Transcript Electrostatics and Electric Fields

Electrostatics and
Electric Fields
Parts of an atom
Nucleus (protons, neutrons)
Electrons
Protons are positive (+)
Electrons are negative (-)
The force that holds atoms together is
the strong nuclear force.
 There are four fundamental forces in
nature.
1. Gravitational
2. Electromagnetic
3. Strong Nuclear
4. Weak Nuclear
Many items in nature are conserved- this
means they cannot be destroyed.
Mass, energy, momentum, and charge.
 Charge (q or Q) measured in a unit called
Coulombs (C).
 The charge on an electron or proton is
the same, 1.602 E-19 C.
 Charges of like signs repel.
 Charges of opposite signs attract.
 Neutral atoms have equal numbers of
protons and electrons.
 Electrons are able to move from one
place to another, protons are not.
 Coulomb’s Law- The Force that exists
between two charged particles depends
on the amount of charge on each and the
distance squared between them.
 Fe = kq1q2/ r2
k = 9 E9 Nm2/C2
 F ~ qq If charges change, force
changes the same way.
 F~ 1/r2 If distance increases, force
decreases. Ex: if r doubles, F=1/4
original force.
Charge Transfer
 Charges can be transferred 3 ways
 Conduction (Friction and Contact)
 Induction (nearness of charged objects)
 Polarization (temporary realignment)
 Conductors- allow electrons to move
freely, usually charge will sit on the
surface.
 Insulators- charges are more tightly
bound. Even charge distribution.
 Semiconductors- usually mixed with an
alloy to turn an insulator into a conductor.
 Superconductors- very low resistance to
the flow of charge at certain temps. Can
conduct electricity without heating.
Electric Fields
 Electric Field- a region in space where an
electric force can be detected.
 E = Fe/q
E = kq/r2 Unit: N/C
 Electric Field and Electrostatic Force are
vectors, the direction matters!
 Electric Field lines are drawn from a
positive toward a negative.
+
-