1. Electric and Magnetic Forces
Chapter 3
Electric and Magnetic Forces

2. Forces acting over a distance
In last chapter we discussed forces mostly in direct contact such as an applied force ( push or pull ) Ex. Person pulling a rope
The forces that act over a distance are going to be exerted over what we call a "field". These forces are called field forces.
Definition of field (from Physics): region of space characterized by a physical property, such as gravitational or electromagnetic force

3. Lets try this question….1
Which of the following is NOT an 
example of a force being exerted through a field?
[This object is a pull 
tab]
Answer B A
Gravity pulling on a falling apple B
A man pushing a car C
A magnet attracting a steel ball D
An electrically charged balloon pushing on another balloon from across the room
Answer - B

4. What is electric charge?
Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter
2 types : Positive and Negative
Have you ever felt an electric shock? The reason you get a shock is because of moving electric charges. Moving electric charges also create lightning bolts and the electric current that flows through cables and wires.
Question – What do you know about the dangers of lightning during a storm?

5. + - + + + - + + + Positive Charge
Objects that are positively charged are out of balance, 
meaning they have more protons than electrons.
Think back to the atom with protons and electrons, the electrons will move through the objects

6. + - + + - - - - - Negative Charge
Objects that are negatively charged 
are out of balance, 
meaning they have more electrons than protons.

7. Opposites Attract Same Charges Repel Opposite Charges Attract
The force of attraction or repulsion between charged particles is called electric force.
Like gravity, electric forces can act on objects that do not touch

8. How strong is the force?
The strength of electric force depends on the amount of electric charge and the distance between the charged particles.
The larger the charge or the closer together the charges are, the greater is the electric force.

9. Electric forces in every day life
Has this ever happened to you? This is electrostatic force
Other examples: -Batteries to charge cell phones -Lightning in a storm -Wattage to light a lightbulb

10. Electric Fields
Electric force is exerted over a distance, so charged particles do not have to be in contact in order to exert force over each other
An electric field is a space around a charged particle where the particle exerts electric force on other particles.

11. Field lines between like charges
Both diagrams help us visualize repulsive forces.
Do you see how the lines look

like they are pushing apart at 

their closest points?

12. Field Lines between unlike charges
This diagram indicates electrostatic attraction.
The field lines exit the positive charge
and enter the negative charge.
Unlike the field lines between like

charges, these lines look like 

they are pulling together.

13. Magnetism
Magnetism- The force of attraction or repulsion of magnetic of magnetic materials.
A magnet is an object that attracts certain materials such as iron Question* – Look at the bar magnet photo, describe what is happening

14. Magnetic Poles Every magnet has 2 poles - North and South It's similar to the charge being either positive or negative *Magnets are strongest at the poles

15. Magnetic Poles North and South poles attract
Magnetic force- a force produced when magnetic poles interact.
Question – Why are these paper clips attracted to this magnet? How?

16. Magnetic Field
Magnetic field- the region around a magnet where the magnetic force is exerted.
Example of Magnetic Field Iron Filings around a magnet to show field

17. Compare the spacing of the field lines at A vs. B
As we move away from a magnetic pole, What happens to the strength of the magnetic field? A B
Compare the spacing of the field lines at A vs. B
What do you notice?

18. What do you notice about the field lines of 2 bar magnets?

19. Did you know the Earth has a giant magnetic field
Did you know the Earth has a giant magnetic field? It has a magnetic field to protect against solar flares from the sun The field is a reason we have Auroras ( Northern and Southern Lights)

20. Concept Check
What did we learn so far?

21. 23
As the amount of charge increases, 
the force between the charges __________.
[This object is a pull tab]
Answer C A
decreases B
stay the same C
increases
Answer - C

22. Answer - True 21 An electron and a proton are attracted to each other.
[This object is a pull tab]
Answer
True
True
False
Answer - True

23. Answer - B 35 Like ( Similar) such as South and South magnetic poles:
attract
[This object is a pull tab]
Answer B B
repel C
don't interact
Answer - B

24. 40
As distance is increased away from a 
magnetic field source, the magnetic 
field intensity will ___________.
[This object is a pull tab]
Answer B A
Increase B
Decrease C
Stay the same
Answer - B