Video Transcript
The following diagram shows an
electric circuit in two different arrangements. Which of the following statements
most correctly describes what the ammeter reads in Arrangement 1? (A) The ammeter reads zero. (B) The ammeter reads the current
in the circuit. (C) The ammeter reads half the
current in the circuit. Or (D) the ammeter reads twice the
current in the circuit.
To begin, let’s clear some room on
screen and recall that an ammeter measures the electric current at a point in a
circuit. Here, the circuit we’re concerned
with is Arrangement 1. So let’s take a closer look at its
circuit diagram. We see a cell, which provides a
potential difference across the circuit, a bulb, and an ammeter connected in
series.
We know that this is a series
connection because there’s only one path for charge to flow through. This is a good thing, since we know
that in order to correctly measure the current through a component in the circuit,
an ammeter must be connected in series with that component. So we can imagine this ammeter to
be measuring the current through the bulb.
This question is asking us what the
ammeter should read then. Well, the ammeter should not read
zero because there should be current present in the circuit. The cell provides a potential
difference. And in order for this bulb to even
work, there must be charge passing through it. So let’s eliminate option (A).
Options (C) and (D) suggest that
the ammeter has a nonzero reading but that the reading does not correspond to the
total current in the circuit. We know this isn’t right. There’s only one path for charge to
flow through the entire circuit. So the current at the point where
the ammeter is placed must be the total current, not half or twice the total
current. Thus, we know that (C) and (D) are
incorrect.
Answer choice (B) is correct. Since Arrangement 1 shows the
proper way to connect an ammeter to measure the current in the circuit, we know that
the ammeter simply reads the current in the circuit.
