Chapter 17 Magnetism

Magnetic? magnetism – the properties and interactions between magnets based on the alignment of particles in a substance magnetic – the ability of an object to make forces on magnets and other magnetic objects three types: permanent magnet temporary magnet electromagnet

What is Magnetism? The earliest magnets were found naturally in the mineral magnetite which is abundant the rock-type lodestone. These magnets were used by the ancient peoples as compasses to guide sailing vessels.

Permanent Magnets material that keeps its magnetic properties ex: your normal understanding of a magnet – fridge magnets, bar magnets…etc.

Temporary Magnets material which acts like a permanent magnet when inside of a strong magnetic field but lose their magnetism outside of it paperclips, nails, other soft iron items…etc. used in motors

Motors device which changes electrical energy into mechanical energy we use permanent magnets and electromagnets to make electric motors and generators generators turn mechanical energy to electrical energy these work by changing the direction of the electric current

Electromagnets helix of wire tightly wrapped around an iron core – acts like a magnet when current is applied to it strength of the magnet varies with the current [more current, more magnetized]

Magnetism …[review] is based on the alignment of particles in a substance. all atoms have moving electrical charges [electrons] these moving electrons cause a magnetic field this causes the Faraday Effect Faraday Effect Clip

Magnets The magnetic field lines around horseshoe and disk magnets are closest together and strongest at the magnet’s poles. Unlike poles of magnets attract each other Like poles of magnets repel.

Magnetic Fields are stronger nearer to the top of magnet create North [pull north] & South [pull south] poles a pole is where the force of the magnet is the strongest each pole is attracted to the other [hence the swirls of field from N to S or from S to N]

Magnets The earth is like a giant magnet! The nickel iron core of the earth gives the earth a magnetic field much like a bar magnet.

Magnetism atoms in an object behave like tiny magnets In an area of an object where all of the particles have a similar magnetic field is called a domain the particles of most objects are not aligned

Magnetism …[the particles of most object are not aligned] aligning particles will cause an overall magnetic field the force of a magnet depends on the alignment of its particles

Another magnet can cause the alignment of an object’s electrons Magnetism Another magnet can cause the alignment of an object’s electrons

Magnetic Fields

What are magnetic domains? Magnetic substances like iron, cobalt, and nickel are composed of small areas where the groups of atoms are aligned like the poles of a magnet. These regions are called domains. All of the domains of a magnetic substance tend to align themselves in the same direction when placed in a magnetic field. These domains are typically composed of billions of atoms.

Electricity and Magnetism – how are they related? When an electric current passes through a wire a magnetic field is formed. The direction of the current depends on the directions of the current in the wire, to a position of lower potential energy.

What is a galvanometer? A galvanometer is an electromagnet that interacts with a permanent magnet. The stronger the electric current passing through the electromagnet, the more it interacts with the permanent magnet. The greater the current passing through the wires, the stronger the galvanometer interacts with the permanent magnet.

We have seen how electricity can produce a magnetic field, but a magnetic field can also produce electricity! How? What is electromagnetic induction? Moving a loop of wire through a magnetic field produces an electric current. This is electromagnetic induction. A generator- used to convert mechanical energy into electrical energy by electromagnetic induction.

What are electric motors? Simplest Electric Motor Clip

How does an electric motor work? Go to the next slide 

Simple as that!!

Direct current versus alternating current – AC vs DC : What’s the difference? Direct current is electrical current which comes from a battery which supplies a constant flow of electricity in one direction. Alternating current is electrical current which comes from a generator. As the electromagnet is rotated in the permanent magnet the direction of the current alternates once for every revolution. Go to this website and click the button for DC then for AC to visually see the difference between the two. You can see that the DC source is a battery – current flows in one direction. The AC source is the generator and the current alternates once for each revolution.