the study of electrical charges at rest Electrodynamics Electrostatics the study of electrical charges at rest Electrodynamics the study of electrical charges in motion Charge is a property of matter.

Types and Sources of Electric Charge Electric Charges Types and Sources of Electric Charge Two kinds of electric charge – positive negative protons electrons http://www.physics.ucla.edu/~dauger/orbitals/ Quantum Mechanical Model http://csep10.phys.utk.edu/astr162/lect/light/bohr.html Bohr Model of Atom Materials with equal numbers of negative and positive charge are said to be electrically neutral.

Types and Sources of Electric Charge Ben Franklin did a great deal of experimentation in the area of electricity. However, Ben Franklin chose the wrong sign convention for charge – it has stuck ever since.

Properties of Electric Charge Charge is quantized. Positive and Negative charges have same magnitude e = p = 1.6 x 10-19 C SI unit of charge is the Coulomb Charge is conserved.

Electrons are free to move Electrons are bound to the atoms Atoms and Materials Different elements will have different types of bonds – different strengths. Classification of Materials – Conductors, Insulators, Semiconductors Conductors Electrons are free to move about the material Insulators Electrons are bound to the atoms - can’t move (conduct).

How do we charge an object? A. Tribocharging - Charging by rubbing When you rub a rubber rod with fur electrons are transferred from the fur to the rod. The rod becomes negatively charged and the fur becomes positively charged.

Electrostatic Voltages Positive (+) Air Human Hands Rabbits Fur Glass Human Hair Mica Wool Cats Fur Silk Aluminum Paper Cotton Rubber Balloon Hard Rubber Gold/Platinum Polyester Vinyl Saran Wrap Negative (-) Triboelectric Series   Electrostatic Voltages Means of Static Generation 10 – 20 % Humidity 65 – 90 % Humidity Walking across carpet 35,000 1,500 Walking across vinyl floor 12,000 250 Worker at bench 6,000 100 Vinyl envelopes for work instructions 7000 600 Common poly bag picked up from bench 20,000 1,200 Careful when you fill up your gas tank!

Insulators & Conductors Insulator is a substance that does not allow the electrons to freely move. Conductor is a substance that does allow the electrons to freely move

Conductive Properties of Solids metal alloys special metals silicon wood rubber sea water pure water SUPER CONDUCTORS SEMI INSULATORS CONDUCTORS CONDUCTORS Conductors allow charge to flow through them easily high conductivity Insulators inhibit charge flow high resistivity

There is no charge on the inside wall of a hollow electrified conductor. Charge tends to concentrate on the pointed regions of a conductor.

How do we charge an object? B. By Conduction – Transfer of Charge by Direct Contact No matter what the shape of the conductor, excess charge always resides on its outer surface.

This works best when two INSULATORS are rubbed Friction This works best when two INSULATORS are rubbed against one another

Conduction Negative To Neutral - - Excess electrons exert repulsive forces on one another, causing them to move apart as much as possible BOTH now have the same charge!

Conduction Positive To Neutral + + Electrons in the neutral object experience an attractive force. They neutralize some of the positive charge, leaving both with a lack of electrons BOTH now have the same charge!

How do we charge an object? C. Induction – Inducing a charge without touching. Conductors Charging by induction (two conductors) Charging by induction (1 conductor and ground) Charge is physically moved in/on the materials.

c. By Induction grounding

How do we charge an object? C. Induction – Inducing a charge without touching. Insulators Free Standing Atoms are randomly oriented Charge does not actually move In/on the insulator – redistributes. Polarizes the material.

Induction Negative To Neutral - Polarization + - Excess electrons exert force against nearby electrons in the neutral object

Induction Positive To Neutral + Polarization - + Electrons in the neutral object experience an attractive force, which pulls them closer to the charged object

Grounding In either case, grounding a charged object makes it neutral Since the Earth is so large it can equalize charges from other objects very easily The Earth can equalize charge by: absorbing excess electrons from negatively charged objects giving free electrons to positively charged objects In either case, grounding a charged object makes it neutral One symbol that is often used to show that something is grounded is:

- - - - - - - Electroscope An electroscope is a device that detects CHARGE - - - - - When the scope is CHARGED, the LEAVES at the bottom will REPEL one another The charged LEAVES exert force on one another, forcing them apart - -

Electroscope – negative conduction Step 5 Scope is once again neutral – excess electrons are gone Step 3 Scope is now negatively charged Step 4 Scope is grounded allowing electrons to escape Step 1 Negative rod touches neutral scope Step 2 Electrons spread out and charge plates - - - - - - -

Electroscope – positive conduction Step 4 Scope is grounded – electrons from the ground are attracted to the positive scope Step 5 Scope is once again neutral – balanced charge is restored Step 2 Electrons leave scope because they are attracted to the positive rod Step 3 Scope is now positively charged Step 1 Positive rod touches neutral scope + - + - - - - + - +

Electroscope – negative induction Step 3 Rod is removed – electrons are attracted back to the top and “re-neutralize” the electroscope. Step 2 Scope polarizes as electrons at the top try to move away from the charged rod. Step 1 Negative rod brought near grounded scope - - + -

Electroscope – positive induction Step 3 Rod is removed. Electrons are attracted back into the leaves by the protons, making the electroscope neutral again. Step 2 Electrons from the bottom of the electroscope are attracted to the positive rod – get pulled up. The leaves get a positive charge on them. Step 1 Positive rod is brought near neutral electroscope + - + - +

Electroscope – induction with ground Step 3 Ground is removed while the rod is still nearby, keeping electrons from re-entering the scope Step 5 The rod is taken away and the positive charge remains on the scope Step 4 Scope now has a charge that is opposite to the charge on the rod Step 2 Excess electrons from the rod force electrons from the scope into the ground. Step 1 Negative rod brought near grounded scope - + - - + - +

Electroscope – induction with ground Step 3 Ground is removed, while the rod is still nearby, pulling on electrons and keeping them from escaping Step 4 Scope is now negatively charged – the opposite charge as that of the rod Step 5 Rod is taken away and the negative charge remains on the scope Step 1 Positive rod is brought near grounded scope Step 2 Electrons from the ground are attracted to the positive rod + - - -