Physics 2 midterm

electron charge is…

conserved and quantized

conductors:

-outer electrons of atom are free to move from atom to atom and charges move freely

-metals

-when charge, the charge distributes over the entire surface

-electric field shields; if placed in a field the charges redistribute until the total field inside the conductor = 0

insulators

-electron associated with a particular atom and very few electrons move

-if placed in a field, dipoles form until the field inside the insulator is less than outside but greater than 0

semiconductors

-some free electrons

-electron properties can be changed by the addition of controlled amounts of certain atoms

charge by rubbing

electrons move from one object to another by contact and one becomes - the other +

induced charge

positioning an external electric charge close to a conductor will redistribute its charge

polarization

positioning an external electric charge close to an insulator makes it become dipole

which is greater induction or polarization

induction

gravitational forces …

are very small and most everyday forces are electric

is electric field vector or scalar

vector; it has both magnitude and direction

if a charge (q) is positive then the electric field (E) …

points away from the charge which is sourcing the field

if a charge (q) is negative then the electric field (E) …

points toward the charge which is sinking the field; antiparallel

if a charge (q) is positive then the electric force (F) …

is parallel to the electric field (E)

if a charge (q) is negative then the electric force (F) …

is antiparallel to the electric field (E)

what do field lines depend on

direction and strength of the field and the force exerted on the test charge

if a field is uniform the acceleration is …

constant

parallel plate capacitor

two conductive planes with area (A) parallel to each other, a storage bucket for charges, a plate connected to the hot terminal of the battery (Q+), and a plate connected to low voltage/ ground terminal of battery (Q-)

outside a capacitor the electric field (E) = …

0

electrostatic equilibrium

no net motion of charge within a conductor; E = 0

electric forces depend only on …

initial and final positions

if only conservative forces act then the Efinal = …

Einitial

work is done a charge (q) by

the electric field (E)

electric potential energy is scalar or vector

electric potential energy (Uel) is scalar, it has just magnitude

same signs make Uel …; opposite signs make Uel …

+, to bring them together

-, to keep them apart

voltage (V)

-also called electric potential

-scalar

-what a force would be if a charge was placed at any point; so it has value at any point

-independent of value of test charge and it can exist without the test charge

if V = 0 then r =

infinity

if V = infinity then r =

0

electron volt (eV)

the energy a charge acquires if accelerated by the electric forces between 2 points with the difference of 1 Volt

1 eV= |charge of e-|

equi-potential lines

lines of constant voltage perpendicular to electric field lines

if the electric field inside a region = 0 then the change in voltage =

0, its constant

electric field lines always point in the direction of …

decreasing potential energy

capacitors

store electric charge, made of 2 conductors (plates) with equal and opposite charges which create a potential difference

dielectric

nonconducting material that when placed between plates of a capacitor increase the capacitance; polar molecules

d (capacitor)

d is the maximum voltage that can be applied to a capacitor without causing a discharge and it depends on the dielectric strength of the material

how do dielectrics affect capacitance

they can increase C by increasing the maximum operating V; possible mechanical support between plates

tubular capacitor

metallic foil interlaced w/ mylar rolled into a cylinder

oil filled capacitor

high voltage; interwoven metallic plates immersed in silicon oil

electrolytic capacitor

-stores large amounts of charge at low V; conducts electricity through motion of ions

-V applied between foil and electrolyte and a thin layer of metal oxide forms and is dielectric

variable capacitors

2 interwoven sets of metallic plates, one fixed, the other moveable; the contained air is dielectric

in the absence of an electric field dielectric molecules are

dipoles and randomly oriented

describe dielectric molecules when an external electric field is applied

-a torque is produced and the molecules partially align with the field; the degree of alignment depends on temperature and the magnitude of the field

-the molecules produce an induced electrical plate opposite the original

for F=qE, if the charge (q) is - and you want the force (F) to point positive then …

E must point negative