for testing
Fig 4: Ready for testing

The electroscope should now be ready to test (see fig 4).

Charge a balloon by rubbing it on your hair or a duster until it is charged. Bring the balloon near the aluminium ball and the two parts of the gold leaf should separate slightly.

The effectiveness of electroscopes can depend on atmospheric conditions and so on damp days the leaf may not separate as easily.

Electroscopes can be purchased from suppliers for around 30-50. This working model should cost you approximately 50p assuming you have a spare glass jar. Dutch metal can be purchased in books of 50-100 leaves, enough to make thousands of electroscopes! Steel rods can be purchased cheaply from most suppliers or scrounged from your technology department for free.

On a class set of 15 electroscopes, by using this guide you could save yourself 600.

Disclaimer

Before attempting any of the construction projects featured on this website, ensure you have, and know how to use, the appropriate tools, components and safety equipment and are competent to undertake the project. These guides are for information only and we hold no responsibility for any accidents, injuries or damage caused by the use or misuse of any equipment, project or information contained within this website. In short - use common sense and stay safe!