Problem with Q12 of ABC v.5 Basic Circuit Troubleshooting

Thread Starter


Joined Dec 7, 2012
I'm stuck on Q12 on this page. In the answer, it says the listed measurement results tell you that the bulb has good continuity. But if the break is between points D and E, wouldn't a 0V result between E and J be nondeterminative about the bulb?


Joined Jul 24, 2018
Technically, you can determine the bulb is continuous from this. The reason is because you are able to take a measurement of voltage across the break before the bulb. That means point E is at the circuit ground, and isn't floating. In order to be at ground, there has to be a continuous path between E and J as well. If the bulb were broken, then E wouldn't be at the ground voltage (not connected to the other terminal of the battery), but at some random potential, and you'd read a zero volt potential on the voltmeter across D and E.

If you need an intuitive example, think about testing a battery to see if it's charged: if you connect just one lead to the battery, you'll not read 1.5V or 9V, but the meter will say 0, because there's no reference point for the other probe. The same reason is why there must be a continuous path through the light.

Hopefully that answers your question and doesn't muddy the waters too much!


Joined Mar 30, 2015
Did you post in Homework Help because you want us to give you hints vs just describing our thought process?


Joined May 15, 2009
Think through your circuit again and if you like indicate where voltages are measured.
Remember Ohm's law about voltages, currents and resistance. In this case I think we can assume that the resistance of a non-illuminated but functional bulb is very low and the same for the wires. If the bulb resistance was high what would that tell you about the voltages you would expect?