1. Chapter 32: Electrostatics
Conceptual Physics
Bloom High School

2. 32.1 Electrical Forces and Charges
Electrostatics- electricity “at rest”
Electrical forces- like gravity, can attract
Unlike gravity, can also repel
Charge- electrons (-), protons (+)
1. Every atom has a (+) nucleus surrounded by (-)
2. All (-) are identical in mass and charge
3. All (+) are identical in mass and charge. The nucleus also contains neutrons, which are neutral. A proton is equal in mass to a neutron, but 2000x more massive than (-)
4. Neutral Atoms have an equal number of (-) and (+)

3. Like attracts like (only in chem)
Like charges repel, opposite charges attract

4. 32.2 Conservation of Charge
Conservation of Charge- electrons may not be created nor destroyed!
Protons cannot be gained or lost from an atom
Electrons are only gained or lost in whole number quantities
There’s no such thing as losing 1.5 electrons!
Anion- an atom that has gained one or more (-)
Negative ion
Cation- an atom that has lost one or more (-)
Positive ion

5. 32.3 Coulomb’s Law Universal Gravitation (Ch 12) Coulomb’s Law (Ch 32)
Fg=G(m1m2)/r2
G=6.67x10-11 Nm2/kg2
m=mass of an object (kg)
r=distance between objects (m)
F=gravitational force between particles (N)
Coulomb’s Law (Ch 32)
Fe=k(q1q2)/r2
k=9x109 Nm2/C2
q=charge on a particle (C)
r=distance between particles (m)
F=electrostatic force between particles (N)

6. Coulomb’s Law Force is inversely proportional to distance
Larger r=weaker F
q can be positive or negative
Allows for an attractive force is q’s are opposite
(+q)(+q)  +F and like charges repel!
(-q)(-q)  +F and like charges repel!

7. Comparison of Fg and Fe For a Hydrogen atom:
Fe=k(q1q2)/r2
qe=-1.6x10-19 C
qp=1.6x10-19 C
r=5.3x10-11 m
Fe/Fg=2.2x1039 stronger!!!
Fe=8.2x10-8 N
Fg=G(m1m2)/r2
me=9.1x10-27 kg
mp=1.7x10-31 kg
Fg=3.7x10-47 N

8. 32.4 Conductors & Insulators
Conductors- outer electrons are not well fixed to the nuclei and are free to travel
Heat and electricity can be transmitted
Most metals, “salt”-based solutions
Insulators- outer electrons are fixed
No energy can be transmitted
Ceramics, rubber, dry wood, pure water

9. Semi- & Super- conductors
Semiconductors- can behave as a conductor or insulator
Germanium, silicon
Used in circuit boards
Superconductors- transmits energy without resistance (heat)
Only occurs at temperatures near 0K
Limited applications due to low temperature required

10. 32.5 Triboelectricity Triboelectricity- charging by friction
Walking across a carpet and touching a door knob
Rubbing a balloon on your head and sticking it on a wall

11. 32.6 Charging by Induction
A charge is drawn away from a pair of touching objects, then the objects are separated
Induced- when something is forced to occur
Grounding- allowing a charge to flow into the Earth

12. 32.7 Charge Polarization
Electrically Polarized- when one side of a molecule has a larger electron cloud than the other
By design or by induction

13. Summary of Causes of Charges
1. By friction, through rubbing objects together
2. By contact, through touching of a charged object to another conductive object
3. By induction, bringing a charged object near another object, but not necessarily with touching