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What is Electricity? Electricity is the flow of moving electrons. When the electrons flow it is called an electrical current. Cells and batteries Cells and batteries Electric Current Electric current is the rate at which charges pass a given point. When the current is high, more charges pass the point each second. Electric Current • Symbol of current in formula: I • Units: amperes or amps • Symbol of amperes or amps: A AC/DC There are two types of electric current: Alternating Current (AC) and Direct Current (DC) Voltage Voltage is the potential difference between two points in a circuit. Voltage is the potential energy that makes the electrical current flow in a circuit by pushing the electrons around. Voltage • Symbol of voltage in formula: V • Units: volts • Symbol of volts: V Voltage • A measure of how much work is needed to move a charge between two points. • The size of the current depends on the voltage. If the voltage between two points on a wire is increased, more current will flow in the wire. What is a resistance? Resistance is the opposition to the flow of electric charge. Resistance • Symbol of resistance in formula: R • Units: ohms • Symbol of ohms: Ω Conductors and insulators • A conductor in electricity is a material that allows electrons to flow through it easily. Metals, in general, are good conductors. • An insulator is a material that is a poor conductor of electricity. Examples include plastic, wood, ceramic and glass. Conductance • Symbol of conductance in formula: G • Units: Siemens • Symbol of ohms: S • To calculate conductance in terms of Resistance, we use this formula: R= 1/G G= 1/R V I V=IxR R I=V/R R=V/I Exercises 1. What current flows between a potential difference of 120 V through a resistance of 30 Ω? 2. A motor with an operating resistance of 30 Ω is connected to a voltage source. 4.0 A of current flow in the circuit. What is the voltage of the source? 3. If the conductance of a circuit is 0.25 S, and the current is 2.0 A, what is the overall voltage? 4. An ammeter measures current. What will the ammeter read when it is connected to a 90 V source and a 60 Ω resistor? Electrical Power • The rate at which electrical energy is changed into other forms of energy. The watt tells how quickly a device (e.g. bulb) uses electrical energy. • Symbol of power in formula: P • Units: watts (Joules/s) • Symbol of watts: W Power= voltage x current
