Investigating series and parallel circuits

In a nutshell

By using resistors and filament lamps, series and parallel circuits will be tested. This is done by first using a single resistor or filament lamp in series with a cell and then adding an additional component in series or parallel to test how the measured quantities change.

Equations

Word equation	symbol equation
$potential \space difference = current \times resistance$	$V = I \times R$

Variable definitions

quantity name	Symbol	unit name	unit symbol
$potential \space difference$	$V$	$volt$	$V$
$current$	$I$	$ampere$	$I$
$resistance$	$R$	$ohm$	$\Omega$

Equipment list

The following equipment list can be used to conduct the experiment to investigate series and parallel circuits.

Equipment	Use
Digital ammeter	To measure the current in the circuit.
Digital voltmeter	To measure the potential difference across components.
Fixed resistors ( $\times2$ )	To provide a resistance across the circuit.
Filament lamps ( $\times2$ )	To provide a resistance across the circuit.
Connecting leads	To connect each element of the circuit together.
Battery or suitable power supply	To provide power to the circuit.

Experimental variables

The independent variable is the variable you change. The dependent variable is the variable that changes depending on the other variables, and is the one you measure. The control variables are the variables that are kept constant.

Independent variable	$Configuration\ of\ resistors$
Dependent variable	$Potential\ difference,\ V,\ and\ current,\ I$
Control variable	$Potential\ difference\ of\ power\ supply,\ use\ of\ the\ same\ equipment$

Safety precautions

When performing experiments, it is very important to consider safety precautions. This is so that no one gets hurt or injured during the experiment.

Hazard

risk

Safety measure

Hot wires

The resistance can cause the wires used in the circuit to heat up. These can cause burns if touched.

Do not touch the wires directly if the circuit is switched on or has just recently been turned off. Switch off the power supply if burning can be smelled.

If burnt, run the burn under cold water for five minutes.

Liquids spilled onto circuit

Liquids can damage the electrical equipment and may cause a fire.

Make sure there are no liquids close to the electrical equipment.

Method

These are the instructions to complete the experiment. Record all measurements taken as you work through the experiment in a table.

Physics; Physics practicals; KS4 Year 10; Investigating series and parallel circuits

A.	Ammeter
B.	Power supply
C.	Resistor
D.	Voltmeter
1.	Series circuit
2.	Parallel circuit

1.	Use the diagram to set up your circuit diagram as shown, with a single fixed resistor $R_1$ .
2.	Switch the power supply on and record the readings on the ammeter and voltmeter. Make sure to switch off the power supply when adding and removing components from the circuit.
3.	Replace the first resistor with the second resistor $R_2$ and record the readings on the ammeter and voltmeter.
4.	Arrange the two resistors in series, as shown above. Repeat step 2.
5.	Arrange the two resistors in parallel, as shown in above. Repeat step 2.
6.	Repeat the experiment from step 1, instead using filament lamps instead of fixed resistors. Use a separate table of results for this.

Analysis

This is how you will use the data recorded to form conclusions.

1.

Calculate the value of resistance, $R$ , for each pair of measurements for voltage and current. This can be done using a rearranged form of Ohm's law.

V = I \times R \to R = \dfrac{V}{I}

2.

Compare the results for series and parallel circuits, for both the fixed resistors and the filament lamps. Use your knowledge of how total resistance of a circuit is affected by its circuit type.

For series circuits:

R_{total} = R_1 +R_2

For parallel circuits:

\dfrac{1}{R_{total}} = \dfrac{1}{R_1} + \dfrac{1}{R_2}

Conclusion

For the series circuit, the total resistance should be equal to the sum of the resistance of the two individual resistors (the fixed resistors or the filament lamps). For the parallel circuit, the total resistance should be less than either of the two individual resistances.

Evaluation

Once you have completed your experiment, it is important to consider how it could be improved. You should come up with ways to improve the accuracy of your values. If you got a result that seems unreasonable, think about why this was.