1. Unit 7: Electricity & magnetism
{17.1 – Electric Charge & Force
{18.1 – Magnets & Magnetic Fields

2. {17.1 - Electric Charge & force
Electric Charge – an electrical property of matter that creates electric and magnetic interactions
“Conservation of charge”: Electric charge is never created or destroyed.

3. {17.1 - Electric Charge & force
Causes of electric charge: an imbalance in the number of protons and electrons in an atom, molecule or other object
Types of charges
Negative charge – more electrons than protons
Positive charge – more protons than electrons
No charge – equal amount of protons and electrons

4. Transfer of electric charge
What causes an imbalance of charge?
When different materials are rubbed together, electrons can be transferred from one material to the other.
Direction in which the electrons are transferred depends on the materials
Triboelectric Series - common materials are listed according how well they create static electricity when rubbed with another material, as well as what charge the material will possess

5. Transfer of electric charge
“More positive” - materials that gain a positive (+) electrical charges (tend to give up electrons)
“Neutral” - do not tend to readily attract or give up electrons
“More Negative” - materials that gain a negative (−) electrical charges (tend to attract electrons)

6. Transfer of electric charge
Electrical conductors allow charges to move freely
e.g., copper in cords
Electrical insulators do not allow charges to move freely
e.g., plastic in cords

7. How objects get charged
(1) Charged by friction - one material gains electrons and becomes negatively charged while the other loses electrons and becomes positively charged
e.g., static electricity-pulling clothes out of the dryer and finding that they are stuck together

8. How objects get charged
(2) Charged by contact – objects charged by touching a charged object to a neutral object
e.g., touching a charged rod to a neutral doorknob

9. How objects get charged
(3) Charge by induction– redistribution of charge within a neutral object brought about by bringing a charged object close (but not touching)
Overall charge of the object is still zero, but opposite sides will have an induced charge
e.g., bringing a charged rod to a neutral doorknob

10. How OBJECTS GET CHARGED
How charged objects behave:
Opposite charges attract
Like charges repel.

11. Electric discharge
Static electricity (electrons that move from one object to another and cause the buildup of charges at rest) eventually leave the object
When the object loses its charge, it becomes neutral again
electric discharge-the loss of static electricity as electric charge moves off an object
This can be slow and quiet or very rapid and accompanied by a shock, a spark of light, or a crackle of noise (e.g., lightning)

12. Electric discharge

13. Electric Force
Electric Force – the force of attraction or repulsion on a charged particle that is due to an electric field
electric field – the space around a charged object in which another charged object experiences an electric force
Electric force depends on
(1) charge
(2) distance

14. Electric Force
Positively Charged Particle

15. Electric Force
Negatively Charged Particle

16. Electric Force
Like Charged Particles

17. Electric Force
Oppositely Charged Particles

18. {18.1 - Magnets & magnetic fields
Magnet: Piece of material with property of attracting iron (or steel)
Produce magnetic fields and attract metals like iron, nickel, and cobalt.
Magnetism: The force of attraction between magnetic materials is due to the arrangement of electrons.

19. Copy this diagram into your notes.
Lines of force
Lines of Force
Magnetic field's lines of force exit the magnet from its north pole and enter its south pole.
Shows area over which a magnetic force is exerted
Strongest force at poles
Copy this diagram into your notes.

20. Magnets & magnetic fields
Magnetic Force
Like poles repel
Opposite poles attract
Copy these diagrams into your notes.

21. Magnets & magnetic fields
Types of Magnets
Ferromagnetism: Materials that can be magnetized (iron, cobalt, nickel)
Permanent or hard magnets: create their own magnetic field all the time.
Temporary or soft magnets: produce magnetic fields while in the presence of a magnetic field and for a short while after exiting the field.
Electromagnets: produce magnetic fields only when electricity travels through their wire coils.

22. Magnets & magnetic fields
Magnetic Domains
Magnetic Domains: Groups of atoms where the magnetic poles of all the atoms are aligned in the same direction.
Copy this diagram into your notes.

23. Magnets & magnetic fields
Electromagnetism
An electric current flowing through a wire creates a magnetic field whose direction depends on the direction of the current.
Right Hand Rule
Solenoid: A long coil of wire with many loops.
More loops = stronger magnet

24. Magnets & magnetic fields
Earth’s Magnetic Field
Geographic north pole is actually magnetic south pole.

25. Magnets & magnetic fields
Compass
A compass needle is a magnet!
N pole of magnet always points N except when its near a strong magnet.
North pole of compass points to south pole of magnet.
Copy this diagram into your notes.