Magnets Magnetism: property of some materials that allows them to give off an attractive or repulsive force. Magnet: a material that gives off an external magnetic field, making it possible to apply a force over a distance. I like to pass around different magnets (horseshoe, bar, etc.) so students can feel the magnetic field and the force as they slowly move the magnets towards and away from each other. They may also notice that some orientations do not create this attractive force, which can lead into talking about poles on the next slide.

Magnetic Force All magnetic objects have a force between them. Can be attractive or repulsive. Think about some of the other forces we’ve talked about this year. Is this similar or different from them? The attractive force decreases the farther apart the magnets are. Force is strongest at the magnetic poles North and South For the embedded question I like to discuss electrical force and gravitational force. How magnetic force is similar to electrical in a lot of ways, particularly in how they can both be attractive or repulsive, whereas gravitational force is only attractive. However magnetic and gravitational are similar in that the farther apart the objects, the less the force.

Magnetic Force Magnetic poles cannot be isolated.

Note: Field direction is always North to South Magnetic Field Magnetic Field: external force given off by a magnet; strongest at the poles. Allows magnets to apply a force over a distance. Strength of the magnetic field is based on the material the magnet is made of. Note: Field direction is always North to South

Magnetic Field Magnetic fields result in a force that is either attractive or repulsive. Opposites attract Like repel

Earth’s Magnetic Field Earth’s core is made of various metals, that are oriented to act like a giant bar magnet in Earth. This is why we have North and South poles! How a compass works: Earth’s bar magnet actually has the South pole of the magnet as our geographic north pole, and vice versa. Thus when using a compass, the needle points North when it is attracted to Earth’s magnetic south pole.

Magnetic Domains All atoms have the potential to be magnetic due to the magnetic properties of electrons. In magnetic elements, each atom behaves like a magnet with north and south poles, all aligned to make a magnetic field. In nonmagnetic elements, these magnetic domains are not always aligned, thus resulting in no apparent magnetism.

Ferromagnetism Ferromagnetism: phenomenon where objects placed in a strong magnetic field become magnetized due to the poles within their atoms aligning (all e- in same direction). This is how nonmagnetic elements like iron, cobalt or nickel can become attracted to magnets. Demo: Your whiteboard is most likely magnetic. If you try to hold a paper clip up to the whiteboard, it will not “stick” to it. However, if you have a strong enough magnet (like a horseshoe magnet) they can pick up the paper clips, due to the magnetic field of the horseshoe magnet being strong enough to align the atoms of the paper clip to make them attracted to the magnet.

Electricity and Magnetism Moving electric charge (current) can produce a magnetic field. The magnetic field generates in counterclockwise circles around the direction of the moving e-. The stronger the current, the stronger the magnetic field that can be produced.

Electromagnets Temporary magnets can be made using the presence of strong magnetic fields or current. Electromagnet: temporary magnet made by placing a piece of iron inside a current carrying coil of wire. Switch open No current Nail not magnetic Switch closed Current flows Nail is magnetic

Electromagnets The more loops of wire, the stronger the magnetic field. The stronger the current, the stronger the magnetic field.

Electromagnets In the real world Electric Motor: device that uses an electromagnet to convert electrical energy into mechanical energy. Generator: device that uses an electromagnet to convert mechanical energy into electrical energy.