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Electricity

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Electrical conductors and insulators

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Electric Current When electric charges move in a wire, we say that an electric current flows in the wire. It's like the way a current of water flows in a river. For an electric current to flow, we need two things: something to make the electricity flow, such as a battery or power packsomething to make the electricity flow, such as a battery or power pack a complete path for the current to flow in. This is called an electric circuit.a complete path for the current to flow in. This is called an electric circuit.

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An electric circuit is a path along which current flows. current flows. Current can only flow through a closed circuit. Battery provides energy in a closed circuit and current transports energy from the and current transports energy from the battery to the bulb. battery to the bulb.

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Do all materials allow electricity to flow through them? What kind of materials allow electricity to flow through them?

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Identify electrical conductors and electrical insulators.

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Infer that good conductors of electricity are generally good conductors of heat.

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Heat conductors are materials that allow heat to pass through it easily. Examples: Metals - silver, iron, copper, aluminum. Silver Copper

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Electrical conductors are materials that allow electric current to flow through.

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What types of materials are good electrical conductors? Alumiuium?Rubber?Wood?

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Electrical insulators are materials that do not allow electric current to flow through.

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What types of materials are electrical insulators? Glass? Pencil lead?

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Electric Circuits

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Electric circuits

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Circuit Symbols

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circuit diagram cellswitchlampwires Scientists usually draw electric circuits using symbols;

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Would This Work?

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The Central Concept: Closed Circuit

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Circuits Series Parallel Circuits Series Parallel

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Predict, Test and Explain How will the brightness of the bulbs change as we add more in series?How will the brightness of the bulbs change as we add more in series? What does this imply about the current in the circuit?What does this imply about the current in the circuit? + + +

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Predict, Test and Explain How will the brightness of the bulbs change as we add more in parallel?How will the brightness of the bulbs change as we add more in parallel? What does this imply about the current in the circuit?What does this imply about the current in the circuit? + ++

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Short circuit

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What would happen?

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Why are the lights still lit?

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PARALLEL CIRCUIT Place two bulbs in parallel. What do you notice about the brightness of the bulbs? Place two bulbs in parallel. What do you notice about the brightness of the bulbs? Add a third light bulb in the circuit. What do you notice about the brightness of the bulbs? Add a third light bulb in the circuit. What do you notice about the brightness of the bulbs? Remove the middle bulb from the circuit. What happened? Remove the middle bulb from the circuit. What happened?

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How do we Measure Current and Voltage?

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measuring current Electric current is measured in amps (A) using an ammeter connected in series in the circuit. A

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measuring current A A This is how we draw an ammeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT

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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 V

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measuring voltage V This is how we draw a voltmeter in a circuit. SERIES CIRCUITPARALLEL CIRCUIT V

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OHM’s LAW Measure the current and voltage across each circuit. Measure the current and voltage across each circuit. Use Ohm’s Law to compute resistance Use Ohm’s Law to compute resistance Series Circuit VoltageCurrentResistance VoltageCurrentResistance Parallel Circuit

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measuring current SERIES CIRCUIT PARALLEL CIRCUIT current is the same at all points in the circuit. 2A current is shared between the components 2A 1A

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fill in the missing ammeter readings. ? ? 4A 3A? ? 1A ? 3A 1A

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The circuit is no longer complete, therefore current can not flow The voltage decreases because the current is decreased and the resistance increases.

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The current remains the same. The total resistance drops in a parallel circuit as more bulbs are added The current increases.

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Series and Parallel Circuits Series Circuits Series Circuits only one end of each component is connected only one end of each component is connected e.g. Christmas tree lights e.g. Christmas tree lights Parallel Circuits Parallel Circuits both ends of a component are connected both ends of a component are connected e.g. household lighting e.g. household lighting

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Circuit in Diagram Form _ + battery bulb In a closed circuit, current flows around the loop Current flowing through the filament makes it glow. No Loop No Current No Light current electrons flow opposite the indicated current direction! (repelled by negative terminal)

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copy the following circuits and fill in the missing ammeter readings. ? ? 4A 3A? ? 1A ? 3A 1A

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Different cells produce different voltages. The bigger the voltage supplied by the cell, the bigger the current. measuring voltage Unlike an ammeter, a voltmeter is connected across the components Scientist usually use the term Potential Difference (pd) when they talk about voltage.

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V measuring voltage V V V

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series circuit 1.5V voltage is shared between the components 1.5V 3V

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voltage is the same in all parts of the circuit. 3V parallel circuit 3V

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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.

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Current and Voltage Through a Circuit

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measuring current & voltage V V 6V 4A A A a)

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measuring current & voltage V V 6V 4A A A A b)

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answers 3V 6V 4A 6V 4A 2A 4A a)b)

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