Ch 15-17 Flashcards
Insulator
electrons tightly held by the nucleus; held by covalent bonds; right side on periodic table
Conductor
electrons loosely held by nucleus; metallic left side of periodic table; really want to give up e-; typically 1 e-per atom free
Induction
inducing a charge separation in a neutral substance ; only works with attraction;
Static Electricity
friction between two objects will lead to one stealing e-s from another, and they become charged; then these extra e-s leap to be grounded at a metal door knob
Lightening
unstable air with huge updraft as a bottom part of a cloud gets charged negatively, and causes the positive charges to be drawn towards the cloud; this can cause lightening if electron attraction is strong enough
Superposition
the total F is the vector sum of the individual forces; LIKELY TO BE ON THE EXAM
Electric Field
exists in the region of space around a charged object; the force is exerted by something (the field) that is in the same location as the charged object; depends only on the charge q and the distance r from that object to a point in space
Conductor Properties
electric field is zero everywhere inside the material; any excess charge resides on the surface; E-field is perpendicular to the conductor’s surface; and the charge accumulates at sharp points
Electric Flux
a measure of how much the E-field vectors penetrated a given surface; flux lines passing into the interior of the volume are negative and those passing out of the interior are positive
Millikan Oil Drop Experiment
you can balance mg and E-field so some of the oil drops freeze/float; charge was quantized this way in units of e-
Van de Graaf
rubber steals/drops off charges when it reaches the metal; these excess charges go to the outside of a metal (best in dry conditions)
Gauss’s Law
the total electric flux leaving a closed surface is equal to the charge; can be used to find an E-field; works for symmetrical surfaces when the charge is enclosed
Potential for a point charge
k (q/r); or Ed
Relationship between work and PE
w= -PE;
Work for Electricity
W= Fd = qEd
Sign conventions of Potential
+ charges lead to + potential
- charges lead to -potential
moving towards + charges gives + V
assumes V= 0 at r = infinity
Equipotential Surfaces
potential in a conductor is constant; no work is required to move a charge at constant speed; the electric field is perpendicular to the surface;
Capacitor
capacity to hold charge; a device used for rapid release of electronic units; stores energy to be reclaimed;
Capacitance
C =Q/∆V
Parallel Plate Capacitor Capacitance
C= e A/d
Capacitors in Parallel
C = C1 + C2 + …
Capacitors in Series
1/C = 1/C1 + 1/C2 + …
Energy Stored in a Charged Capacitor
U = 1/2Q∆V = 1/2C(∆V)^2 = Q^2/2C
Dielectric
an insulating material that increases capacitance, decreases voltage, decreases E-field, and either increases or decreases energy stored
Capacitance with a Dielectric
multiply capacitance by the dielectric constant k
Current
the rate at which charge flows through this surface; represented by I
Current Density
current/area or sigmaE; also equal to E-field/resistivity
Temperature and Resistance for conductors
as temperature rises, resistance increases due to the molecules moving quicker
Temperature and Resistance of Semiconductors
As temperature increases, resistance decreases because it frees more electrons
Temperature and Resistance of Superconductors
At a certain Temperature, resistance drops to 0
Resistivity
represented by roe;
Resistance
roe times length over area
