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Currents CIRCUITS S.MORRIS 2006 More free powerpoints at www.worldofteaching.com 2 types of electric currents AC = Alternating current • Electrons in the circuit move in 1 direction for some time and then switch directions and go the opposite way • Ex: household outlets and appliances •DC = Direct current • Charges always flow in the same direction • From negative to positive • Ex: batteries The CELL – the power source Cells are a type of voltage source that converts chemical energy into electrical energy when a circuit is connected. When two or more cells are connected together we call this a Battery. What is an electric circuit? Any pathway through which electrons can flow/travel + - The bare essentials for a circuit: • battery/power source • Load (lightbulb/lamp) • Wires One more piece… Most circuits also have a switch that is used to turn the circuit on and off when the switch is open, it creates a gap so that electrons cannot flow when the switch is closed, the circuit is complete and electrons can move through it types of circuit There are two types of electrical circuits; SERIES CIRCUITS PARALLEL CIRCUITS SERIES CIRCUITS The components are connected end-to-end, one after the other. They make a simple loop for the current to flow round. A break anywhere in the loop will result in an open circuit and no more moving electrons If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out. PARALLEL CIRCUITS The components are connected side by side. The current has a choice of routes. If there is a break in one path, it might not effect the other path circuit diagram Scientists usually draw electric circuits using symbols; cell lamp switch wires measuring current Electric current is measured in amps (A) using an ammeter which is connected in series in the circuit. A measuring current This is how we draw an ammeter in a circuit. A A SERIES CIRCUIT PARALLEL CIRCUIT measuring current SERIES CIRCUIT • current is the same at all points in the circuit. 2A 2A 2A PARALLEL CIRCUIT • current is shared between the components 2A 2A 1A 1A Discuss with your neighbor what the missing ammeter readings would be 3A ? 4A ? 3A 1A ? 4A ? 4A 1A 1A ? measuring voltage The ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter which is drawn across (on top of) circuit components V measuring voltage This is how we draw a voltmeter in a circuit. V V V SERIES CIRCUIT V CIRCUIT PARALLEL series circuit • voltage is shared between the components 3V 1.5V 1.5V parallel circuit • voltage is the same in all parts of the circuit. 3V 3V 3V Let’s recap: Series Circuit Current Voltage Parallel Circuit measuring current & voltage copy the following circuits on the next two slides. complete the missing current and voltage readings. remember the rules for current and voltage in series and parallel circuits. measuring current & voltage a) 6V 4A A V V A measuring current & voltage b) 4A 6V A V A V A answers a) b) 4A 6V 6V 4A 6V 4A 4A 3V 2A 3V 4A 6V 2A measuring resistance in series In series: to find total resistance of a series circuit, add the individual resistances of the objects in series 6V 3Ω 2Ω The total resistance of this circuit would be 5 Ω What happens to voltage as you move past each light? -It drops – we can calculate the “voltage drop” of each light using Ohm’s law 6V 3Ω 2Ω measuring resistance in parallel In parallel, use the following formula to find the total resistance: 6V 6V 3Ω RT = R1 x R2 = R1 + R 2 2Ω Total resistance in parallel will always be less than the smallest resistor