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Course: Middle school physics - NGSS?>?Unit 2
Lesson 7: ElectromagnetismElectromagnetism
Moving electric charges create magnetic fields in the space around them. These magnetic fields can be used to generate magnetic forces. Oppositely, when magnetic fields are changed around charges, they can create moving electric charges, or electricity. Both of these phenomena are called electromagnetism, which is used in everyday items, from motors to medical scanners. Created by Khan Academy.
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Moving electric charges create magnetic fields in the space around them. We can use these magnetic fields to generate magnetic forces. Oppositely, when we change magnetic fields around charges we can create moving electric charges, or electricity. We call both of these phenomena electromagnetism. Incredibly useful, there are devices in everyday life that use electromagnets and electromagnetism.(34 votes) - How can a magnetic field have direction? Are there particles around a magnet that move in one direction or other?(19 votes)
- A magnetic field can have direction because the particles that surround it are either moving in the north or south direction(26 votes)
- What would happen if you put permanent magnet close to a electric magnet, would the electric current change directions.(15 votes)
- If you put a permanent magnet close to an electromagnet, it can indeed affect the direction of the electric current flowing through the electromagnet(9 votes)
- How do you know the direction of a magnetic field?(12 votes)
- The direction of the magnetic field around a coil can be determined by using the right-hand rule. Place your right hand around the coil with your thumb pointing in the direction of the current flow, your fingers will curl in the direction of the magnetic field.(13 votes)
- What if you charge a permanent magnet?(14 votes)
- charging a permanent magnet won't change its magnetic properties. It will remain a magnet and keep its magnetic field intact, regardless of any electric charge you give it.(7 votes)
- What determines the strength of a permanent magnet?(7 votes)
- A magnet's strength is affected by its size and the material it is made of. The environment also affects it (e.g. surrounding temperature).(11 votes)
- How does a spinning magnet cause an electric current? Not sure I fully understand the mechanics(7 votes)
- When a magnet spins near a wire, it creates a changing magnetic field. This changing field induces an electric current in the wire through electromagnetic induction.(2 votes)
- Does this mean that everything that has electricity in it is also a magnet? My toothbrush?(5 votes)
- Technically not, it would be magnetic from the metals, but not a magnet. Electromagnets are very specific on what metal they are wrapped around, and how many coils, so i do not think that a toothbrush would be considered a magnet.(5 votes)
- How do you change the direction of the electricity on a coil (thus, changing the direction of the magnetic field)? Do you just loop it in the other direction? (instead of looping it in a clockwise motion, you do it counter clockwise?)(5 votes)
- You just need to change the direction of the power source. For example, you can change a voltage with a ground and change the direction(4 votes)
- why can magnets get turned on and off.(3 votes)
Video transcript
- [Instructor] You know what a magnet is, but did you know that some
magnets can be turned on and off? One type of temporary magnet
is called an electromagnet. So what is electromagnetism? Well, the hint is in the name itself. Electro for electrical, and magnet for, well, magnet. Let's take a moment to
look at the definition of what an electromagnet is. Electromagnets are materials
that become magnets in the presence of electricity. But how does that even happen? Well, it turns out that electrically-charged
particles in motion actually have small
magnetic fields around them. So, if we run electricity through a wire, a magnetic field will be
created around the wire. Now, we can control the
strength of this magnetic field in a couple of ways. We can move more electric
charges through the wire at a faster rate, and we do this by increasing
the electrical current. The second way is to increase the density of the charged particles, and we can do this by
looping the wire into a coil. This gives us more charged particles with magnetic fields in a small space, strengthening the magnetic force. The other thing we can
control with electromagnets is the direction of the magnetic field, and we can do this by
changing the direction of the electricity. So if we go back to this
wire example from earlier and change the direction of the electricity
running through that wire, well, the magnetic fields
will also change direction. This makes electromagnets quite different from permanent magnets. So let's take a look at that and compare permanent
magnets to electromagnets. Electromagnets are typically made of loops of wire and a coil. The wire is typically
made of metal like copper and wrapped around pieces of metal like iron, nickel, or cobalt. This is different from a permanent magnet because permanent magnets
don't need this wire. Permanent magnets also have fixed poles. You can't change the north and
south poles on these magnets, but as we now know, for electromagnets, we can change these poles
by changing the direction of the electrical current. So, if we have an electromagnet
with a north and south pole that looks like this and a current flowing in this direction, well, we can change the poles and the direction of the current. Permanent magnets have a fixed strength, but we just talked about how we can change the
strength of electromagnets, so electromagnets have
adjustable strength. And finally, electromagnets
need a power source in order to generate
the electricity required to produce magnetic fields. Permanent magnets do
not need a power source, but this means that we can
also turn electromagnets on and off, which is pretty cool
when you think about it. On the other hand, permanent magnets are always on. Now, you might be thinking if electrical charge can affect magnetism, can magnetism affect electrical charge? Absolutely, let's look
at how we can do that. The only way to do this is by
changing the magnetic field around the charged particles. This can be done by moving magnets closer or further away from the particles or by spinning the magnets. In fact, spinning magnets is
how most of the electricity we use in cities and homes is generated. A turbine spins a magnet inside a coil to produce electricity, and since electromagnets
need a power source, this turbine is powered by wind. So you can see why electromagnetism is an incredibly important force, and this isn't the only
important application of it. We use electromagnets in all
sorts of other applications, from motors to speakers
and even medical scanners.