The electric field became the mechanism for explaining the Coulomb force. In the case of Coulomb forces, however, the objections were overcome when the British experiment physicist Michael Faraday proposed the electric field as an alternative to the concept of force acting through empty space. How, they asked, was the force exerted through empty space? The tremendous success of the law of gravity in explaining terrestrial and celestial motion dispelled all objections to gravitation. Joseph Priest, in International Edition University Physics, 1984 PreviewĬoulomb's law of electric force, like Newton's law of universal gravitation, left many scientists uneasy. In both cases, positive and negative, the interior of the sphere remains uncharged. Alternatively, when such a sphere is charged positively, the material of the interior retains its free electrons, while the surface layers have a deficiency and so display a positive charge. When a solid conducting sphere is charged negatively, the excess electrons distribute themselves around the surface only. The chapter also discusses numerical problems on spheres. Moreover, the potential difference, in volts, between two points in an electric field is defined as the work per unit charge, in joules per coulomb, required to move a positive charge from one point to the other. Thus, at the position of Q 2, the electric field strength E 1 because of Q 1 is F/Q 2 in newton per coulomb. Each charge is said to produce an electric field, the strength of which, at any point, is measured by the force exerted per unit charge at that point. (HONS.), A.INST.P., in Calculations in Fundamental Physics: Electricity and Magnetism, 1971 Publisher SummaryĬoulomb's law states that the force F between two point charges, Q 1 and Q 2, in a vacuum is proportional to their product and inversely proportional to the square of their distance apart r. The relative change in number of electrons in tiny, and so the chemical nature of the copper remains unchanged. There are 220 million electrons in our 5 gm of copper for every one electron we add. The 1 mC we add amounts to 6.24 x 10 15 electrons. But what of the effect of the charge on the chemical nature * of the copper? Our 5 gm of copper contains about 1.37 x 10 24 electrons (and an equal number of protons). Because of the great strength of the electrical force, this 1-mC charge can exert a very significant force. Suppose that we have 5 gm of copper (equal in mass to a nickel), and that we place 1 millicoulomb (mC) of negative charge (electrons) on this copper. There is a second and more immediate consequence of the strength of the electrical force. (Gravity dominates when the masses are large-like planetary or stellar masses-and the net electric charges are small.) A consequence of the strength of the electrical force is that the universe must be almost exactly neutral. Imagine grains of sand so fine that you can pack 10 6 grains in 1 cm 3: 10 39 of these grains would occupy the volume of a million earths! Clearly the Coulomb electrical force is far stronger than gravity, at least for electrons and protons. The number 10 39 is a tremendously large number.
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