Video Transcript
What type of current does a slip
ring generator produce?
Before we answer this question,
let’s remind ourselves about slip ring generators and how they work. Once we know this, we should be
able to work out everything we need to know about the current to answer this
question. Recall that a generator uses
electromagnetic induction to produce electricity. In a generator, a coil of wire is
placed in between a north and south magnetic pole. In order to generate a current,
mechanical forces are applied to the coil of wire to make it rotate. When the coil rotates, a current is
produced in the coil.
Usually, we use generators to
produce a current in some external circuit and not just in the coil. To do this, we need to connect the
coil to the external circuit so that the current produced also passes through the
circuit that we want to power. However, because the coil is
rotating, we can’t just use wires to connect the circuit. The wires would get tangled up and
twisted as the coil rotates. Instead, different methods are used
to connect the coil to the external circuit. One such method is to use slip
rings.
Slip rings are simply rings made
from a material that conducts electricity. A generator uses two slip
rings. One ring is connected to each end
of the coil of wire. As the coil of wire rotates, so do
the slip rings. The slip rings are then connected
to the external circuit using brushes. The brushes are also made of a
material that conducts electricity and are placed in contact with the slip
rings. As the slip rings rotate, they rub
against the brushes, which allows the current produced in the coil to reach the
external circuit. Note that the slip rings don’t
change the current in any way. The current that reaches the
external circuit is exactly the same as the current produced in the coil.
Now that we know how a slip ring
generator works, we can work out what kind of current it produces. Let’s start by recalling some
information about electromagnetic induction. Electromagnetic induction occurs
when the magnetic field passing through a loop of wire changes. This causes a potential difference
to be induced across the loop, which produces a current. So, how does this process work in
generators? To make this easier to think about,
let’s look at our generator from a slightly different angle.
Here, we’re looking along the axis
of rotation of the coil. Even though the coil is still a
rectangular loop, it appears to be a straight line from this perspective. The coil is rotating in this
direction. We can also add the magnetic field
lines onto our diagram like this. At first, the coil is oriented
parallel to the magnetic field. We can see that no magnetic field
lines are passing through the loop.
Now imagine the loop sometime
later, when it is perpendicular to the magnetic field. We can see that, now, several
magnetic field lines are passing through the loop. So, as the coil rotates, the
magnetic field passing through it changes. This causes a potential difference
to be induced across the coil, which produces a current in the coil. The direction of this current
changes every half turn of the coil. If we were to draw a graph showing
how the current produced in the coil varies with time, we would find it looks
something like this. This graph shows the change in
current for one full rotation of the coil.
It’s important to notice that in
this region, the current in the coil has a positive value, while in this region, the
current in the coil has a negative value. This tells us that the current in
the coil changes direction as the coil rotates. A current that changes direction in
this way is called alternating current.
So, we have worked out that the
current in the coil is an alternating current. However, that isn’t what this
question is asking us. We actually need to find the type
of current that the slip ring generator produces in the external circuit. Luckily, this part is very
simple. The slip rings transfer the current
from the coil to the external circuit, without changing the current in any way. So, the current produced by the
generator is the same as the current in the coil, an alternating current. So, this is our final answer to
this question: a slip ring generator produces an alternating current.
