A company is making circuits. They need their circuits to have an
electric current that periodically reverses direction. What is the best choice for a
source of electric current? Is it (A) a chemical battery, (B) a
dynamo, or (C) either a dynamo or a chemical battery?
This question asks us for what can
supply an electric current that periodically changes direction. We’ve been asked to choose between
a chemical battery, a dynamo, or both as a power source. Let’s now think about which option
is the best answer.
We know that chemical batteries
only produce direct currents, since a battery produces a potential difference
between its terminals. The potential difference produces a
current in from one terminal to the opposite terminal. The only way to reverse the
direction of the current supplied to a circuit by a chemical battery is to reverse
the connections of the circuit to the battery terminals.
A dynamo is a machine containing a
coiled length of conducting wire that rotates in between the opposite poles of a
magnet. This induces an electric current in
the coil. For one complete rotation of the
coil of a dynamo, the current induced in the coil changes direction from its
original direction to the opposite direction to its original direction and then back
to the opposite direction. If the coil rotates uniformly, the
direction of the current changes periodically. It is easier to uniformly rotate a
coil than to repeatedly reverse the connections of a circuit to the terminals of a
So, our correct option is option
(B) a dynamo.