Electromotive concept - Solutions - Huaqiang Electronic Network

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Regarding the concept of electromotive force, the following points should be clarified:
(1) The electromotive force is a physical quantity indicating the power of the power source to convert other forms of energy into electric energy. A power source is a device that converts other forms of energy into electrical energy. Each power supply has a positive and a negative pole at any one time. There is some kind of non-electric field force inside the power supply, which can overcome the electric field force and work, forcing the positive electric charge to move from the negative pole of the low potential point to the positive pole of the high potential point through the internal power source, and convert other forms of energy into electric energy in the process. . In order to characterize the ability of the non-electrical force inside the power supply to work on positive charges, or to express the ability of other forms of energy to be converted into electrical energy, the concept of electromotive force is introduced.
(2) The electromotive force of the power source is equal to the work done by the internal non-electric field force to move the unit positive charge from the negative electrode to the positive electrode. The unit is the same as the voltage. The magnitude of the electromotive force depends on the power supply itself and is independent of the external circuit. Any electromotive force is indicated by e. For a DC electromotive force whose magnitude and direction do not change with time, it is generally expressed by E, and can also be represented by e.
(3) It is customary to specify the true direction of the electromotive force, which is the low potential point and the negative pole points to the positive pole of the high potential point, that is, the direction in which the potential rises. This is exactly the opposite of the true direction of the voltage.
(4) Electromotive force and voltage are two different concepts. The former is the work done by the non-electric field force moving the positive charge from the vicinity of the low potential point to the positive point of the high potential point; and the latter is the work done by the electric field force moving the unit positive charge from the high potential point to the low potential point. However, they can all be used to indicate the potential difference between the positive and negative terminals of the power supply. In the closed circuit, the objective effect of the performance of the external circuit from the power supply, as shown in Figure 1-3, can be expressed by the electromotive force e between the positive and negative electrodes ab, or by the voltage U between them. . It should be noted that the reference directions of the two are just the opposite.