Required practical - investigating series and parallel circuits

There are different ways to investigate resistor networks. In this required practical activity, it is important to:

  • record potential difference and current accurately
  • use appropriate apparatus and methods to measure potential difference and current to work out resistance
Circuit with a switch, battery, ammeter and one resistors in series with a voltmeter in parallel to the resistors.Figure 1Circuit with a switch, battery, ammeter and two resistors in series with a voltmeter in parallel to the resistors.Figure 2Circuit with a switch, battery, ammeter and two resistors in parallel with a voltmeter in parallel to the resistors.Figure 3

Aim of the experiment

To compare the total resistance in series and parallel arrangements.

Method:

  1. Set up the circuit as shown in figure 1, turn the power supply on and close the switch.
  2. Record the voltmeter and ammeter readings and calculate the resistance of the resistor using R = V/I, where R is resistance, V is potential difference and I is current.
  3. Change the resistor and repeat step two to find the resistance of a second resistor.
  4. Arrange the two resistors in series as shown in figure 2 and close the switch.
  5. Record the voltmeter and ammeter readings once again and determine the total resistance of both resistors in series using R = V/I.
  6. Arrange the two resistors in parallel as shown in figure 3 and close the switch.
  7. 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:

ResistorPotential difference / VCurrent / AResitance / Ω
R14.000.4010
R24.000.4010
In series4.000.2020
In parallel4.000.805

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

HazardConsequenceControl measures
Heating of wires and resistorsMinor burnsSet up circuit before closing the switch