Electricity

• Current is the flow of charge, measured in ampères, or amps (A).
• The Vrms = 6.4 X √2 = 4.5 V.
• Charge is measured in coulombs (C), which is defined as: 1 coulomb is the quantity of charge carried past a given point if a steady current of 1 amp flows for 1 second.
• 1 electron carries a charge of 1.6 ´ 10-19 C.
• 1 coulomb is equivalent to 6.2 ´1018 electrons.
• Charge and current are linked by a simple formula: Charge (C) = current (A) X time (s).
• There are some important multipliers for current: 1 microamp (1µA) = 1 X 10 -6 A, 1 milliamp (mA) = 1 X 10 -3 A.
• Chemical reactions inside a cell help to create a small POTENTIAL DIFFERENCE between the terminals and this makes the electrons flow along any conducting path that connects them.
• A current (flow of charge) will flow through an electrical component (or device) only if there is a voltage or potential difference (p.d.) across its ends.
• The bigger the potential difference across a component, the bigger the current that flows through it.
• The conducting path through the bulbs, wire and battery is called a circuit.
• Ohm’s Law states that the current in a metallic conductor is directly proportional to the potential difference between its ends provided that the temperature and other physical conditions are the same.
• An ohmic conductor is a conductor that obeys Ohm’s Law.
• Voltage and current can be measured and plotted as a graph called a VI characteristic.
• The gradient of a voltage current graph determines the resistance.
• A filament lamp’s resistance rises as the filament gets hotter, which is shown by the gradient getting steeper.
• A thermistor’s resistance goes down as it gets hotter because the material releases more electrons to be able to conduct.
• The diode characteristic graph looks like this: The diode starts to conduct at a voltage of about +0.6 V, which is called forward bias, and then the current rises rapidly for a small rise in voltage.
• If the current is reversed (reverse bias), almost no current flows until the breakdown voltage is reached, which usually results in destruction of the diode.
• Resistivity is a property of the material and is defined as the resistance of a wire of the material of unit area and unit length.
• In a series circuit, the electrons in the current have to pass through all the components, which are arranged in a line.
• In a parallel circuit, the current splits into the number of branches there are.
• The cell is a source of Chemical potential energy.
• The cell does work on electrons and the electrons gain Electrical potential energy (we call it just potential energy).
• P.D

  (Potential difference or Voltage) across battery terminals indicates the potential energy given to each coulomb (approximately 1018 electrons) of charge.
• If 1 Joule of energy is given to 1 Coulomb of electric charge by the battery then we say that the p.d

  across the cell is 1 Volt.
• When the charges move through the wire they do not lose any of the potential energy they are carrying.
• When they pass through something that resists their flow, they will have to do work.
• If two or more resistors are connected in parallel, they give a lower resistance than any one of the resistors by itself.
• Kirchhoff's Laws: The algebraic sum of currents at a junction is zero, and around a closed circuit loop, the algebraic sum of the e.m.f.s is equal to the algebraic sum of the p.d.s.
• Kirchhoff I: The algebraic sum of currents at a junction is zero.
• Kirchhoff II: Around a closed circuit loop, the algebraic sum of the e.m.f.s is equal to the algebraic sum of the p.d.s.
• Batteries convert chemical energy into electrical energy, and generators turn kinetic energy into electrical energy.
• A battery does a job of work in pumping the electrons around the circuit.
• Positive charges do not move.
• A battery is said to produce Emf (electromotive force) which is defined as the energy converted into electrical energy when unit charge passes through the source.
• The energy supplied to a circuit by a battery is given by: W = Q * ε, where W is the energy in J, Q is the charge in C, and ε, curly E is the physics symbol for emf.
• No circuit at all is 100 % efficient, some energy is dissipated in the wires, or even in the battery itself.
• All batteries and generators dissipate heat internally when giving out a current, due to internal resistance.
• A perfect battery has no internal resistance, but unfortunately there is no such thing as a perfect battery.