How to Turn on a Light Bulb With a Battery

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When using a battery to turn on the light bulb, it's highly important that the battery and the light bulb match in terms of power requirements. Find out how to use eight 1.5 volt batteries to power a 12 volt light bulb with help from a science teacher in this free video on electricity and physics.

Part of the Video Series: Physics & Electromagnetism
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Video Transcript

Hi, I'm Steve Jones. I'm going to tell you how to turn on a light bulb with a battery. Now this is a little more difficult than you might think because the light bulb and the battery have to match. This is the important thing. All you have to change the battery to suit the light bulb. Now if I have a light bulb, on it it will say something like oh 1 watt, 12 volts. What that means is the power it uses is 1 watt and the voltage it needs is 12 volts and it'll use 1 watt at 12 volts. If I reduce the voltage, I'm sorry, it won't work very well. If I use a 1 volt or 1 and a half volt supply, this will be very dim. I won't get much current, that's the problem. If I have a 1.5 volt cell like this, well this will not drive that. I can put the two together and what will happen is this will glow maybe a little bit but it won't act as a light bulb. So you would say ah, well look, what if I took 8 of these and attached it to that? Yes, that's OK. If I take 8 of these, right? And I attach them so that I've got them all in series, one after the other, I'll end up with a battery, this is what a battery is and that battery would be 8 times 1.5 volts which is 12 volts and yes, it should drive this bulb. Providing this can supply enough current because as well as getting the right voltage, you have to be able to get enough current. Now I can get 12 volts from my car starter motor but if I use this type of thing for my car starter motor, yes I can get 12 volts but the problem is as soon as I try and actually the starter motor, nothing will happen because this kind of cell, this kind of battery can't supply 200 amps. In fact it's going to be a maximum of half an amp and this is because the current depends on how much resistance this has. So how much resistance this is called the filament, how much resistance the filament has. And if the filament has a low resistance, you're going to get a high current. Now so what do I say? The answer is if you are using this kind of cell, don't expect to get more than half an amp. If this for example is 12 volts and 1 watt, in fact this will work quite happily from these because the current alright? The current is going to be a 12th of an amp, less than a 10th of an amp, a very small current, that's fine but it won't work if you use a car, if you use a car headlight and they might be something like 48 watts in which case you would get 4 amps and I'm sorry, this won't manage. So turning on a light bulb with a battery is more than just matching the voltages, you have to look at the currents too. If the power is big, even if the voltage is small, if the power is big, then you're going to have a big current and that will mean that you need a more powerful battery. So there you are, turning on the light bulb with a battery in simplified form.


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