Misconceptions: Electrical Circuits 2

My second post in the electrical misconceptions series relates to the use of terms in this topic.

The topic of electricity contains several abstract terms; voltage, current, resistance, energy, power etc. and students have understandings of some of these terms (current and resistance) from other areas of their lives. The other terms are more abstract because students often do not have a clear understanding, or framework or visual representation of what they mean. Of course, the terms that they have some kind of context for (current and resistance) may actually be leading to a further misconception because the meaning may vary in alternative contexts.

Quick explanations of each term

  • Electricity: The name of the topic. Electricity as a quantity or substance doesn’t exist.
  • Voltage: A measure of how much charges are pushed from one point to another.
  • Current: A measure of how fast charges are moving
  • Resistance: Anything that limits the push (voltage) from moving the charges (current). It is an opposition to the free movement of charges.
  • Energy: A measure of the effect that moving charges have on the circuit e.g. perhaps the moving charges cause a heating effect or a chemical change to occur or some other form of energy to be expressed by the movement of charges.
  • Power: A measure of how quickly the energy is given out or changed between forms.

 

I Still Have No Idea What This is All About! **Analogy Time 1 – The BIKE CHAIN**

Bike_Chain_1

I think of the charges in the circuit as being connected, like the links on a bike chain.

  • All of the charges already exist in the circuit before the battery or power pack is connected, but the charges don’t move [no battery = no voltage = no moving charges]
  • Connecting up the battery is analogous to peddling on a bike. Peddling causes the bike change to rotate. [Connecting battery means there is a voltage. Voltage makes the charges flow]
  • If you were then to gently squeeze the breaks, while trying to peddle at the same time the bike chain would rotate slower [Adding resistance means that the current travels slower even with the same current]
  • BUT, applying the breaks gently will increase friction between the break pads and the wheel and heat will be produced. [The flowing current will create a heating effect, or some other expression of energy]
  • The energy converted per second is the power

Obviously this analogy isn’t perfect, but it explains what happens in a real-world context and takes away the unknown or un-experienced element to electricity terms.

 

**Analogy 2 – Pass the water buckets, there’s a fire**

bucket-brigade

In the pre-fire department days communities banded together to put out fires by forming a human loop between the fire and a water source, passing buckets filled with water to one another to quench the fire. The people represent the wire in the circuit in this case.

  • If the fire is small, the people can pass the buckets relatively slowly around the loop. If the fire is larger then the people need to pass the buckets faster [The fire is the drive (voltage) behind how quickly the buckets (current) move]
  • If one person can only hold one bucket at a time, then a slower worker will take longer to pass his bucket to the next person. This slows down the flow of the buckets through the loop. [Bigger resistance affects everything in the circuit and opposes the flow of current even though though the fire (voltage) is at a set amount]
  • People around this slower worker get angry and frustrated at him/her. [This frustration is similar to energy being created by particles experiencing a resistance]

Another benefit of using this analogy is that the flowing charge (the buckets) are filled with water until the water is discharged into the fire. We could use this to describe that the flow of current carries energy, which is lost or decreased when the current passes through a component in the circuit. So, even though the current flow is continuous around the circuit, some of the energy carried by the current is lost at different parts of the circuit.

In the language of the analogy, the buckets are passed around the human circuit. Some water (energy) is spilled as they are passed through the circuit. Also, a lot more energy (most of the water in the buckets) is lost when it passes through the part of the circuit with the component in it (the fire in this case).

 

Is that all?

Remember that not all analogies are perfect and have flaws that will need to be addressed. So have a think about each of the above analogies and your understanding of what happens when a single bulb is connected to a battery. Which analogy makes sense? Do either of them have any benefit? Can you think of another analogy? Or does your understanding differ completely from these? Post your thought in the comments.

 

Final point

Learning something like the topic of electricity is difficult and having a visual representation can help you immensely. But a single visual representation would probably not be enough for you fully understand the intricacies of electrical systems.

So, I’d recommend that you check out a few Youtube videos, the PHET electrical circuits applet and to pester your teacher until you have a solid view of what’s going on.

Remember, it’s your education – so take responsibility for it!

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