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Published byPenelope Meryl Stokes Modified over 3 years ago

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

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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…

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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

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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

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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

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

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Symbols Complete the electric circuit symbols worksheet

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Symbols

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Symbols

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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

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Circuit 1 Circuit 1 – basic series circuit +-

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

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

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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…

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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

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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

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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

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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

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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)

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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)

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