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Question Video: Determining the Number of Voltmeters in a Circuit Science

The diagram shows an electric circuit. How many voltmeters are there in the circuit?


Video Transcript

The diagram shows an electric circuit. How many voltmeters are there in the circuit?

In this question, we are given a diagram of an electric circuit with multiple different components. Remember that each symbol on a circuit diagram represents a specific component. So anyone looking at a diagram can quickly tell what is in it.

Let’s briefly label each of these so we can determine how many voltmeters are present. This is the symbol for a power cell, with the small line representing the negative side and the large line, the positive side. The symbol to the left of this cell is a switch, indicated by these two circles and a line that can be used to cause a break in the circuit. All of the other symbols besides these two are circles but with different markings inside them. The circles with Xs indicate light bulbs, the circle with A indicates an ammeter, and the circles with V indicate voltmeters.

So, all components accounted for, we can clearly see that there are two voltmeters here. But oftentimes it is not enough to merely have voltmeters or any component for that matter present in a circuit. We should also ensure that they are set up correctly. When we are attaching a voltmeter to a circuit, it is important that we connect it in parallel with the circuit on either ends of the component we wish to measure the potential difference across. We do this by taking the ends of the voltmeter and attaching them at two separate points along the wire. For this specific circuit, such a setup allows us to measure the potential difference across this light bulb and this one.

Since both of these voltmeters are connected in parallel with the circuit, we can say that they are set up correctly. Compare these voltmeter connections to the ammeter. We see that it is attached in series with the circuit, rather than in parallel, because it has to measure the current in the wire, rather than the potential difference across a specific component. Therefore, we can say that it is also connected correctly. But we don’t need to know how many ammeters there are, just voltmeters. As we’ve already determined, the number of voltmeters in this circuit, the circles with the letter V inside them, is just two.

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