You have 2 moles of a mono-atomic ideal gas in a container – fitted with a piston. V, P, T are the volume, pressure, and temperature. Compress the gas very fast adiabatically to half the initial volume Vf=V/2. Then let the gas expand isothermally (constant temperature) back to the original volume. The final pressure is …

1. Pfinal = P2. Pfinal = 2P3. Pfinal = ½ P

4. Pfinal > P5. Pfinal < P6. other

QUIZ

Electric charge

• First we look at some of the phenomenon, later processes/descriptions etc.– Charges – attractive-repulsive phenomenon– Insulators and conductors– Charging something– Grounding– Induction– Polarization

Read a textbook

• Understanding Physics is on Blackboard• Knight/Tipler

The charged phenomena result from the movement of charged particles (No, it’s not magic). The descriptions of the historical experiments and figuring out the mechanism behind them helps us develop intuition about how these charged particles interact with each other.

Simulationshttp://phet.colorado.edu/simulations/sims.php?sim=Balloons_and_Static_Electricity

Electric Charge

Electrostatic Rules1. Opposite charges attract. Like charges repel.2. The greater the charges, the stronger the

attractive or repulsive force between them.3. The closer the charges, the stronger the

attractive or repulsive force between them.

Writing the math in symbols

F ∞ Q1 Q2

F ∞1ror

1r2 ....

Model of an Atom

Insulators and Conductors

Metals are materials in which some or all of the valence electrons become unbound from their nuclei. These free electrons then form an electron sea—a reservoir of electrons that are easily able to flow through the metal. So, metals are conductors.

An insulator, by contrast, is a material through which charge does not flow easily. A chunk of carbon (such as coal) is an example of an insulator.

While metals are typically used to conduct electricity in electrical devices and transmission lines, many other materials are conductors as well. – each neuron in your brain contains conductive

membranes, so that ions can flow easily across them. – And tap water typically contains impurities (such as

salts) that are easily ionized, so is also able to conduct electricity.

Charge versus charged particles

• The net charge is typically the mismatch between the number of positive and negative charged particles.

• For an uncharged rod, it still physically has charged particles in it; just that the number of positively charged particles perfectly matches the negatively charged particles.

Electroscope

Consider a electroscope that already has some excess electrons on it. Now if I bring a negatively charged rod near the top of the electroscope – but do not touch it to the electroscope, the “hands” of the electroscope

would ….

1. Deflect less (collapse)2. Deflect more3. No change

Consider a electroscope that already has some excess electrons on it. Now if I bring a negatively charged rod near the top of the electroscope – but do not touch it

to the electroscope. Now I take it away – again, no touch anywhere. After removing the rod, the hands of

the electroscope ….

1. Remain more deflected2. Go back to original deflection3. Are less deflected than original4. Deflect even more

Consider a electroscope that already has some excess electrons on it. Now if I bring a negatively charged rod

near the top of the electroscope – and accidentally touch it to the scope. Now after removing the rod, the

hands of the electroscope ….

1. Remain more deflected2. Go back to original deflection3. Go back, but are less deflected than original4. Increase the deflection even more

Conservation of charge

• Charge cannot just disappear – because charged particles cannot just disappear – In a closed system, i.e. if you are not adding or removing

electrons/protons, then the net charge in the system cannot change

– In order to change the net charge, you must be adding or removing some of the charged particles; specifically, adding/removing more of one kind than the other.

– It could happen that the positive and negative charge together produce a net charge of zero.

Polarization and Induction

Science and everyday reasoning

• Duke University Mechanical Engineering researchers – explain how the lotus leaf keeps off the water from its surface – designing experiments taking inspiration from how he saw the leaf shake in the wind ….

http://www.nytimes.com/2009/10/27/science/27lotus.html?_r=1&scp=1&sq=%2btechnology+%2bengineering&st=nyt

HW corrections on website

Pickup your 1st exam regrade at the end of lecture

• David Blumenstyk• Scott Beverly

Pick up your HW from me at the end of lecture

• Avi Prince• Preetha Gautam• Jeffrey Braun

Grounding

• The earth is a very large object – sort of can take in any amount of excess charge … so if I connect something with a wire/conductor to the earth/ground, all the unbound/free charge would go into the ground – this is called grounding.

Coulomb’s Law

F =kq1q2

r2

The electrostatic constant k has been experimentally determined to be, in S.I. units,k = 9.0x109 N•m2/C2.

Units, electron charge, quantization

A dust particle of charge +1 pC sits near a small bead of charge +100 pC. Which of the following is true?

1. The force on the dust particle is more than the force on the bead of charge

2. The force on the bead is more than that on the dust particles

3. The bead exerts a force on the dust particle; There is no force on the bead itself

4. The force on the bead equals that on the dust particle

Due to their electrostatic repulsion, the dust particle and bead move apart. Intuitively, which

object (if either) gains speed more quickly?

1. The dust particle2. The bead3. They gain speed at the same rate

Three charges: 8q, -2q, +q – Where should we place the +q?

Van de Graff generator: moving?

Two charges 2q, 5q, 3q. Direction of net force on 3q.