If a voltage is applied across a capacitor by connecting the capacitor to a bat- tery with conducting wires as in Fig. 17–14, charge flows from the battery to each of the two plates: one plate acquires a negative charge, the other an equal amount of positive charge. Each battery terminal and the plate of the capacitor connected to it are at the same potential; hence the full battery voltage appears across the capacitor. For a given capacitor, it is found that the amount of charge Q acquired by each plate is proportional to the magnitude of the potential difference V between the plates: Q = CV. (17–7) The constant of proportionality, C, in Eq. 17–7 is called the capacitance of the capacitor. The unit of capacitance is coulombs per volt, and this unit is called a farad (F). Common capacitors have capacitance in the range of 1 pF (picofarad = 10 12F) to 10° µF (microfarad = 10 F). The relation, Eq. 17-7, was first suggested by Volta in the late eighteenth century. In Eq. 17–7 and from now on, we will use simply V (in italics) to represent a potential difference, such as that produced by a battery, rather than Vpa, AV, or V - Va, as previously.
Dielectric Constant Of Water
Water constitutes about 70% of earth. Some important distinguishing properties of water are high molar concentration, small dissociation constant and high dielectric constant.
Electrostatic Potential and Capacitance
An electrostatic force is a force caused by stationary electric charges /fields. The electrostatic force is caused by the transfer of electrons in conducting materials. Coulomb’s law determines the amount of force between two stationary, charged particles. The electric force is the force which acts between two stationary charges. It is also called Coulomb force.
We have seen that the capacitance C depends on the size
and position of the two conductors, as well as on the
dielectric constant K. What then did we mean when we
said that C is a constant in Eq. 17–7?


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