Electrostatics & Magnetism Flashcards
What kind of force is gravity always?
Attractive
Why static charge more significant in drier air?
Lower humidity makes it easier for charge to become & remain separated
SI unit of charge
Coulomb
Fundament unit of charge
e= +/- 1.6 x 10^-19 C
Law of conservation of charge
Charge cannot be created or destroyed
What are characteristics of insulators?
Electrons near the nucleus
Usually nonmetals
Can be used as dielectric materials in capacitors
How do negative charges distribute around conductors?
Evenly over entire surface
Coulomb’s Law
Quantifies the magnitude of electrostatic force between charges
F=kq1q2/r^2
Coulomb’s constant/electrostatic constant
1/4(pi)E0
8.99 x 10^9 Nm^2/C^2
Permitivity of free space
8.85 x 10^-12 C^2/Nm^2
Which is larger gravitational or electrostatic force?
Electrostatic (by about 2.5 x 10^39 larger
Q
Source charge that creates the electric field
E
Electric field
q
test charge that is placed into the electric field
Equations for electric field
E=Fc/q=kQ/r^2
E in N/C or v/m
Electric force within an electric field
F=qE
Field lines
Imaginary lines that represent how a positive test charge would move in the presence of the source charge
If the test charge within a field is positive, then the force will point?
In the same direction as the electric field vector of the source charge
If test charge within the field is negative, then the force will point?
Opposite to the field vector of the source charge
Electrical potential energy
Dependent on the relative position of one charge with respect to another charge or to a collection of charges
U=kQq/r
Another way to define electric potential energy
The amount of work necessary to bring the charge from infinitely far away to that point within the field
If charges are like charges, potential energy will be?
Positive (inverse stability to distance)
If charges are opposite, potential energy will be?
Negative (direct stability to distance)
What causes more electrical potential energy?
Like charges moving together or Unlike charges moving apart
How do you find an individual charge amount
Multiply the +/- amount times the fundamental unit of charge
Electrical potential
Ratio of the magnitude of a charges’s electricsl potential energy to the magnitude of the charge itself
V=U/q in Volts (J/C)
Electrical potential without the test charge
V=kQ/r
What is the electrical potential for positive & negative source charges?
Positive & negative
Voltage/Potential difference
Delta V= Vb-Va=Wab/q
Which way will a positive test charge move?
From high to low electrical potential to decrease electrical potential & decrease electrical potential energy
What will be the voltage of a positive test charge as it moves?
Negative, in order to decrease electrical potential energy
Which way will a negative test charge move?
From low to high electrical potential to increase electrical potential & decrease electrical potential energ
What will be the voltage of a negative test charge as it moves?
Positive,
Negative work/Negative q gives positive voltage so that potential energy is still decreasing
Other equations for electrical potential energy (U)
U=q x DeltaV
U= qEd
Equipotential line
A line on which the potential energy at every point is the same, the potential difference between any two points on the line is zero
What will change the electrical potential involving equipotential lines?
Moving from one equipotential line to another, no work done on a single equipotential line)
Electric dipole
Results from two equal and opposite charges being separated a small distance d from each other
Dipole electrical potential
V=kqdcos/r^2
d=distance between two charges
r= distance between dipole center & a single point
Dipole moment
p=qd
How do physicists define the direction of dipole moment?
from negative to positive charge
Perpendicular bisector of the dipole
The plane that lies halfway between +q & -q
Electrical potential at any point along this line=0 bc cos90=0
Magnitude of the electric field o the perpendicular bisector of the dipole
E=1/4(pi)eo x p/r^3
Which direction will the electric field vectors point along perpendicular bisector?
Opposite to p
Net torque on the dipole
t=pEsin
Equal to (d/2)Fesin + (d/2)Fesin
Allows dipole to reorient itself so that its dipole moment aligns with electrical field
Dipole has what kinds of equilibrium
Translational but not rotational
Electric potential between 2 plates
V=Ed
SI unit for magnetic strength
Tesla (T)= 1 Ns/mC
Sometimes use gauss, 1 T=10^4 gauss
Magnetic field
Created by any moving charge
Diamagnetic material
Made of atoms with no unpaired electrons and that have no net magnetic field
Slightly repelled by a magnet
Paramagnetic materials
Have unpaired electrons & become weakly magnitized in the presence of of an external magnetic field
Ferromagnetic materials
Have unpaired electrons and permanent atomic magnetic dipoles & orient randomly so material has no magnetic dipole until exposed to magnetic field & become Strongly magnitized
Examples of paramagnetic materials?
Aluminum, copper, gold
Examples of ferromagnetic materials
Iron, nickel, cobalt
Magnetic field on a straight, current carrying wire
B=uo(I)/2pi(r)
B=magnetic field
uo=4pi x 10^-7 Tm/A
Where does the thumb point in the right hand rule for magnetic field on a straight wire?
In the direction of I
Magnetic field at the center of a circular loop of wire
B=uo(I)/2r
Lorentz force
Sum of electrostatic & magnetic forces acting on them at the same time
Magnetic force
FB=qvBsin
What happens if a charge moves parallel or anitparallel to the magnetic field vector?
NO magnetic force
Which direction should you point the thumb for magnetic force right hand rule?
Along the force
Fingers toward velocity
Palm towards field
Which will always be perpendicular in magnetic force?
v and magnetic force
Magnetic force created by a current carrying wire
FB=ILBsin
theta=angle between L & B
