Electric Circuits  To calculate the size of a current from the charge flow and time taken Thursday, August 06, 2015

Electricity  Energy can never be created or destroyed, it can only ever be converted from one form to another  Energy is only useful when it is converted from one form to another  Electricity is so useful because it can be easily transferred…

Electricity  Electricity is the flow of electrical power (charge) in the form of electrons  Electricity is a useful secondary energy source – most energy sources (like coal, oil, nuclear, wind etc…) can be converted into electricity

Circuits  A bulb in the circuit is like a radiator – an electrical device uses electrical energy, supplied by the circuit  The wires are like pipes - they carry the flow of electricity (current) around the circuit  The electrical current is pushed by the cell (battery) – this is the voltage  The electrons flow from –ve to +ve +- Cell Wires Lamp

Electrical Circuits  An electric current needs two things: -  Something to make the electricity flow (battery or power pack)  A complete circuit  Without these two basic things, an electric current will not flow +- Cell Wires forming a complete circuit

Component Diagrams  Circuit symbols are used to show the components in an electrical circuit (wires are represented by straight lines)

Symbols  Complete the electric circuit symbols worksheet

Symbols

Symbols

Task  Your task is to set up some simple circuits using the minimum number of components necessary – you will have 3 minutes to set up each circuit… +- Cell Wires Lamp Switch

Circuit 1  Circuit 1 – basic series circuit +-

Circuit 2  Circuit 2 – basic series circuit with ammeter (move this around to and note the current at different points) and voltmeter +- V A

Circuit 3  Circuit 3 – basic parallel circuit with ammeter and voltmeter V V +- A

Circuit Experimentation  Finally, experiment with the circuits (both series and parallel) – use the ammeters and voltmeters at different points within the circuits to try and establish some rules for the current and voltage…

Series Circuits  Components that are connected one after another on the same loop of the circuit are connected in series  If you remove or disconnect one component, the circuit is broken and they all stop +- V A A 5Ω5Ω 4Ω4Ω 3Ω3Ω VV 6V 2.5V 2V1.5V  Voltages add to equal the supply 1.5V + 2V + 2.5V = 6V  Total resistance 3 Ω + 4 Ω + 5 Ω = 12 Ω  Current = voltage ÷ resistance 6 ÷ 12 = 0.5A

Series Circuits  The same current flows through all parts of the circuit  The total resistance is the sum of all the resistances  The size of the current is determined by the total p.d of the cells and the total resistance of the circuit (I = V/R)  The total p.d of the supply is shared between the various components, so the voltages around a series circuit always add up to equal the total voltage of the supply  The bigger the resistance of a component, the bigger its share of the total p.d

Parallel Circuits  Each component is separately connected to the +ve and –ve of the supply  Removing or disconnecting one component hardly affects the others at all  Voltages all equal the supply voltage (6V)  Total resistance the is less than the smallest (i.e. less than 2 Ω )  Total current = the sum of all the branches 1.5A + 3A + 1A = 5.5A +- V A1A1 4Ω4Ω 6V A2A2 1.5A V 2Ω2Ω 6V A3A3 3A V 6Ω6Ω 6V A4A4 1A

Parallel Circuits  All components get the full source p.d, so the voltage is the same across all the components  The current through each component depends on its resistance – the lower the resistance, the greater the current which flows through it  The total current flowing around the circuit is equal to the total of all the currents in the separate branches (the total current going into a branch always equals the total current leaving the branch (no current is lost))  The total resistance of the circuit is always less than the branch with the smallest resistance

Current Current = Charge ÷ Time I = Q ÷ t  Current is measured in amperes (A)  Charge is measured in coulombs (C)  Time is measured in seconds (s)

Potential DifferencePotential Difference P.D. = Work done ÷ Charge V = W ÷ Q  Potential difference is measured in volts (V)  Work done is measured in joules (J)  Charge is measured in coulombs (C)