Video Transcript
The diagram provided shows an
electric circuit consisting of a cell and a bulb. Fill in the blank. In order to measure the potential
difference across the bulb, a voltmeter must be connected blank with the bulb. Is it (A) in parallel or (B) in
series?
This question asks if a voltmeter
in a circuit that measures the potential difference across a light bulb must be
connected in series with the bulb or in parallel with the bulb.
We know that a voltmeter measures
the potential difference between two points in a circuit. Remember that a potential
difference must be between two points. So in order to measure the
potential difference across the bulb, we’re going to need to choose two points at
which to connect the voltmeter that meet the following conditions. One, the points must be on opposite
sides of the bulb. Two, the points must have a path
that connects them on which there is a voltmeter and nothing else. And three, the points must also
have a second path that connects them on which there is the bulb and nothing
else.
It is extremely important to notice
that these conditions state there must be two different paths between the points on
either side of the bulb: one path has the bulb on it and the other path has the
voltmeter on it. If a bulb and a voltmeter are
connected in series, that means that they must be on the same path as each other,
and if the bulb and voltmeter are on the same path, they cannot each be on separate
paths.
A voltmeter connected in series
with a bulb cannot correctly measure the potential difference across the bulb. We reject option (B).
Any two paths that meet all the
conditions required are by definition parallel paths. When two components are on parallel
paths, these components are connected in parallel. We see then that the voltmeter must
be connected in parallel with the bulb. Option (A) is correct.
Filling in the blank, we have that
in order to measure the potential difference across the bulb, a voltmeter must be
connected in parallel with the bulb.
