Electrical Circuit
Electricity and Magnetism

From rope loop to electric circuit model

Classroom Activity for 11-14 Supporting Physics Teaching

What the Activity is for

The rope loop is presented as a teaching model, which provides a way of helping pupils develop an understanding of abstract concepts (such as charge, current, resistance) by relating them directly to the movement of a length of rope around in a loop.

Notice how the same things are happening as in the electric circuit: a chemical store is being emptied (teacher as battery), and at a distance, something is getting warmed up (pupil as bulb).

What to Prepare

  • a long length of rope (6–9 millimetre diameter is ideal)

What Happens During this Activity

To introduce the rope loop model to the pupils the class is organised to stand in a big circle (you might carry out this activity in the school hall or outside) and the rope loop is passed out with each pupil allowing it to pass lightly over their curled fingers. The teacher (or nominated pupil) then starts to move the loop of rope round by passing it from hand to hand.

One pupil is instructed to grip the rope a little more tightly as it passes through their hand, and the teacher keeps the rope moving.

We have found it very effective to engage the pupils in this activity with little or no introduction, and then at this point (with the basic rope circuit set up) the teacher starts to pose questions:

Teacher: So! What has this to do with electric circuits? Any ideas?

The key features of the model to establish are that:

  • The battery is represented by the teacher moving the rope.
  • The bulb is represented by the pupil gripping the rope.
  • The electric current (or moving charged particles) is represented by the moving rope.
  • Energy is shifted through working (due to friction) at the bulb.

Using the rope loop to establish the key features of the electric circuit model

The rope loop can now be used to consolidate the key features of the electric circuit model:

The charged particles originate in the circuit

Teacher: Now it's very clear. The rope isn't coming from me. I'm just making it move around. In just the same way, the charged particles don't come from the battery. It just makes them move around the circuit.

The charged particles all around the circuit are set into motion together

Teacher: Look everybody! As soon as I set the rope moving here, it starts moving all around the loop. In just the same way, as soon as the circuit is completed, the charged particles start moving in all parts of the circuit.

Current the same in each part of the loop

Teacher: The same amount of rope returns to me as leaves me every second. The rope does not get used up or disappear on the way round. In just the same way, the charge does not get used up on the way around the circuit, so the current is the same everywhere.

Energy is shifted where there is resistance

Teacher: Now Julia can feel her hands warming up because she is gripping the rope. There is warming due to the effect of friction as the rope passes through her fingers. No-one else feels any real heating effect because they are not resisting the movement of the rope.

We'd suggest that you link this back to the big circuit!

The point to make here is that it just does not matter how big the circuit is – unless it crosses the Atlantic!

As soon as the charged particles start moving energy is shifting from store to store.

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