A student joins an ammeter in parallel with a bulb, instead of in series.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student joins an ammeter in parallel with a bulb, instead of in series. What happens to the bulb, and to the ammeter? Why is an ammeter made with a very small resistance?
Need a reminder? The key ideaShow
The potential difference is the work done per coulomb: , in volts (). So . An ammeter goes in series; a voltmeter goes in parallel.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The current's choice. The ammeter offers a path of almost no resistance beside the bulb, so nearly all the current goes through the ammeter.
Step 2. The result. The bulb goes out, a large current flows, and the ammeter can be damaged.
Step 3. Why small. In its proper place, in series, the ammeter's tiny resistance hardly changes the current it measures.
Answer: the bulb is shorted out and the ammeter may burn; an ammeter must go in series.
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