Current Electricity

• The definition of current is the rate of flow of charge per unit time. I is ampere(A). Q is charge(c). t is time(s) $I=$$Q/t$
• Conventional current is the current that flows in a circuit when there is a potential difference across it.
• Convectional Current flows from positive terminal to negative terminal.
• Electron flow travels opposite direction to conventional current.
• Short circuit is when current flow in path of 0 resistance.
• There are several components such as cell, battery, switch, fixed resistor, variable resistor(thermostat), thermistor, light dependent resistor, fuse, diode, light emitting diode(L.E.D.), bulb, transformer, motor, ammeter, voltmeter, and galvano meter.
• Electromotive force(e.m.f.) refers to the work done to push 1C of charge round a complete circuit.
• Units of e.m.f. is volts(V).
• A voltmeter have infinite resistance, needing it to always be connected in parallel.
• Potential Difference also known as p.d. is the work done to push 1C of charge through a component. Such components like bulb, resistors, motors.
• Units of p.d. is volt(V)
• Both e.m.f and p.d. formula is $Pd=$$W/Q$ and $EMF=$$W/Q$ where W is work done(J) and Q is charge (C)
• Resistance controls current and is indirectly proportional to current. When resistance increase, current will decrease.
• Definition of resistance is ratio of the potential difference across a component to the current flowing through it.
• Ohm’s Law can be broken into three parts. First is metallic conductor. Secondly, $V<I$ . Thirdly, physical conditions remain constant.
• Definition of Ohm’s Law is for a metallic conductor, the potential difference across a component is directly proportional to the current flowing through it, provided the physical conditions remain constant.
• For a component to be an ohmic device, gradient of V-I graph

  =R have to be constant.
• Non-Ohmic device in V/v / I/A graph, if increasing, resistance is increasing therefore increasing resistance. If gradient is decreasing, resistance is decreasing. For a graph to show a component is a ohmic device, the graph have to start from 0.
• I/A / V/v graph if gradient is increasing, 1/R is increasing and therefore, resistance is decreasing. If gradient is decreasing, 1/R is decreasing and therefore, resistance is increasing.
• Non Ohmic devices includes filament lamp and diode. The reason for filament lamp is when current increases, temperature increases resulting in increasing resistance. The reason for diode is because it allows current to flow in one direction only.
• The factors affecting resistance in wires is 1. Length 2. Cross-sectional area 3. Resistivity. When length of wire increases, resistance increases. When cross-sectional area increases, resistance decreases. Resistivity is material dependent. When density increases, resistance increases. $R=$$PL/A$ where R is in ohm, P(rho) is in ohm meter, L is in meter and A is in meter squared.