1. Electromagnetic Force Some of this is a review from when we covered electricity and circuits. Yay!

2. What causes charge? Charge, measured in Coulombs (C), is caused by ions (elements that have either lost or gained electrons). The more ions there are, the bigger the charge is.

3. Electricity Electricity is caused by the movement of electrons from these ions. Atoms prefer to be neutral, so electrons will frequently move from areas of high concentration to areas of low concentration (to spread out)

4. Current Sometimes the electrons/charges move faster than other times. Charge that moves faster is said to have a greater current (I). Current is the rate at which charges move. It is measured in amperes 1 amp is 1 Coulomb per second – 1 amp = 1 C/s

5. Voltage Not all charges have the same amount of energy. The average amount of energy a group of charges carry is called its voltage (V). Voltage acts as the “pressure” of a circuit. Voltage is measured in volts. 1 Volt is 1 Joule per Coulomb – 1 V = 1 J/C – Remember: Joules are the unit of energy!

6. Static Electricity When there is an excess of charge (positive or negative) built up in an object, it is said to have static electricity – Static means not moving; electricity is the movement of electrons…..oxymoron! The greater the charge, the more likely it will be to jump out to balance itself. When two objects of different charges get close enough, the electrons jump from the negatively charged object to the positively charged one.

7. Effects on the Human Body Since our brain communicates through our nervous system to the other cells by means of electricity, an electric shock can do quite a number on you. It can cause pain, spasms, and cell death, all normally caused by instructions the brain gives via electricity.

8. Other Effects Because electricity is a type of energy, and a transfer (e.g., electric  electric) or transformation (e.g., electric  radiant) of energy always results in a “loss” of initial energy as thermal energy (heat), electric shocks tend to make the affected areas quite hot. If too much electrical energy jumps to the same area, it could even start a fire.

9. Lightning Lightning is when a great positive or negative charge gathers in a relatively small area in the sky. Sometimes another nearby cloud has the opposite charge and the electrons even out between the two, creating a cloud-to-cloud lightning strike. Other times there is nothing closer than the earth (universal donor/acceptor of electrons), creating a cloud-to-ground/ground-to-cloud lightning strike.

10. Effects of Lightning Often, a lightning strike that hits somewhere will start a fire, due to the amount of energy lost as thermal energy in the transfer being greater than the ground/grass/house’s heat of combustion. Even more often, it will scorch the surrounding area. If lightning strikes on a beach, it will fuse the sand particles together, creating glass.

11. Magnetism While electricity is caused by the movement of electrons, magnetism is caused by the “spin” of the electrons. It’s too complicated to explain why now, but suffice it to say that every electron can either spin with a value of ½ (one direction) or -½ (the other direction) Typically, an atom with an even number of electrons has half its electrons’ spins at ½ and the other half at -½.

12. Magnetism (cont.) Sometimes many electrons in a group of atoms wind up spinning the same way instead of being balanced. This causes magnetism. Transition metals are often good magnets because the “d”-block electrons are unbound and magnetize easily (because they are unpaired). Iron (or another transition metal) that is heated up and cooled in a magnetic field will become magnetic itself.

13. Connections Because both involve the motion of electrons (either linear motion or rotational), electricity and magnetism are connected in what is called electromagnetism. As an electric field moves, a magnetic field is created perpendicular to it. As a magnetic field moves, an electric field is created perpendicular to it.

14. Right-Hand Rule Make a “thumbs-up” sign with your right hand. Imagine the direction your thumb is pointing is the direction the electricity is moving. The direction the magnetic field is moving will be the direction your fingers are curling. It’s called the right-hand rule, and the opposite (thumb-magnetic; fingers-electric) is true!

15. Electromagnetism as a Force It may seem that electricity and magnetism are very weak forces. However, think of your refrigerator. You likely have magnets holding up pictures on it. These magnets are very small, but can still hold themselves and other objects up against the pull of gravity. Compared to gravity, the electromagnetic interaction is very strong.

16. Coulomb’s Law Much like the Law of Gravitation, the distance between charged particles greatly affects the force of electromagnetism. However, unlike gravitation, the mass of the particles has no bearing on the force of electromagnetism. Instead, the charge of the particles (along with the distance) determines the strength of the electromagnetic force.

17. Opposites Attract! Unlike gravitation – which is always attractive – electrostatic force can be attractive or repulsive. Much like the overused trope in sitcoms, oppositely- charged particles attract one another. (e.g., a positive and a negative charge have an attractive force) Similarly-charged particles repel one another. (e.g., two positive charges or two negative charges have a repulsive force) Other than the sign (+ for attractive, - for repulsive), there is no effect on the strength of the force: only on the direction.

18. Coulomb’s Law (cont.) F e = k e * (q1*q2) d 2 F e is the electrostatic force q1 and q2 are the charges of the particles d is the distance between the particles k e is Coulomb’s constant; it functions in mostly the same way that the gravitational constant does, though it is a lot bigger, indicating that the electrostatic (and thus electromagnetic) interaction is much larger. – The value of k e is ~8.99x10 9 N*m 2 /C 2

19. Relationships Charge and electrostatic force have a directly proportional relationship. – This means as charge increases, force increases; it is similar to mass and gravitational force! Distance and electrostatic force have an indirectly proportional (or inversely proportional) relationship. – This means as distance increases, force decreases; it is identical to distance and gravitational force! – Notice that in this formula (as in the Law of Gravitation), distance is squared. – Because of this, the inverse-square law applies to the electrostatic force as well. – As distance decreases, electrostatic force increases exponentially.

20. Volume Notice that for both gravity and electrostatic force, volume has no effect whatsoever Assuming the charges are the same, a very large object will have the same force (gravitational or electrostatic) on another object that a very small object does.

21. Mass While mass has a large effect on the gravitational force, it has no bearing on the electrostatic force. A very massive object will attract other objects through gravitation much more than a less massive object, but will not attract/repel other objects any differently through electrostatics than a less massive one.

22. Field Lines Whereas gravitational field lines run straight toward the source, electric and magnetic fields run in a curve-like manner.

23. Electric Field between opposite charges - attractive

24. Electric field between similar charges - repulsive

25. Magnetic Field between opposite poles - attractive

26. Magnetic Field between similar poles - repulsive

27. Gravitational Field – always attractive

28. Try it out! If two particles have opposite charges and both have mass, what are the gravitational and electrostatic charges between them? If two particles have opposite charges and neither has mass, what are the gravitational and electrostatic charges between them? If two particles have similar charges and both have mass, what are the gravitational and electrostatic charges between them? If two particles have similar charges and neither has mass, what are the gravitational and electrostatic charges between them?