Resources:
Method 1: meter ruler with a thin uninsulated wire secured to it with masking tape (copper or constantan); connecting wires; crocodile clips and an ohmmeter.
Method 2: meter ruler with a thin uninsulated wire mounted to it with masking tape (copper or constantan); connecting wires; crocodile clips; 2 cells; voltmeter and an ammeter.
Method 3: meter ruler with a thin uninsulated wire mounted to it with masking tape (copper or constantan); connecting wires; crocodile clips; 2 cells and a 1.5V bulb.
Handout: Questions related to the Mission Assignment and space for the students to draw their diagrams.
Electrical resistance is not covered in KS2, so use the starter task and presentation to introduce the topic.
Ask students if they think it is easier to blow through 10 straws in a bunch or 10 straws connected end to end. After a discussion, the students can try this for themselves. However, it may be easier to manage with less straws or a demonstration.
Answer questions and take part in activities during the presentation.
Here are some practical demonstrations you could use to model resistance:
Act it
Get the students to line up in three rows close together with one student stood at the side. The group of students will represent the wire and the other student an electron. For this task, the students should reset to their original positions after each trial.
The electron walks through the wire from one side to the other. The group of students stands still and allows the electron to pass. Then, repeat the same trial, but with the wire’s length cut in half (ask half the group to step away, making the wire shorter).
Reset: The electron walks through the wire from one side to the other. The group of students stands still and allows the electron to pass. Then, repeat the same trial but with the wire becoming wider (ask the group to move slightly outward, giving the electron more space).
Reset: The electron walks through the wire from one side to the other. The group of students stands still and allows the electron to pass. Then, repeat the same trial but with the molecules they are representing as hot (ask the students to keep their feet still and arms by their side but jiggle on the spot).
After each trial, ask the electron which one was easiest. The easier tasks have the least resistance.
Make it
The task above can also be recreated using tennis balls and a stocking or pair of tights. Cutting off the toe of the stocking, you can drop tennis balls through and see how easy it is. For the first trial, shorten it; for the second trial stretch it wider and for the third trial jiggle the tight. It is worthwhile putting multiple tennis balls in to create the effect of a current.
Career Film: Take a tour around Rolls Royce SMR's Heritage Museum in Derby to find out about Scott Barham's job. Scott works as the Chief Design Engineer for Rolls Royce SMR.
Expert Film: This is Scott Barham. Scott works as the Chief Design Engineer for Rolls Royce SMR. Listen to Scott as he explains the causes and effects of electrical resistance.
In this experiment, the students will be measuring the resistance of a wire when they vary the length. Three methods can be used, depending on what equipment is available.
Method 1 measures resistance using an ohmmeter. Method 2 requires a voltmeter and an ammeter so the resistance can be calculated. Method 3 asks students for a qualitative description of the brightness of a bulb.
Method 1 is the recommended method. See the handout for full details.
Support: The teacher models the practical setup to the class. The students take turns to set up the practical in front of the class and take readings before they work independently.
Challenge: The students use their data to make predictions for the resistance readings if the wires were made longer, thicker, thinner or from a different material.
Have students work in pairs or small groups to answer the following questions:
After giving students a few minutes to discuss and answer these questions, you can then ask for volunteers to share their answers with the rest of the class.
Electrical resistance is a measure of how much current is restricted. It is measured in ohms and given the symbol Ω (omega – a Greek letter). The resistance in a wire is affected by four key properties (although only the first three are relevant in this lesson).
Length – the longer the wire, the higher the resistance. This is because the current has further to travel and this requires more effort.
Width (cross-sectional area) – the wider the wire, the lower the resistance. This is because electrons have more possible routes to travel and therefore it is easier.
Temperature – the hotter the wire, the higher the resistance. This is because as the wire increases in temperature, particles vibrate and move more, restricting the ease at which electrons can flow. A thermistor is a component where the inverse is true.
Resistivity (stretch and challenge) – this is a physical property of the material that allows current to flow. For example, copper has a low resistivity as it allows current to flow easily, whereas plastics have a very high resistivity as they do not let current flow (they act as an electrical insulator).
A scientific model is any analogy, physical or theoretical, that can be used to describe, explain or predict a scientific phenomenon.