protons (positive charge) and electrons (negative charge) carry an electric charge allowing them to have attractive forces between them
electric charge
charge of a proton/electron 1e
e=1.6*10^-19C for coulombs
e=1.6*10^-19C for coulombs
elementary charge
removed or added electrons
forms cations and anions
forms cations and anions
ionized atom
q or Q is charge
in discrete amounts of n
q=n(±e)
n is the number of charged particles (electrons)
in discrete amounts of n
q=n(±e)
n is the number of charged particles (electrons)
charge is qantized
two charged particles (q1 and q2) are a distance of r results in an electric force FE along a line
FE positive means they repel each other
FE negative means they attract each other
FE positive means they repel each other
FE negative means they attract each other
coulomb’s law
equals 10^-7 times speed of light squared
coulomb’s constant
the net electric force on a charge (q) due to a collection of other charges (Q) is equal to the sum of the individual forces that each of the Q’s alone exert on q. force felt if two or more charges are present
principle of superposition
find force felt on q by Q1 then find force felt on q by Q2 and sum the forces
How to solve for principle of superpostion
the space around a charged object in which another charged object experiences an electric force
a charge always creates an electric field whether or not another force is present
ie some source charge creates an electric field which can exert a force on another charge
a charge always creates an electric field whether or not another force is present
ie some source charge creates an electric field which can exert a force on another charge
electric field
the charge creating the electric field
E=kQ/r^2
where Q is the charge creating the field
E is the field
E=kQ/r^2
where Q is the charge creating the field
E is the field
source charge
it’s a vector field ie each point around source charge is associated with a specific vector
vector length tells magnitude or strength and direction
longer when closer to source, shorter further away from source
electric vectors always point away from positive source charges and toward negative ones
closer to source charge, stronger the resulting electric force a test charge would feel
vector length tells magnitude or strength and direction
longer when closer to source, shorter further away from source
electric vectors always point away from positive source charges and toward negative ones
closer to source charge, stronger the resulting electric force a test charge would feel
electric field terms
it takes two charges to create an electric force
it only takes one charge (source charge) to create an electric field
it only takes one charge (source charge) to create an electric field
electric field vs electric force
where r is the any point in space you want to know the electric field vector strength
positive E means Q is a positive source charge and electric field vector points away from Q. negative E means source charge is negative and electric field points towards source charge
different directions
-i means opposite direction and +i means positive direction
positive E means Q is a positive source charge and electric field vector points away from Q. negative E means source charge is negative and electric field points towards source charge
different directions
-i means opposite direction and +i means positive direction
can use coloumb’s law to determine strength of electric field
F is the force felt by a charged particle q in an electric field from source charge Q
where E is the electric field from Q
q is the charge of q that feels the force from the field
where E is the electric field from Q
q is the charge of q that feels the force from the field
Electric force and field formula
a pair of equal but opposite charges
electric dipole
two charges both act as source charges
dense lines mean strong field
spread out lines means weaker field
dense lines mean strong field
spread out lines means weaker field
2 overlapping electric fields
to find the electric field strength at a point between the charges
1. find the electric field it feels by one charge E+=kQ/r^2
2. find the force it feels by the other one E-=kq/r^2
3. add electric fields together
E=E+ plus E-
1. find the electric field it feels by one charge E+=kQ/r^2
2. find the force it feels by the other one E-=kq/r^2
3. add electric fields together
E=E+ plus E-
formula for 2 overlapping electric fields
material that contain charges that are free to roam throughout the material
ex: metals where e- are free to roam
ex: solution with lots of dissolved ions like saltwater
ex: metals where e- are free to roam
ex: solution with lots of dissolved ions like saltwater
conductors
dielectrics
don’t have free charges because electrons are tightly bound to their atoms and can’t roam freely
ex: rubber, glass, wood, paper, plastic
don’t have free charges because electrons are tightly bound to their atoms and can’t roam freely
ex: rubber, glass, wood, paper, plastic
insulators
the electrons feel a tug causing a partial negative and partial positive charge
ex: take a comb and running it through hair picks up electrons. can cause a polarized shift in paper to pick it up with the comb
ex: take a comb and running it through hair picks up electrons. can cause a polarized shift in paper to pick it up with the comb
polarized
a scalar point in space around a source charge
no direction
no direction
electric potential
Q is source charge (C for coulomb)
at any point that’s a distance r (meter m) from Q
r is not squared like for vector
V is the electric potential (in volt V or J/C joule/coulomb)
k is a constant 9*10^9 N*m^2/C^2
at any point that’s a distance r (meter m) from Q
r is not squared like for vector
V is the electric potential (in volt V or J/C joule/coulomb)
k is a constant 9*10^9 N*m^2/C^2
electric potential formula
the formula if a charge moves from one point to another point in the electric field.
the change in potential energy of a charge q that moves between two points who’s difference is ΔV
or V which is the change in potential known as the voltage
the change in potential energy of a charge q that moves between two points who’s difference is ΔV
or V which is the change in potential known as the voltage
change in electrical potential energy formula
measures the word done by the electric field as the charge moves. object moves in gravitational field
Work done by electric field
W(by electric field)=-ΔPE(elec)
where it’s opposite.
pay attention to negative sign
where it’s opposite.
pay attention to negative sign
equation for work done by an electric field
ΔKE=-ΔPE where fundamental formula for PE changes in an electric field
ΔPE=qΔV
ΔPE=qΔV
mechanical energy of electric field
to find the potential in an electric field that’s created by more than one charge
1. find potential at one point (A) due to q1 such that V1=kq1/r1
2. find potential at other point (B) due to q2 such that V2=kq2/r2
3. add together V=V1+V2
4. Do the same thing for other point B
1. find potential at one point (A) due to q1 such that V1=kq1/r1
2. find potential at other point (B) due to q2 such that V2=kq2/r2
3. add together V=V1+V2
4. Do the same thing for other point B
principle of superposition for electrical potential
