Question Video: Identifying the Current Produced in a Slip Ring Generator | Nagwa Question Video: Identifying the Current Produced in a Slip Ring Generator | Nagwa

# Question Video: Identifying the Current Produced in a Slip Ring Generator Physics • Third Year of Secondary School

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What type of current does a slip ring generator produce?

03:53

### 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.

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