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Terms in this set (15)
Electrostatics
Electricity at rest; the study of electric charges, the forces between them, and their behavior in materials.
When materials are rubbed together they transfer loosely held e-s creating a charge build up.
Coulomb
the fundamental unit of electric charge;
1 e = 1.6 x 10^-19 C
For a proton e is +
For an electron e is -
Coulomb's Law
Law describing the electrostatic force that exists between two charges, q₁and q₂,
F = k(q1q2/r²) = qE
F in N
k in N×m²/C²
q₁ in C (pay attention to the signs)
q₂ in C
r = distance between the two centers (in m)
E = electric field in N/C
Bigger charge difference larger F btwn, larger distance btwn smaller F
Use to calculate the force a charge feels due to its proximity to another charged particles electric field
Coulomb's constant
F = k(q1q2/r²)
k = 9 x 10^9 N×m²/C²
Electric Field
a region in space around a charged object that causes a stationary charged object (test charge) to experience an electric force; strongest closest to the source charge.
Every electric charge sets up an electric field.
Magnitude of an electric field
E = F/q = kQ/r^2
E force per unit charge in N/C or V/m;
q=stationary positive test charge in C
Q= source charge magnitude C
k= electrostatic constant 9 x 10^9 in Nm^2/C^2
At any point in space a test charge can be placed and it will feel a force due to another nearby charge.
The magnitude of the force divided by the magnitude of the charge feeling the force equals the electric field.
Use F/q if referencing a test charge
Use kq/r^2 if no test charge present; r measures from source to pt where you want to know the magnitude of the electric field
E as a vector quantity
magnitude and direction;
direction: direction that the positive test charge would move in the presence of the source charge (attractive or repulsive).
- positive source charges radiate out
-negative radiate in
- field lines spread out with distance represents weakening electric field
Force on test charge
F = q₀E
Note: if charge is negative, force will be in the direction opposite the electric field vector
Net electric field
collection of charges have a net electric charge:
Etot= E q1 + E q2 + E q3...
Electric Potential Energy
the stored energy a charge has based on it's location in an electric field; work is done whenever an object moves with/against the field
U=W=Fd=kqQ/r,
use when V is due to just one other charge Q.
Amt of work necessary to bring the charge from infinity to the field pt:
(change in electric potential energy = Force x distance = q∆V = E q d)
Takeaway: when like charges are move twds each other the EPE increases and when unlikes move twds each other their EPE decreases
This is not like electric potential; this is NOT the stored energy per unit charge it IS the E associated with the charged particle (e.g. for a 3C charged particle in an electric field)
Electric Potential
Amount of electric potential energy per unit charge; the work required to bring a positive test charge q from infinity to within an electric field of another positive source charge Q, divided by that test charge.
V = (kQ)/r = W/q
V is volt;
1 V = J/C aka energy per unit charge
V is + for negative charge
V is - for positive charge
V tot = V1 + V2 +V3...
Electric Potential Difference
the amount of work required per unit charge to move a positive charge from one point to another in the presence of an electric field.
V(b) - V(a) = W(ab)/q
Equipotential Lines
Concentric circles emanating from a source charge that cross its electric field lines perpendicularly.
No work is required for a test charge to travel along the circumference of one of these since the potential at every point along that line is the same (Vb-Va= 0)
Work depends only on the potential difference NOT the path.
Electric Dipole
Electric dipole is created when two equal and opposite charges are a small distance away from each other.
Use eqn to calculate the dipole moment for a given molecule.
p= qd
p = dipole moment (C x m)
q = charge (C)
d = distance between the charges (m)
Use equation below to calculate the Electric Potential at some point P within the vicinity of the dipole.
V = kq (r2 - r1 / r1r2) = (kqd/r^2) cosθ = (kp/r^2) cosθ
V = electric potential (Volts)
k = Coulomb's const (8.99 * 10⁹ N*m²/C²)
q = charge (C)
r = distance from point P to charge
d = distance between the charges
p = dipole moment (C x m)
Perpendicular bisector of the dipole
equipotential line lies halfway between the two charges; the electric potential along this line is zero.
to get Electrical Field along this line use:
E = (1/4πε₀)(p/r³)
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