Electricity and Magnetism

1
Electricity and Magnetism

• Explore the second of the four fundamental forces
  in nature
• Gravity
• Electricity and Magnetism
• Weak Nuclear Force
• Strong Force
• Huge effect on everyday life

2
Electricity and Magnetism

• The electromagnetic force is what binds electrons
  to the nuclei of atoms
• Responsible for all of chemistry
• When we liberate electrons from individual atoms,
  we can make them do work for us
• So, the topic is extremely important if we are to
  understand the world around us

3
Electricity and Magnetism

• Many of the fundamental particles have something
  we call electric charge
• We dont know what this is, we can only describe
  the results when particles have the property
• There are two kinds of charges which we call
  Positive and Negative

4
Electricity and Magnetism

• We observe that like charges repel
• We observe that unlike charges attract
• The forces are inverse square law forces, just
  like gravity, but very much more powerful
• Atoms have a positive nucleus with surrounding
  negatively charged electrons

5
Electricity and Magnetism

• Each electron in an atom is identical to every
  other electron so they all have the same mass and
  the same negative charge
• The nucleus is composed of positively charged
  protons and uncharged neutrons
• All protons are identical and the charge of the
  proton is exactly the same size as the charge of
  the electron, but it is opposite

6
Electricity and Magnetism

• Normal atoms have identical numbers of protons
  and electrons
• Atoms with a missing electron are called positive
  ions
• Atoms with an extra electron are called negative
  ions

7
Conservation of Charge

• Another important conservation law is
  Conservation of Charge
• Add to our set of tools along with Conservation
  of Energy and Conservation of Momentum
• We dont know why, but we observe it to always be
  true
• Another deep meaning that isnt simple

8
Coulombs Law

• Relationship describing the force between two
  charged particles
• Charge is measured in coulombs
• Force in newtons
• Distance in meters

9
Coulombs Law

• One Coulomb is a HUGE charge
• Takes 6.25 x 1018 electrons to amount to this
  much charge
• The constant k is 9 x 109 Nm2/C2
• Shows how huge the electric force really is

10
Coulombs Law
11
Charge Polarization

• Make a tiny difference in the average positions
  of electrons in an atom

Distorts electrons like tides on the earth and
pulls the nucleus to the right
12
Electric Field

• How do things interact with each other when they
  dont physically touch?
• Problem has occupied many great minds
• When we talked about gravity, we said that
  Einstein demonstrated that mass distorts
  spacetime and the bending of spacetime made
  objects appear to experience a force
• Can talk about a gravitational field

13
Electric Field

• Place a charged particle in spacetime and it
  creates an electric field
• Using Coulombs Law, we can calculate the force
  on a test charge at every point in space
• The force/unit charge is the definition!

14
Electric Field
15
Electric Potential

• Lift an object into the air and we give it
  gravitational potential energy

16
Electric Potential

• Separate a positive charge from a negative charge
  and give it electric potential energy

17
Electric Potential

• Define electric potential as the electric
  potential energy per unit charge