# Current & Voltage In Series Circuits D. Crowley, 2008.

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Current & Voltage In Series Circuits D. Crowley, 2008

Current & Voltage In Series Circuits To be able to explain what happens to the current and voltage in series circuits when more bulbs are added Friday, August 14, 2015

Torch The diagram opposite shows a torch – analyse it, and see if you can work out how it functions You should use all the labelled parts to help in explaining how it works

Torch Key parts: - Both cells are connected, +ve to -ve A spring connects to the - ve of the cell This connects to a switch, on a bent metal strip The switch slides down for ‘on’ This pushes the bent metal strip onto the lamp This completes the circuit, turning the lamp on

Current What is current Current is the flow of electrical charge (electrons) around a circuit Current is measured in amps (via an ammeter) – this must be placed in series with the components +- A

Voltage What is voltage Voltage is the amount of push given to the electrons flowing around a circuit Voltage is measured in volts (via a voltmeter) – this must be placed in parallel with the components +- V

Summary CurrentVoltage Measured inAmps (A)Volts (V) Measured withAmmeter in seriesVoltmeter in parallel Symbol

Experiment 1 Your task is to carry out an experiment to explain what happens to the current in a series circuit, when more bulbs are added Firstly set up an experiment to find out how the current changes from the beginning of the circuit to then end (do this with 1 bulb in the circuit, then 2 bulbs, and then 3 +-+- AA +- AAAA Experiment 1Experiment 2Experiment 3

Experiment 2 Your second task is to carry out an experiment to explain what happens to the voltage in a series circuit, when more bulbs are added Secondly set up the experiment with 1bulb in it, and a voltmeter (across the bulb). Repeat this with 2 bulbs, then 3 bulbs. Finally measure the voltage across the battery +- V +- V V Experiment 1 Experiment 2

+- V +- V V Experiment 1 Experiment 2 +- V +- V Experiment 3 Experiment 4 VV

Current Findings In a series circuit the current remains the same (electrons are never used up, only the energy they carry) The same current flows through all parts of the circuit The size of the current depends on how many components there are (more components = more resistance, so current is lower) E.g. lots of bulbs = lots of resistance, so the current is reduced I = V/R

Current A Current = 10A A Current = 5A If the current is 10A in the first circuit, adding a second bulb doubles the resistance. As it is twice as hard for the electrons to flow around, the current is halved to 5A

Voltage Findings Voltage changes, depending on which component the voltmeter is placed across (because each component has a different resistance) The total voltage of the cell is shared between the components, so adding up the voltage across all the components gives our supply voltage V = I x R

Voltage V VV 6V 2.5V2V 1.5V E.g. cell has a voltage of 6V – adding up the voltage of each component must therefore = 6V

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