Electric and Magnetic Forces Chapter 3 Electric and Magnetic Forces

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

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

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?

+ - + + + - + + + 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 + - + + + - + + +

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

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

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.

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

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.

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?

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.

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

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

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?

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

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?

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

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)

Concept Check What did we learn so far?

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

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

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

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