Capacitors and batteries Firdiana Sanjaya( ) Ana Alina( )

Definition of Capacitance  The capacitance C of a capacitor is defined as the ratio of the magnitude of the charge on either conductor to the magnitude of the potential difference between the conductors:  Capacitance has SI units of coulombs per volt. The SI unit of capacitance is the farad (F), which was named in honor of Michael Faraday

Capacitors: devices for storing charge

Parallel-Plate Capacitors  The charge stored in a capacitor is proportional to the potential difference between the two plates. For a capacitor with charge Q on the positive plate and -Q on the negative plate, the charge is proportional to the potential:  Q = C V

Parallel-Plate Capacitors

The Spherical Capacitor

Capacitors with Dielectrics  A dielectric is a nonconducting material, such as rubber, glass, or waxed paper. When a dielectric is inserted between the plates of a capacitor, the capacitance increases. If the dielectric completely fills the space between the plates, the capacitance increases by a dimensionless factor k, which is called the dielectric constant of the material.

Combinations of Capacitors Series Combination

Combinations of Capacitors Parallel Combination

Energy stored in a capacitor  When a capacitor is being charge,positive charge is transferred from the negatively charged conductor to the positively charged condustor.Work must therefore be done to charge a capacitor.

Energy stored in a capacitor

Batteries and EMF  Batteries are capacitors that very good at storing charge for short time periods, and they can be charged and recharged very quickly.  A battery consists of two electrodes, the anode (negative) and cathode (positive. Usually these are two dissimilar metals such as copper and zinc. These are immersed in a solution (sometimes an acid solution). A chemical reaction results in a potential difference between the two terminals.

 The voltage of a battery is also known as the emf, the electromotive force.  Emf can be thought of as the pressure that causes charges to flow through a circuit the battery is part of.  A flow of charge is known as a current.  Batteries put out direct current.

Current and Drift velocity  Current (I) is measured in amperes (A), and is the amount of charge flowing per second. I = q / t  The flow of positive charge in one direction is equivalent to the flow of negative charge in the opposite direction.  The direction of the drift velocity is opposite to the electric field.  In a typical case, the drift velocity of electrons is about 1 mm / s. The electric field, on the other hand, propagates much faster than this, more like 10 8 m / s.

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