Magnetism

1. Magnetism • Electrons produce electric fields. • Moving electrons produce magnetic fields. • Electron spin produces the major portion of an objects magnetic field. • MOST elements have electrons with opposite spins, which cancel each other.

2. Magnetism • SOME elements, like iron and nickel, have an unbalanced number of electrons spinning in one direction and produce magnets. • A bar magnet produces a magnetic field with a north and south pole. • If you break it in half, the new magnets have north and south poles.

3. Magnetism

4. Magnetism

5. Magnetism • Magnetite is naturally magnetic and remains magnetic forever. • Most iron and ceramic magnets are placed in contact with a true magnet to be magnetized. They don’t last forever. • Dropping or heating them can weaken fields by realigning electrons.

6. Magnetism • Magnets may also be created by passing electric current through wires or coils of wires. These are called electromagnetics. • As current passes through a straight wire, a magnetic field is created in concentric circles surrounding the wire. • In a coil of wire, the field more closely resembles a doughnut shape.

7. Magnetism

8. Magnetism • If an electric charge moves through a magnetic field at a given velocity, it experiences a force that is perpendicular to the plane of the field and the velocity vector. • This requires a basic understanding of the cross product.

9. Magnetism

10. Magnetism • Calculate the magnitude and direction of the force created when an electron moves at a velocity of 5 x 1017 m/s to the right through a magnetic field of strength 5000 Tesla directed into the white board.

11. Electromagnetic induction • A magnet moved in and out of a coil of wire produces electricity. • This is called inducing a current, or induction. • The greater the number of coils, the higher the induced current. • When a magnet moves into a coil, it produce a different current than when it moves out of a coil. This is AC current.

12. Faraday’s law • Faraday’s law states that the induced voltage in a coil is proportional to the product of the number of loops, the cross sectional area of the loops, and the rate at which the magnetic field changes within those loops.

13. Electric motors • Electric motors use electrical energy to create magnetic fields which allow the motor to turn. • Motors use electricity to create motion. Generators work in the opposite direction: they turn mechanical energy into electricity. • A generator uses an energy source (windmill, hydroelectric plant, steam turbine, etc) to turn a wire loop in a magnetic field which in turn produces electricity.

14. Electric motors

15. Electric generators

16. Electric generators

17. Transformers • Transformers are used to increase or decrease the voltage. • For example, at the power generating plant, a step-up transformer is used to increase or step up the voltage for transmission down the power lines.

18. Transformers V1/V2 = n1/n2 is used to calculate the number of coils required on each side to step up or down a current.

19. Transformers • Calculate the number of coils on the secondary side needed to step 14,400 volts down to 120 volts if there are 5000 coils on the primary side. • Calculate the voltage produced on the secondary side if 200 volts are provided to the primary side, which has 1500 coils and a secondary coil count of 14500.

20. Transformers