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.
