After recapping how to build a simple circuit (which they did independently, MashaAllah), I asked them where the energy in the circuit was coming from? They answered the battery.
I told them even though we call an AA battery a battery, it's actually just a cell, i.e. one part of it. When you have more than one cell together (hold up two AA batteries) then it's called a battery. So the AA batteries we use are actually called "single-cell batteries" because they only have one cell inside them. 😎
So looking at our circuit, how many cells does it have? One. And is the bulb shining very brightly? Not really... So how do they think we could make it shine brighter? F answered straightaway to add more cells. 👍 So I asked them to work together to build a circuit with one bulb and two cells, since at the moment they had a circuit with one bulb and one cell each. After a little arguing (lol) they managed and were pleased to see the bulb light up brighter! 💡
So I asked does that mean that if I keep on adding cells, making a bigger and bigger battery, then the bulb will keep on shining brighter and brighter? Or would something else happen? At first they laughed that it would, but then M said no because if you had too much power then the bulb would catch on fire. 😂
We read the page about how bulbs work in our KS1 Electricity book and then looked at one of the bulbs closely to see if we could see the filament (it was a little difficult so was there anything we could use to make it look bigger? A magnifying glass!). It was easy to see the filament when the bulb was on though, so need for a magnifying glass there! We talked about how the filament makes both light and heat (they touched the top of the bulb whilst it was lit up and compared it to what the top of a bulb which was off felt like) and how the filament can melt/the bulb "pops" - which is why we need to change the light bulbs in our house sometimes.
So if adding more cells to a circuit would make the bulb shine brighter (to a point!) then what would happen if we added more bulbs to a circuit, but kept the number of cells the same?
I asked the girls to help me design an investigation to find out, making sure we did things scientifically so everything was fair!
As they aren't expected to learn circuit diagrams at this stage, and to avoid overwhelming and complicating things, I had them draw the circuits pictorally instead.
So their prediction was that the energy from the battery would be shared equally between the bulbs... So when we tested it and only one bulb came on they were confused! We switched the bulbs in the bulb holders around to make sure it wasn't the bulbs which were broken and that it really was just one of the bulbs lighting up, then I drew a diagram of the three bulb series circuit on the board so we could talk about what we'd seen.
I asked the girls if they thought they could explain their conclusion, using what they know about the power in a circuit. F said the first bulb had used up all the energy so there was none left for the other bulbs to light up. So I asked them if that meant all the electricity had stopped at the first bulb? First they said yes, then they thought about it and said no - because if it had stopped at the first bulb then it wouldn't have carried on to make a loop and the circuit wouldn't have worked at all! So that meant the electricity going round the circuit and the power to light up the bulbs were two different things...
They understood it in the end as the first bulb taking all the power and not sharing it, but the electricity still went all around the circuit (no intention to introduce current, voltage and resistance at this stage!).
When they were done writing, I asked them what they thought would happen if they made a circuit using two fans next to each other. Would they both work or only one or? F said only one fan would work... Which makes sense based on what they'd just seen with the bulbs!
Week 4:
After a quick discussion about the investigation we did last week, I asked them again what they thought would happen if we built the same circuit with two fans. They answered confidently that only one would work, of course! So we tested it...
Both fans came on at the same speed. 😂
Now the girls were confused! The fans must be sharing the power like they thought the bulbs would last week! Were they really? How could we test it? Take one fan away from the circuit... Yes, it came on at a faster speed than two fans together!
But why? Was there something wrong with our bulb experiment then? How could we test it? Maybe repeat it with different bulbs?
The sets I bought came with 6 bulbs all together, so we made a circuit with two cells and two bulbs and swapped them in and out of the bulb holders in turn to see what would happen... We saw three different results:
1) one bulb bright, one bulb off
2) one bulb bright, one bulb very dim
3) both bulbs dim
So what did this all mean? We decided to look at the bulbs closely and they could see some numbers and letters marked on the side of the metal - 3 bulbs had 2.5V, 2 bulbs had 3V and 1 bulb was unmarked! So what would happen if we only used bulbs of the same type in the circuit?
Of course, they behaved in the same way as the fans did and shared the power equally!
They wrote up this separate conclusion after their original one.
This was a good (unplanned and unexpected lol) lesson in checking all the variables in an experiment and a good reminder to me to swot up on the subject beforehand - I completely forgot to check the bulbs first and assumed they were all the same! So I researched why the bulbs behaved the way they did after the girls wrote their first conclusion... I didn't have the confidence at the time to challenge it. 😂😅 And it was a good lesson in the scientific method and how mistakes help us learn. 😆
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