Required practical - investigate resistor networks

There are different ways to investigate resistor networks. In this 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

Figure 1

Figure 2

Aim of the experiment

To compare the total resistance in series and parallel arrangements.

Figure 3

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 an ammeter readings once again and calculate the total resistance of both resistors in parallel.

Results

The results could look like this:

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.

Suggest a reason why placing the resistors in parallel causes the resistance to be half that of a single resistor.

Hazards and control measures