Current & Voltage In Series Circuits

D. Crowley, 2008

Current & VoltageIn Series Circuits To be able to explain what happens to the current and

voltage in series circuits when more bulbs are added

Wednesday, April 19, 2023

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

TorchKey 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

CurrentWhat 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

VoltageWhat 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

Current Voltage

Measured in Amps (A) Volts (V)

Measured with Ammeter in series Voltmeter 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

+ -

AA AA

Experiment 1 Experiment 2 Experiment 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

Experiment 2+ -

V

+ -

V

V

Experiment 1 Experiment 2

+ -

V

+ -

VExperiment 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