Temat 14: What is electricity?

The answer to this question is: Electricity is more the name for a field of inquiry, and less the name for any specific observation or effect. Electricity is not a specific term; the term is used to refer to the effects of electric charges, of their motion and their fields. In fact the vocabulary issue hides a deeper question: what is the nature of electric charge? In order to solve this issue, we start with the following question.

Can we detect the inertia of electricity?
If electric charge really is something flowing throughmetals, we should be able to observe the effects shown in Figure 12: electric charge should fall, should have inertia and should be separable from matter. And indeed, each of these effects has been observed.

FIGURE 12 Consequences of the flow of electricity.

For example, when a long metal rod is kept vertically, we can measure an electrical potential difference, a voltage, between the top and the bottom. In other words, we can measure the weight of electricity in this way. Similarly, we can measure the potential difference between the ends of an accelerated rod. Alternatively, we can measure the potential difference between the centre and the rim of a rotating metal disc.The last experiment was, in fact, the way in which the ratio q/m for currents in metals was first measured with precision.
The result is:
q/m ≈ −1.8(2) ⋅ 10¹¹ C/kg (7)
for all metals, with small variations in the second digit. The minus sign is due to the definition of charge. In short, electrical charge in metals has mass, though a very small one.
If electric charge hasmass, whenever we switch on an electrical current, we get a recoil. This simple effect can easily be measured and confirms themass to charge ratio just given. Also, the emission of current into air or into vacuum is observed; in fact, every cathode picture. The emission works best for metal objects with sharp, pointed tips. The rays created this way – we could say that they are ‘free’ electricity – are called cathode rays. Within a few per cent, they show the same mass to charge ratio as expression (7). This correspondence thus shows that charges move almost as freely in metals as in air; this is the reason that metals are such good conductors of electric current.
If electric charge falls inside vertical metal rods, we can make the astonishing deduction that cathode rays should not be able to fall through a vertical metal tube. As we will see later, cathode rays consist of free electrons. The name ‘electron’ is due to George Stoney. Electrons are the smallest and lightest charges moving in metals; they are, usually – but not always – the ‘atoms’ of electricity. In particular, electrons conduct electric current inmetals. The charge of an electron is small, 0.16 aC, so that flows of charge typical of everyday life consist of huge numbers of electrons; as a result, electrical charge effectively behaves like a continuous fluid. The particle itself was discovered and presented in 1897 by Johann Emil Wiechert (b. 1861 Tilsit, d. 1928 Göttingen) and, independently, three months later, by Joseph John Thomson (b. 1856 Cheetham Hill, d. 1940 Cambridge).
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The speed of electricity is too slow for many people. Computer chips could be faster if it were higher. And computers that are connected to stock exchanges are located as near as possible to the stock exchange, because the time advantage the short communication distance (including the delay inside switching chips) provides is essential for getting a good financial performance in certain trading markets.
In summary, experiments show that all charges have mass. And like all massive bodies, charges move slower than light. Charge is a property of matter; images and light have no charge.