understanding a series circuit
DESCRIPTION
Understanding a series circuit. You can think of a circuit as a circular motorway …. … a bit like the M25. Along this circular road, cars (called ‘Q’ cars) slowly travel bumper-to-bumper all the way around …. … a bit like the M25. A break in the road anywhere in the loop …. - PowerPoint PPT PresentationTRANSCRIPT
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Understanding a series circuit
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You can think of a circuit as a circular motorway …
… a bit like the M25
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Along this circular road, cars (called ‘Q’ cars) slowly travel bumper-to-bumper all the way around …
… a bit like the M25
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A break in the road anywhere in the loop …
… will mean all the cars stop moving.
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If a bulb breaks or is taken out – it creates a break in the circuit. This will stop all the cars, like a switch.
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Understanding a series circuit
Potential differenceand
Current
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A petrol pump gives some energy to the cars, so they can drive round.
The cell in an electrical circuit acts a bit like an energy pump.
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We can measure the petrol difference before and after they visit the pump …
… we call this the potential difference (measured in Volts).
It tells us how much energy is being transferred to the circuit.
P D
V6V
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We can also measure how many ‘Q’ cars cross a particular point in the road every second …
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The number of ‘Q’ cars each second tells us the flow of cars …
A
… this is the current (measured in Amps).It tells us how quickly electrical charge is flowing in the
circuit.
3A
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Understanding a series circuit
Resistanceand
Lamps
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We can measure how many ‘Q’ cars cross a particular point in the road every second …
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If the cars meet a resistance in the road, the cars will slow down …
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Because the cars are bumper to bumper …
… the resistance will slow down all the cars in the circuit.We measure resistance in Ohms.
3 Ohms
A 2A
A
2A
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The bigger the resistance, the slower the cars will go …
The number of ‘Q’ cars per second will get smaller …The current (Amps) decreases.
6 Ohms
A 1A
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An enterprising thief can take petrol from the cars as they slow down …
… leaving just enough for the cars to get back to the petrol pump.
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The thief uses the stolen petrol to burn in a barrel …
… this gives out light and heat.
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… by stealing petrol, the thief takes some energy from the cars as they pass – like a lamp in a circuit.
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… we can measure how much energy is taken by measuring the petrol difference before and after the cars
pass the thief.
V
P D
6V
6V
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If there are two thieves, they will have to share the petrol they steal from the cars as they pass …
… they have to leave enough petrol for the cars to get back to the pump.
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… each thief can only take half as much petrol, so his fire burns less bright.
The energy transferred to each bulb will be halved.
V
P D
6V
3V
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This means each thief can take more petrol from the cars again. So the bulbs will be brightly lit again.
6V 6V
6V 6V
… we could add another petrol pump, to give the cars more
energy.
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We can measure the flow of cars with one bulb.
A 3A
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… each extra bulb creates more resistance and will slow down the flow of cars. Reducing the current.
A 1.5 A
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Understanding a parallel circuit
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In a parallel circuit, the road splits creating two loops …
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A break in a loop stops cars from moving in that loop …
… but they can use the other loop to travel back to the pump.
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But, a break that prevents cars getting to the pump …
… will stop all of the cars in the circuit.
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Understanding a parallel circuit
Current and
Resistance
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All the cars leave the petrol pump …3 Ohms
3 Ohms
The traffic cop will see the full number of cars per second (e.g. current 2A)
Loop A
Loop B
A 2A
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At the junction, the road splits – and half the cars go along each loop. 3 Ohms
3 Ohms
The traffic cop will see half the number of cars per second in loop A (e.g. current 1A)
Loop A
Loop B
A1A
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The other half of the cars along the other loop …3 Ohms
3 Ohms
The traffic cop will see half the number of cars per second in loop B (e.g. current 1A)
Loop A
Loop B
A
1A
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All the cars must come back to the petrol pump …3 Ohms
3 Ohms
The traffic cop will see the full number of cars per second again (e.g. current 2A)
Loop A
Loop B
A2A
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Some loops may have more resistance than others …
Cars prefer to take roads with less resistance …
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If one loop has more resistance than another …3 Ohms
6 Ohms
The cars will still divide up between the two loops, but more will travel along the loop with less resistance.
Loop A
Loop B
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All the cars must travel via the pump …3 Ohms
6 Ohms
The traffic cop measures 3 ‘Q’ cars per second; a current of 3 Amps
Loop A
Loop B
A3A
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If loop A has half the resistance of loop B …3 Ohms
6 Ohms
… then for every 2 cars per second that travel along loop A …
Loop A
Loop B
A2A
A3A
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If loop A has half the resistance of loop B …4 Ohms
8 Ohms
… only 1 car per second will travel along loop B.
Loop A
Loop B
A1A
A3A
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Whichever loop they took - all the cars must travel back to the pump …
4 Ohms
8 OhmsLoop A
Loop B
A1A
A3A
A2A
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Understanding a parallel circuit
Voltageand
Lamps
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An enterprising thief can take petrol from the cars as they slow down …
… leaving just enough for the cars to get back to the petrol pump.
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With only one thief in each loop, each thief can take full amount of petrol from each car as they pass.
Loop A
Loop B 6V
6V
6V
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If there are two thieves in the same loop, they will have to share the petrol they steal from the cars as they pass …
… they will only get half the petrol they would have on their own.
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Thieves in the same loop have to share petrol. The thief in his own loop gets all the petrol to himself.
Loop A
Loop B 6V
3V
6V
3V
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Try some practice questions
http://www.bbc.co.uk/bitesize/ks3/science/energy_electricity_forces/electric_current_voltage/quiz/q74171589/
http://www.twothirtyvolts.org.uk/education/revision-quiz/electric-circuits-11to14.html
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Understanding circuits
Formula triangles
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The energy transferred by each ‘Q’ car.
The number of ‘Q’ cars that pass a point each second.Roadworks slow the flow of cars.
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The brightness of the bulb depends on how much energy is transferred each second… that is how much petrol can the thief steal each second
Power (Watts) = energy transferred each second (J/s) = current x voltage
Brightness of the bulb = The number of cars passing each second x the amount of petrol the thief can take from each car.