I connected a 1 ohm resistor to a 9V battery.. the resistor rating was 1/4W.. I know by common sense that the battery won’t deliver 9A.. the resistor didn’t burn.. when I did it theoretically I = V/R.. = 9A but practically this does not apply.. can you please explain..
You are correct with Ohm’s Law stating at 9V you will get 9A across your 1Ohm resistor, but this is in a perfect world. Because you are working with a battery and not a regulated power supply, the battery’s voltage is going to start at ~9V then quickly drop, resulting in significantly less power being dissapated. There is a really cool article by Richard Friedrich and Rogelio Ramirez from Friedrich Engineering that uses a series of tests to determine the output capability of a PP3 9V battery. From their tests, it appears that your battery might be either a bit low or with a chemistry that does not allow for high current loads.
My advice to you would be to perform the same experiment with the same battery, but this time have a multimeter attached to the + and – on the battery to monitor voltage. Record your voltage drop every 5s or so, then repeat the experiment using the multimeter to measure the current flowing through the circuit. You can then analyze your data and determine the cause of your resistor not igniting 🙂
Good luck with your experiment, but MAKE SURE YOU ARE CONDUCTING YOURSELF IN A SAFE MANNER! Wear safety glasses, work in a ventilated area, and don’t touch hot things…because they are hot! We do not condone unsafe activities, and hold no responsibility for injury of any kind if any happens to occur.
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“Ask an Educator” questions are answered by Adam Kemp, a high school teacher who has been teaching courses in Energy Systems, Systems Engineering, Robotics and Prototyping since 2005.