Practical activity

This practical activity consists of three tasks. The first is to explore how resistors in series work to control current flowing in an electrical circuit, the second is to explore how resistors in parallel work to control current flow and the third is to examine how the resistance of nichrome wires is determined by length and diameter.

Task 1

Your first task is to investigate resistors in series.

Before you enter the experiment, read these instructions thoroughly. When you are ready, enter the experiment using the first option ‘Resistors in series’. You are provided with a range of resistors with known resistances, 4 resistors (a) to (d) with unknown resistances and a piece of bare wire (Figure 5).

Figure 5. Resistors and a piece of bare wire located in the Electrical Circuits application.

You can find the stated resistance value for each resistor by placing the cursor over a resistor or by using the four-band colour code. Note that some stated values are expressed as kiloohms (1 kΩ = 1000 Ω) and megaohms (1 MΩ = 1000000 Ω). Before we explore how resistors work in series, we will examine each resistor to check that the stated value is correct.

In your laboratory notebook make a table with the following headings (Table 1).

Voltage (V)

Current (A)

Stated resistance (Ω)

Measured resistance (Ω)

Table 1 Laboratory notebook headings for examining a single resistor.

• Now choose a battery (you have a choice of either a 1.5 V or 9 V battery).
• Select a resistor with a stated resistance and place it into one of the two slots.
• To complete the circuit, you will need to place the bare wire into the second unfilled slot.
• Now close the switch and record the voltage across the resistor and the current flowing in the circuit (the switch will open automatically after a few seconds).
• Repeat this procedure for five other resistors with stated resistances.

To check the stated resistance values against the measured values you will now use Ohms’ law to calculate the measured resistance for each of your resistors.

Note: the ammeter provides the current in amperes (A), but it uses metric notation, such that 0.1 A is represented as 100 milliamperes (mA), 0.0001 A is represented as 100 microamperes (µA).

Based on your observations, how well do the measured resistance values compare with the stated values?

The resistors have a gold band tolerance rating which means your measured values should fall within a range that is ±5% of the stated resistance.

Now that you are familiar with using the application and Ohm’s law to calculate resistance, repeat the above process using the resistors with unknown values (resistors (a) to (d)) to calculate their measured resistance values and discuss your findings with your classmates.

Your next step is to look at how resistors work in series to control current flow. Copy Table 2 into your laboratory notebook.

Voltage (V)

Current (A)

Stated resistance for resistor 1 (Ω)

Stated resistance for resistor 2 (Ω)

Measured resistance (Ω)

Table 2 Laboratory notebook table headings for examining resistors in series.

• Once again choose a battery (you have a choice of either a 1.5 V or 9 V battery).
• Select a resistor with a stated resistance and place it into one of the two slots.
• To complete the circuit, place a second resistor into the second unfilled slot.
• Now close the switch and record the voltage across the resistors and the current flowing in the circuit (the switch will open automatically after a few seconds).
• Repeat this procedure for five other pairings of resistors with stated resistances.

Now use Ohm’s law to calculate the measured resistance in the circuit for each of your resistor pairings and discuss your findings with your classmates.

Task 2

Your second task is to investigate resistors in parallel.

Before you enter the experiment, read these instructions thoroughly. When you are ready, enter the experiment using the second option ‘Resistors in parallel’. Once again, copy the following table headings into your laboratory notebook (Table 3).

Voltage (V)

Current (A)

Stated resistance for resistor 1 (Ω)

Stated resistance for resistor 2 (Ω)

Measured resistance (Ω)

Table 3 Laboratory notebook table headings for examining resistors in parallel.

• Once again choose a battery (you have a choice of either a 1.5 V or 9 V battery).
• Select a resistor with a stated resistance and place it into one of the two slots.
• Select another resistor and place it into the second slot.
• Now close the switch and record the voltage across the resistors and the current flowing in the circuit (the switch will open automatically after a few seconds).
• Repeat this procedure for five other pairings of resistors with stated resistances.

Now use Ohm’s law to calculate the measured resistance in the circuit for each of your resistor pairings and discuss your findings with your classmates.

Task 3

Your third task is to investigate the resistance in a wire.

Before you enter the experiment, read these instructions thoroughly. When you are ready, enter the experiment using the third option ‘Resistance in a wire’. This experimental set-up is different to those you used in Tasks 1 and 2 (see Figure 6). Here you are given the choice of three 1 m lengths of nichrome wire of varying thickness.

Figure 6 The experimental set-up for measuring the resistances of nichrome wires. In this illustrated example, the thick wire has been placed into the circuit and the crocodile clip has been used to close the circuit at 70 cm.

Copy Table 4 into your laboratory notebook.

Chosen wire

Length (cm)

Voltage (V)

Current (A)

Measured resistance (Ω)

Table 4 Laboratory notebook table headings for examining resistance in a nichrome wire.

In Tasks 1 and 2 the voltage across the resistor was stable, however in this task the voltage will vary depending on the load on the battery – the current flowing in the circuit.

• Select a nichrome wire and drag it into the slot at the bottom of the electrical circuit.
• Use the crocodile clip to close the circuit, starting at 90 to 100 cm – use the zoom view to accurately record the length you’ve selected.
• Turn on the switch and record both the voltage and current.
• Now move the crocodile clip 10 to 15 cm further down the length of the wire, turn on the switch and record the voltage and current readings.
• Repeat this process several more times – beware, at shorter lengths the nichrome wires will start to heat up and your recordings will be compromised.

Once you have recorded your observations, use Ohm’s law to calculate the measured resistances for each length of the wire and repeat the process until you have examined all three wires.

Now that you have data for each wire. Plot resistance against length for each wire on the same graph and fit a best fit line to each data set.

Discuss your findings with your classmates.

Resistance

Click on the icon below to access the Electrical circuits application homepage in the OpenSTEM Africa Virtual Laboratory. Watch the introductory video before entering the experiment.

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