To show that equal and opposite charges are produced by friction Whenever an ebonite rod is rubbed with fur the fur becomes charged as well as the ebonite, but with electricity of opposite sign. The same remarks apply to the case of glass rubbed with silk, or indeed to any pair of substances. Moreover, the two opposite […]
Faraday’s ice-pail experiments A particularly successful application of the properties of electric field lines has been made in the explanation of Faraday’s ice-pail experiments on electrostatic induction. These experiments have nothing to do with ice, but owe their name simply to the fact that Faraday used an empty ice pail as a convenient hollow conductor. In the first […]
Electric fields An electric charge sets up an electric field in the space surrounding it and an electric force is exerted on any charged body placed in the field. Electric fields may be represented by eLectric field lines. An electric field line is a line drawn in an electric field such that its direction at any point gives the […]
The lightning conductor Based on the experiments described above, Franklin considered that it ought to be possible to protect a building from lightning damage by fixing, to the side of the building, a long pointed iron rod with its lower end buried in the earth. Tests were soon to prove the method successful. In present-day practice a lightning […]
Atmospheric electricity. Franklin’s experiments About the middle of the eighteenth century the American scientist, Benjamin Franklin, came to the conclusion that lightning was a gigantic electric spark discharge occurring between two charged clouds or between a cloud and the earth. He had previously shown that it was possible to draw electricity from clouds by sending up a kite during […]
Points as collectors of charge A sharp point not only enables a conductor to lose charge but it can also act as a collector of charge. This aspect of point action can be shown by the following experiment. A gold-leaf electroscope is provided with a sharp point by placing a needle or a piece of wire on the […]
To demonstrate the presence of both positive and negative ions in a flame Before proceeding further with our discussion of point action we must draw the reader’s attention to an effect which is observed when the wire from a conductor of an electric machine is placed very close to a candle flame (Fig. 32.18). On starting up the machine […]
Action of highly charged points When a sharp pointed wire is connected to the conducting knob of a Wimshurst or other electric machine, and the machine set in motion, the surface density of charge on the point becomes exceedingly high and a current of air known as an electric wind streams away from the point. This electric wind […]
Electric machines When a considerable quantity of static electricity is required an electric machine is used. The earliest machines which were constructed in the seventeenth and eighteenth centuries worked by friction. For example, Otto von Guericke used a rotating sulphur-ball to which a dry hand was applied to produce the friction. Later experimenters used glass spheres or discs […]
Ions in the atmosphere Ionization by the process described above is only one way of producing gaseous ions. Another method is to allow high-energy radiation to pass into the gas. Various experiments have shown that the atmosphere contains ions which have been produced by radiation from radioactive minerals in the earth’s crust, by ultraviolet light from the sun and […]