Lecture 4 Flashcards
Coulombs Law
F= k (q1q2)/r^2
k = 9x10^9 N*m^2/C^2
Charge of 1 e
1.6 x 10^-19
Field
condition is space that creates a force on a charge
any force must be in contact except for gravity, electricity, and magnetism
Lines of force
represents field, point in direction of field (positive to negative)
distance between lines indicates strength of field (closer together means stronger field)
Electric field
E, electrostatic force per unit charge
E= k (q1/r^2)F
Force in electric field
Force on a charge q in electric field
F= qE
Potential energy of a charge
U= qEd
d- displacement
Voltage
potential for work by an electric field in moving any charge from one point to another
V=Ed
Voltage due to point charge
V= k (q1/r)
equipotential lines
movement perpendicular results in no change in potential
points are at same voltage
electric dipole
two opposite charges with equal magnitude
p=qd
points in direction opposite to the electric field
conductors
electrons flow freely
resistors
poor conductors, hold electrons tightly in place
current
moving charge, in amps or C/s
direction of movement of positive charge
What affects resistance
Increasing length of wire increases distance
increasing area (increasing radius) decreases resistance
Resistance
measure of an object of certain size/shape to resist the flow of charge
in Ohms
R= (resistivity)(L/A)
length/area
How does resistance vary with temperature
R= R0 [1+ alpha (T-t0)]
increase in temperature leads to increase in resistance
Ohms Law
V=IR
V= voltage/potential difference
capacitor
temporarily stores energy in a circuit
stores energy in the form of separated charge
separation creates an electric field
parallel plate capacitor
two places of conductive material separated by a small distance
one holds positive, other holds same amount of charge but negative
electric field is constant everywhere between plates
Electric field of parallel capacitor
E= (1/k)(Q/AE0)
k= dielectric
q= charge on plate
Dielectric k
k= 1/(4piE0)
substance between the plates of a capacitor
acts like a insulator and resists formation of electric field
capacitance
ability to store charge per unit of voltage
high capacitance can store a lot of charge art low voltage
C=Q/v
Charge in parallel plate
charge is proportional to area, charge is on surface so thickness does not matter
father separated means greater voltage and lower capacitance
Parallel plate capacitance equation
C= k (AE0/d)
C increases as area increases and as distance decreases
Energy stored in a capacitor
U=1/2 QV
Q=CV
In series
any two components NOT separated by a node
In parallel
Single components in alternate paths connecting the same nodes
Resistors in series
Charge drops each time it passes and dissipates energy
Reff= R1+R2 + R3…
increasing length will increase R
Total length= sum resistors
Resistors in parallel
1/Reff= 1/R1 + 1/R2 …
area= sum of area, increasing area will decrease resistance
voltage drop is the same, have lower resistances to pass through
Capacitors in series
1/Ceff= 1/C1 + 1/C2….
increasing distance will decrease capacitance
distance total= distance between first and last capacitor
Capacitors in parallel
Ceff= C1 +C2…
area= sum
increasing area will increase capacitance (can spread out and have smaller repulsive)
Ammeter
measures current flowing through a circuit
uses series of circuit
R=0 to maximize current
Voltmerer
measures potential difference between two points
attached at two points on circuit in parallel
does not draw current - infinite resistance
multimeter
ammeter and voltmeter
switch to determine
magnetic field
measured in tesla, created by moving charges
magnetic field lines
north to south
magnets in field
force pulls south pole opposite direction of magnetic field lines, north in same direction as lines
What does changing an electric field do
creates a magnetic field
AND Changing a magnetic field creates an electric field
Magnetic force
experienced by a charge moving through a magnetic field
perpendicular to velocity and magnetic field
F=qvBsin theta
