Video Transcript
Each of the following diagrams
shows an electric circuit. Which one shows how the ammeter
must be connected to the circuit in order to measure the current through the
bulb?
Before answering the question,
let’s review some facts about ammeters and currents in electric circuits.
We know that an ammeter is used to
measure the electric current in a wire. For an ammeter to measure the
current through a component, the ammeter must be connected in series with the
component and not in parallel. Remember, connecting components in
series means that they are on the same path through the circuit, while connecting
the component in parallel means that they are on separate paths.
Let’s look at a few more examples
of components connected in parallel. Each of these may look a little bit
different, but they are all examples of ammeters connected in parallel with one or
more bulbs. We know that they are connected in
parallel because if we draw a path from one terminal of the cell to the other
terminal of the cell, the path can’t go through both an ammeter and a bulb.
We can draw some of the paths that
the current could take onto the circuit diagrams. All of the pink paths pass through
a bulb, and all of the green paths pass through an ammeter. But none of the paths pass through
both a bulb and an ammeter. So, all of these ammeters are
connected in parallel with the bulbs. This is not how ammeters should be
connected.
Out of the options we’ve been
given, option (A) is the only diagram that shows an ammeter connected to a bulb in
series. The only path that the current can
take through the circuit passes through both the ammeter and the bulb. This is the correct way to connect
an ammeter.
Now that we know that ammeters
should always be connected in series, we can see that option (A) is the only diagram
that shows the correct way to connect an ammeter to this circuit.
