1. Magnetism and Electromagnets
After previously learning to measure electricity, now we will learn what exactly electricity is on the atomic level.

2. Permanent Magnet
A permanent magnet is a material that keeps its magnetic properties, even when it is not close to other magnets.

3. Poles
All magnets have two opposite magnetic poles.

4. Attraction

5. Magnetic Fields
Magnetic field lines always point away from a magnet’s north pole and toward its south pole.

6. What does the direction of magnetic field lines tell you?
Magnetic field lines point in the direction of the force from the north pole.

7. Magnetic Declination
The difference between the direction a compass points and the direction of true north.

8. Gauss The unit to measure the strength of a magnetic field.
Earth’s magnetic field averages about 0.5 gauss at the surface.

9. Electromagnets
Magnets created by electric current flowing in wires.

10. Earth’s Magnetism
Huge electric currents flowing in the molten iron produce the Earth’s magnetic field (like an electromagnet!).

11. Right Hand Rule

13. Electromagnet Poles
“right-hand-rule”

14. Advantages
You can switch an electromagnet on and off by switching the current on and off.
You can switch an electromagnet’s north and south poles by reversing the direction of the current in the coil.
The strength can be changed by changing the amount of current in the coil.
Can be much stronger than permanent magnets when using large currents.

16. Use right-hand-rule to describe the north and south pole.

17. Electromagnetic Induction

18. Magnetism in a Wire Created by moving charges
Field lines are concentric circles with the wire at the center
Concentric: circles of different sizes

19. Magnetic Field Strength
Directly proportional to the current, doubling the current doubles the strength of the magnetic field
Inversely proportional to the distance from the wire
Stronger as you move closer to the wire
Decreasing the distance to the wire by half doubles the strength of the field

20. Coil
A single wire can be looped into a coil, concentrating the magnetic field at the coil’s center.
Solenoid

22. Electric Motors
Convert electrical energy to mechanical energy

24. Electric Generators and Transformers
Electromagnetic Induction – the process of using a moving magnet to create electric current or voltage.

25. Magnet must be moving in order to produce current
A changing magnetic field is what creates current

26. Faraday’s Law of Induction
The voltage induced in a coil is proportional to the rate of change of the magnetic field through the coil.

27. Sub Day Questions and Answers

28. 2. What exists in the region around a wire that is carrying current and that exerts a force on another current-carrying wire?
A magnetic field.
3. Explain how the right-hand rule can help you determine the direction of the magnetic field lines around a current-carrying wire.
Wrapping the right hand around a current carrying wire with the thumb pointing in the direction of the current will cause the fingers to wrap in the direction of the magnetic field that surrounds the wire.
4. What effect does increasing the current in a wire have on the magnetic field?
The magnetic field becomes stronger as the current increases. Field strength is directly proportional to the current.

29. 5. What effect does reversing the direction of the current in a wire have on the magnetic field?
The direction of the magnetic field will be reversed if the current is reversed.
6. What happens to the magnetic field as you move farther away from a current-carrying wire?
The strength of the field surrounding a wire will decrease as the distance from the wire increases.
7. Why do we not use a single wire with a large current if we wish to create a strong magnetic field?
It is easier and safer to work with a small current.

30. 10. A motor turns _____ energy into _____ energy.
electrical, mechanical
11. Why is it necessary to use at least one electromagnet in a motor instead of only permanent magnets?
So that the polarity of the magnets can be more easily reverses at the proper time in the rotation of the motor.
12. What is the purpose of the commutator in a motor?
The commutator reverses the polarity of the electromagnets at the proper time in the sequence of rotation.
13. Why must the direction of the current in a motor’s electromagnets be
switched repeatedly?
The current must be continually reverses so the electromagnets will continually change polarity.

31. 15. What happens as you move a magnet toward a coil of wire in terms of
electricity?
If you move a magnet through a coil of wire it will induce a potential difference in the coil that will cause a current to flow if the coil is part of a circuit.
16. If you hold a magnet still near a coil of wire, will current or voltage be
induced? Explain your answer.
No. A magnet will only induce a voltage in a coil if the magnet is moving relative to the coil.
17. State Faraday’s law of induction in your own words.
The voltage induced across the ends of a coil is directly related to the speed with which a magnet must pass through a coil.