Modelling Electric Circuits

Electricity is something that students encounter every day of their lives. However, there tend to be lots of misconceptions and these are best addressed at Key Stage 3 and GCSE by using models and analogies to explain what are otherwise abstract concepts.

Below are four methods of modelling electric circuits but it is important to remember that not all of them need to be used at once and that their value lies not only in students identifying the ways in which they work well but also in evaluating their limitations.

Hula hoop model

pink-hoop

Students sit in small groups (4-5 students) and hold a plastic hula hoop (or loop of rope) loosely in their hands. One of the students acts as the cell / power supply and begins to turn the hula hoop in one direction. The main message here is that the current moves at all points at all times in a circuit (a common misconception is that the current starts at the cell and slowly makes its way in procession through the wire).

The students will also feel some heat from the friction of the plastic hula hoop as it passes through their hands. This demonstrates that energy is being transferred but that the electrons themselves are not being used up (another common misconception). This model can also be used to introduce resistance i.e. for a given power supply, a higher resistance (i.e. a tighter grip on the hula hoop) will result in a lower current.

Student electron model

A student plays the part of the cell / power supply with a big plus sign on their right shoulder (positive terminal) and a big minus sign on their left (negative terminal). The remaining students are electrons and should arrange themselves in a tight circle (the circuit) around the edge of the classroom. Remind the students that electrons are negatively charged and, as such, repel each other (so they need to spread out evenly rather than clump together).

The student (electron) nearest the ‘positive terminal’ is pulled into the ‘cell’ and then pushed (gently!) out of the ‘negative terminal.’ As a result, this student will bump into / move close to the student standing next to the ‘negative terminal’ who, in turn, will be repelled and move away. This repulsion is repeated all the way around the classroom until a new ‘electron’ is pulled into the ‘cell’ at the ‘positive terminal.’ The whole process should be repeated and sped up to create a giant electric circuit.

Highlight that the push or shove from the ‘cell’ represents the voltage. The more powerful the cell, the bigger the voltage it gives to each electron. Finally, model resistance by placing two rows of chairs, through which the students have to squeeze, along one side of the classroom. As with the hula hoop model, the students should see that in a series circuit, if they are slowed down in just one small section of the circuit the current is reduced everywhere.

Bank and shop model

As above, the students should arrange themselves in a tight circle around the classroom. One student is the ‘bank’ (cell / power supply) and another is the ‘shop’ (bulb) which is located someway further down the road. At the bank, each student is given ten pounds (use Monopoly money) which they must then spend in full at the shop and therefore return to the bank with nothing (herein lies one limitation of the model as some energy is required for the current to get back to the battery).

monopoly

Next, pretend there are two bulbs in series of equal brightness or, in other words, two neighbouring shops in which each student spends an equal amount of money (the ‘bank’ should give each student ten pounds in two £5 notes in order to model this). Extend the activity by asking the students to model what would happen if there were two bulbs of different brightness or how the model would differ in a parallel circuit.

Mini whiteboards and sweets

Before building electric circuits, it can be useful for students to draw circuit diagrams on mini-whiteboards and then use sweets to demonstrate what is happening at each component. For example, if each sweet represents 1 V and the students are using a 6 V cell then they should start with just six sweets. If there are two bulbs in series but one is twice as bright as the other, how many sweets (volts) does each bulb require? Again, extend this activity by asking students to consider what would happen in different series and parallel circuits.

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