This is an instrument for detecting and measuring static electricity or voltage. A metal disc is connected to a narrow metal plate and a thin piece of gold leaf is fixed to the plate. The whole of this part of the electroscope is insulated from the body of the instrument. A glass front prevents air draughts but allows you to watch the behaviour of the leaf. When a charge is put on the disc at the top it spreads down to the plate and leaf.
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Teaching Guidance for The leaf rises because it is repelled by the stem support. The leaf and its support have the same type of charge. A typical school electroscope will show a deflection for a charge as small as 0. Charging by contact. Rub an insulator to charge it up. Then stroke it across the top plate of the electroscope. This will transfer charge from the insulator to the electroscope. This method is direct and clear to students.
However, the charge left on the electroscope will not always leave it fully deflected. Charging by induction. This is a quick way to get a larger charge onto the electroscope. However, it can look a bit magical to students. So it should be used with some care. This will induce the opposite charge on the plate of electroscope leaving a net charge on the gold leaf, which will rise.
Now touch the plate with you finger momentarily to earth it still holding the charged insulator near the top plate. The charge on the top plate will be neutralised but there will still be a charge on the gold leaf. Let go of the plate and then take the charged insulator away.
The charge that had been pushed down to the gold leaf will now redistribute itself over the plate and the leaf, leaving the whole thing charged. The leaf will show a good deflection. You can use a flying lead connected to one of these high voltage sources to charge up the gold leaf electroscope.
This is quick, effective and obvious to students. The other terminal of the supply should be earthed. Connect the flying lead to the supply through a safety resistor. The electroscope can be used to demonstrate that a small current is flowing in a circuit — for example in experiments to show the ionisation of the air.
Using the hook rather than the plate makes the electroscope more sensitive to small amounts of charge. A charge of around 0. So it is possible to watch it rise or fall slowly due to a current as small as 1 pA. Put the electroscope in series as though it were an ammeter.
Any charge that flows in the circuit will move onto the electroscope making the gold leaf rise. You may need to discharge the electroscope when you first switch on the power supply because there will be an initial movement of charge due to the capacitance in the circuit.
Alternatively, you can use the electroscope as a source of charge and watch it discharge. It is like a capacitor with its own display. Charge it up and then connect it into a circuit. If the circuit conducts, the electroscope capacitor will discharge and, at the same time, the leaf will display how much charge is left. The electroscope has a very high as good as infinite resistance.
If you earth the electroscope case, the electroscope measures potential so it is well suited to detecting potentials in electrostatic experiments. Without earthing, the quantity it is measuring is charge. This is related to p. Capacitance depends on the position of the electroscope, people nearby and so on. School electroscopes are open to the air more refined ones are in a vacuum. Cosmic radiation will ionise this air and cause a small leakage current. So the electroscope will discharge over time.
Historically, the discharging of electroscopes led to the suggestion of the existence of cosmic radiation. Victor Hess and Carl Anderson shared the Nobel Prize for Physics in , for discoveries related to cosmic radiation. The Nobel Award ceremony speech describes their work:.
Nobel Prize in Physics Award ceremony speech. For 6 Resources. Cloud chambers provide a satisfying and captivating activity for students, allowing For 17 Resources.
A unit used to provide an everyday measure of radiation dose. A single banana produces an ionising radiation dose of around Stories from Physics Demonstration: this demonstration focuses on the properties of gamma radiation. You can show that it is much more penetrating Practical Activity Now that your students are familiar with different types of radiation, you can look at the processes by which they are emitted Lesson Want to ask it in a safe, friendly, knowledgeable environment?
TalkPhysics is an online community for anyone involved in the teaching of pre physics. Ionising Radiation. Appears in these Collections Curated Collection Ionising the air The air can be ionised by flames, radioactive sources and strong electric fields Curated Collection Cloud chambers Cloud chambers provide a satisfying and captivating activity for students, allowing Ionising Radiation Quantum and Nuclear.
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The gold leaf electroscope
Teaching Guidance for The leaf rises because it is repelled by the stem support. The leaf and its support have the same type of charge. A typical school electroscope will show a deflection for a charge as small as 0. Charging by contact. Rub an insulator to charge it up. Then stroke it across the top plate of the electroscope.
Gold Leaf Electroscope – 1787
Practical Activity for The device is used for detecting electric charge and can also identify its polarity, if compared with a known charge. For 10 Resources. Martinus van Marum's machine: Martinus van Marum, a Dutch physician, developed an interest in the physical sciences and was Stories from Physics Demonstration: a shuttling ping-pong ball serves as a model of ions moving in an electric field. Practical Activity
1.4: Experiments with a Gold-leaf Electroscope
For centuries, the electroscope was one of the most popular instruments used by scientists to study electricity. Abraham Bennet first described this version in An electroscope is a device used to detect an electric charge. For centuries, it was one of the most popular instruments used by scientists to study electricity. His device, dubbed the versorium , consisted of a lightweight needle balanced on a pivot. The presence of electricity in a nearby object caused the needle to move.