# Year 7 circuit models

Discussion in 'Science' started by blazer, Jun 12, 2011.

1. ### blazerStar commenter

I've not used this model but I suppose the hill you go up at the start represents the cell that provides the 'push'. The car represents the current flowing and the energy of that current gets 'used up' (transfered) as the car goes round the track until the curent gets back to the start when it needs another 'push' from the battery to go round again. You can get those small rollercoacter toys (some have little penguins).
http://enablingdevices.com/catalog/toys_for_disabled_children/slide-toys/penguin-roller-coaster

Or could you get one of those matchbox hotwhhels type tracks that were popular in my childhood. They had an electric or spring pwered booster that shot the cars round the rack.
http://direct.tesco.com/q/Ne.758/N.1999244\$3998462/Nr.99.aspx?gclid=CKez7p3csKkCFcod4QodtGnTLQ

2. ### physics_suits_you

It's fair, but what do the "uphill" sections of a rollercoaster represent?
Better (?) is the ski lift model - the lift (power supply) gives the skiers (electrical charges - do they need to know about electrons at Y7?) energy, which is then dissipated as they descend the slope (pass through components). Big differences in (potential) energy [height] represent big changes in voltage (potential difference). Flat sections have no energy change, so represent connecting wires. The total number of skiers passing any point is constant (unless some break their legs = limitation of models = high level thinking). 2 different "runs" could represent parallel branches.
You may have a "water" model where pupils can see the water flowing through plastic pipes and can appreciate how turning the voltage up on the pump results in a bigger current. They can also see the effect of narrower pipes, or parallel tubes.
Please check what you are required to teach. Current should have been considered in KS2, and voltage may not be needed until Y9. A thorough understanding of the heirarchy of concepts is better than rushing in to quite complex relationships, especially when resistance is introduced as a quantitative rather than a qualitative idea.

I recently went to a (very good) Institute of Physics talk on how best to model circuits. To summarise, it seems the best solution is to have 2 models. One for Current & resistance & one for pd or voltage.
Current: Model of marbles in a pipe. There is no space between the marbles, the pipe's diameter is the same as the diameter of the marble and the circuit is just 'full' of marbles from the +ve t o the -ve terminal. When the battery gives them a push, all the marbles move along simultaneously wherever they are in the circuit (since they are touching, they all experience the push at the same time). This helps pupils visualise the idea that current is the same around a series circuit - wherever you decide to measure, the number of marbles passing a given point is the same.
Resistance: Consider a very 'sticky' part of pipe with lots of friction - the marbles slow down & the battery has to push a bit harder to get the current or marble flow back up to speed. ALL the marbles are slowed down, not just the ones in the pipe, since they are all lined up one in front of another.
Voltage: You need to change the model a bit here (and the model has flaws) - now the marbles represent electrons more specifically. The battery gives each marble / electron some energy which makes the marble 'jiggle about' as it travels through the pipe / circuit. When the marble reaches a component some or all of this 'jiggling energy' is given to the component which uses it to light up / get hot. The marbles carry on through the pipe with reduced 'jiggling energy'. Measuring the pd across a component is like measuring the amount of 'jiggling energy' lost to that component. This model does not cope with how the electrons 'know' how much pd to drop across each component - something I am often asked.
Hope this helps.

4. ### Star_TeacherNew commenter

so the yearly LO for yr 7 concerning circuits is:
"describe how energy is transferred in simple contexts such as heating
and cooling, food chains and simple circuits"

So the key idea about simple circuits is one of electrical current being a transfer of energy. Students do not need to know that current involves electrons just yet, just that it is a transfer of energy from the cell to the components. The speed that the energy is transferred is the current, and the voltage is the amount of energy that is being transferred.

The way i have demonstrated this in the past is to get a large loop of string (so that students can all hold on to it), now the teacher can act as a cell and start to pull in one direction on the string causing it to move around, it has a set speed and the energy used to pull the string is set. Now if you want to extend this model, you can start to add additional cells and components, a cell would be a student helping you to pull the string in one direction and a component would lightly grip the string hindering the speed of the string, I like to make this elaborate by making the component and cells wear hats to signify what they are. You could then use this to work up to resistance, but for year 7 I dont think this is necessary.

Hope this is useful, any comments let me know

5. ### outstandingwinger

I find it easier now to dispense of all models with simple circuits to be honest and teach the circuits as puzzles with a set of rules to solve them, with proper definitions of current, voltage etc. The models really don't help I find and lay down more misconceptions than they are worth.
I've spent many years teaching models for this and none of them have led to a deep understanding of what is going on.

6. ### blazerStar commenter

Wow, what a good idea. I am going to pinch this and give it a whirl.