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Rev. Notes > IGCSE > Elecrical Quantities
Previous Topic Elecrical Quantities Next Topic

Electric charge One Coulomb Charge Production of electric charge
Detection of electric charge Experiment to detect the electric charge Electrical conductors and insulators
Electric field Electrostatic forces Application of electrostatic forces
Electric current One Ampere of electric current Direction of electric current
Basic relation of electric current Direct current Alternating current
Ammeter Electromotive force - (e.m.f.) Potential difference
One Volt Explanation of potential difference Measurement of potential difference
Voltmeter Resistance Affect of length of the conductor on resistance
Affect of cross-sectional area on resistance Affect of temeprature on resistance How nature of material affects the eresistance
Ohm's law Potential difference - Current graph for Ohmic conductors Potential difference - Current graph for tungsten filament
Potential difference - Current graph for semiconductor diode Electrical energy Formula for electrical energy
Electrical Power Formulae for electrical power

Experiment to detect the electric charge

(1) To detect the presence of charge on a body: If a rod of some suitable material is charged by friction and then brought near to the cap of gold-leaf electroscope, the leaf is seen to diverge from the plate. A charge has been induced on the leaf and plate, and consequently repulsion occurs between them. On removing the charged rod, th eleaf collapses, showing that the induced charge on the electroscope is only temporary. (Very small charges may be detected by this method)

(2) To charge a gold-leaf electroscope by contact: Generally speaking,it is not always easy to charge an electroscope by contact with a charged rod but usually it can be done after a few attempts. An ebonite rod is given a small charge by rubbing with fur, and is then rolled over the cap of an electoscope. The leaf will be seen to diverge, and then the rod is removed. If the leaf does not stay diverged the process is repeated untill it does. we may now assume that the electroscope is charged with negative electricity by conduction from the ebonite rod.

If the cap of the elecrtoscope is touched with the fingure, the charge flows to earth through the experimenter's body, and the leaf collapses. This is called "eathing the electroscope". Before proceeding any further it must be pointed out that harging by contact is not a good methos and often gives a charge opposite to that epected. it is better to use the method of induction.

(3) To test for the sign of the charge on a body: Having charged the electroscope negatively as described above, the ebonite rod should be rechared and brought near to the cap. An increase in the leaf divergenece is noted.

A glass rod rubbed with silk (positive charge) is now coutiously brought own towards the cap from a hight of about 50 cm. This time, a decrease in divergence is noticed.

The electroscope is discharged by touching it with the fingure and afterwards charged positively by contact, using a glass rod rubbed with silk. We shall now find that an increase divergence is caused by bringing a charged glass rod near the cap and a decreased divergence by charged igonite rod.

Conclussion of the above experiments: An icrease in divergence occurs when the charge on the electroscope and the test charge are of the same kind.

(4) To test the insulating properties of various materials: The insulating or, conversely, the conducting property of a given substance may be tested by holding a sample of the substance in the hand and then bringing it in to contact with the cap of a charged electroacope. If the substance is a good insulator, there will be no leakage of a charge through it anf the leaf divergence will not alter. If, however the leaf colapses instantly it shows that the substance is a good conductor.

Between these two extremes there are certain subatances, which produce a slow collaps of the leaf. Thease are classed as poor insulators or poor conductors. Examples of this type of material are paper, wool, cotton and wood. Nevertheless, if these substances are dried throughly, they become quite good insulators. This suggests that there ability to conduct electricity comes from there moisture contents. Among the good conductors are all the metal and carbon. The good insulators are sulphure, quartz, paraffin wax, polyvinyl chloride (P.V.C.) shellac, polythene and silk.





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View Comments on this Chapter - Total Comments (6)
sree Said :
wish these had a diagrams
  24/12/15 10:01 AM
student 567 Said :
There are no diagrams, but seeing that you don't give a shit... why should i bother to comment?! Can you just put the dam diagram up already!
  18/04/14 08:10 PM
Deepak varun Said :
there is a spelling mistake to say said they said asaid please change it admin
  17/11/13 06:26 AM
gargi sachdev Said :
diagrams aren't there ...
  29/08/12 12:35 AM
gargi sachdev Said :
diagrams aren't there ...
  29/08/12 12:35 AM
Ajay Said :
I cant see any diagrams? can u help me with it
------------------------------------------------------------------------------------- Admin Replied:

Hi Ajay, thank you for informing us about this issue. We will make sure we make those images available for you as soon as possible.

Thank you

  15/03/12 12:13 PM


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