Magnets and Magnetic Fields& 4 Right hand rules

Chapter 24

What is magnetism?Magnetism is the properties and interactions of magnetsThe 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.

Magnets:Ferromagnetic- materials that can be

magnetizedExamples: Iron, Copper, Nickel, Cobalt, the alloy

Lodestone

2 typesSoft: Materials that can be magnetized but don’t

stay magnetized very longHard: Materials that take a lot/long time to

become magnetized, but stay magnetized. These are called Permanent Magnets

Electromagnets

How are Magnets Used Today?

Magnets have two ends or poles, called north and south poles. At the poles of a magnet, the magnetic field lines are closer together.

Unlike poles of magnets attract each other and like poles of magnets repel.

The Earth has 4 Poles!!?The magnetic field of the earth comes from the rotation of the the earth and from the convection of the hot molten core.

The Earth’s magnetic field extends far into space. It is called the “magnetosphere.”

When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called…

The Aurora Borealis in the Northern HemisphereThe Aurora Borealis in the Northern Hemisphere

And the Aurora Australis in the Southern HemisphereAnd the Aurora Australis in the Southern Hemisphere

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.

Things that work because of magnetic domains….

ElectromagnetismMagnetic field from a single wire:

1st Right-hand rule: Thumb in the direction of the current = Fingers CURL in direction of magnetic field

What is an electromagnet?When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.

ElectromagnetismMagnetic field from a coil (solenoid):

2nd Right-hand rule: Fingers CURL in the direction of the current = Thumb in the direction of magnetic field

Forces Caused by Magnetic Field

Direction of Force on wire from Magnetic Field3rd Right-hand Rule: Thumb in the direction of

current = Palm in the direction of Force

Equation: F=ILB – The force on a current-carrying wire in a magnetic field is equal to the product of the current, the length of the wire, and the magnetic field strength

Jumping Wire Demonstration

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 is interacts with the permanent magnet.

The greater the current passing through the wires, the stronger the galvanometer interacts with the permanent magnet.

Galvanometers are used as gauges in cars and many other applications.

What are electric motors?An electric motor is a device which changes electrical energy into mechanical energy.

Go to the next slide

How does an electric motor work?

Simple as that!!

Forces Caused by Magnetic Field

Direction of Force on charge from Magnetic Field

Equation: F=qvB – The force on a particle moving in a magnetic field is equal to the charge of the particle, its velocity and the field strength.

Cathode Ray Tube

TV Demonstration