Required practical
Investigating series and parallel circuits
There are different ways to investigate An electrical component that restricts the flow of electrical charge. Fixed-value resistors do not change their resistance, but with variable resistors it is possible to vary the resistance. networks. In this required practical activity, it is important to:
- record The potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). This is the voltage between two points that makes an electric current flow between them. and Moving electric charges, eg electrons moving through a metal wire. accurately
- use appropriate apparatus and methods to measure potential difference and current to work out resistance
Aim of the experiment
To compare the total resistance in A circuit where one component follows directly from another, eg three bulbs in a row with no junctions are said to be connected in series. and In a parallel circuit, the current divides into two or more paths before recombining to complete the circuit. Lamps and other components in these different paths are said to be in parallel. arrangements.
Method:
- Set up the circuit as shown in figure 1, turn the power supply on and close the switch.
- Record the A device used to measure potential difference or voltage. and A device used to measure electric current. readings and calculate the resistance of the resistor using R = V/I, where R is resistance, V is potential difference and I is current.
- Change the resistor and repeat step two to find the resistance of a second resistor.
- Arrange the two resistors in series as shown in figure 2 and close the switch.
- Record the voltmeter and ammeter readings once again and determine the total resistance of both resistors in series using R = V/I.
- Arrange the two resistors in parallel as shown in figure 3 and close the switch.
- Record the voltmeter and ammeter readings once again and calculate the total resistance of both resistors in parallel.
Results
Here are what the results could look like:
| Resistor | Potential difference / V | Current / A | Resitance / Ω |
| R1 | 4.00 | 0.40 | 10 |
| R2 | 4.00 | 0.40 | 10 |
| In series | 4.00 | 0.20 | 20 |
| In parallel | 4.00 | 0.80 | 5 |
| Resistor | R1 |
|---|---|
| Potential difference / V | 4.00 |
| Current / A | 0.40 |
| Resitance / Ω | 10 |
| Resistor | R2 |
|---|---|
| Potential difference / V | 4.00 |
| Current / A | 0.40 |
| Resitance / Ω | 10 |
| Resistor | In series |
|---|---|
| Potential difference / V | 4.00 |
| Current / A | 0.20 |
| Resitance / Ω | 20 |
| Resistor | In parallel |
|---|---|
| Potential difference / V | 4.00 |
| Current / A | 0.80 |
| Resitance / Ω | 5 |
Analysis
- in series, the resistance of the network is equal to the sum of the two individual resistances
- in parallel, the resistance of the network is less than either of the two individual resistances
Evaluation
Placing the resistors in series causes the resistance to be double that of a single resistor because there is only one path for the electrons to follow - the supply must drive current through one resistor and then the other.
Placing the resistors in parallel causes the resistance to be half that of a single resistor.
The outcomes of this experiment are the same using filament lamps, or combinations of resistors and lamps, as the lamps act as resistors.
Hazards and control measures
| Hazard | Consequence | Control measures |
| Heating of wires and resistors | Minor burns | Set up circuit before closing the switch |
| Hazard | Heating of wires and resistors |
|---|---|
| Consequence | Minor burns |
| Control measures | Set up circuit before closing the switch |
