Elecricity Flashcards
Forces between charges
Opposite attract Same repel Electrostatic force either attractive or repulsive Gravitational force is always attractive Electrostatic force is conservative
SI units of charge
Coulomb, e=1.60*10^-19 C
Coulomb’s law
Magnitude of electrostatic force between two charges separated by distance.
Formula for electrostatic force
F=k(q1q2)/r^2
K- coulomb’s constant=8.9910^9 Nm^2/C^2
K=1/(4pi€0)
€0- permittivity of free space=8.8510^-12 c^2/Nm^2
Electric field formula
E=F/q0 require presence of test charge
E=k*q/r^2 dn need presence of test charge, but need to know the magnitude of the source chage
Stationary test charge
q0
Charge placed in the electric field
Stationary source charge
Charge that set up an electric field
Direction of electric field
Direction of positive test charge if source charge is presented
If source charge is +, repel away
If source charge is -, accelerate towards
Electric field lines
Lines of force
Away from +, end up on - charge
When they are closed to each other, field is stronger. When they are farther apart, field is weaker
Total electric field
Every charge will exert its own electric field
Net electric field is a vector sum of all electric fields
E total=E1+E2…..
Force on the test charge placed in electric field
F=q0/E
Need to use sign on the charge
If +, F in the same direction with electric field
If -, F in the direction opposite to the field vector.
Electric potential energy formula
U=kqQ/r
If charges are like, U +. Less stable situation. U is increasing.
If charges are unlike, U-. More stable situation. U is decreasing.
U=W=Fd= Fr=(kqQ/r^2)*r=kqQ/r
In general, a charge will always move in whatever direction in a crease in the system’s electric potential energy.
Electric potential energy definition
Work necessary to move a test charge from infinity to a point in space in a electric field surrounding a source charge.
Electric potential
V, volt, 1 J/C, scalar, sign = sign of charge
- ratio of magnitude of charge’s electric potential energy to magnitude of charge
- work that is necessary to move charge from infirmity to a point in electric field to magnitude of charge
Electric potential formula
V=W/q, W=kqQ/r
V=kQ/r
For collection of charges V total= V1+V2….
Potential difference between two points that are at different distances from the source charge
Vb-Va = Wab/q
Wab - work need to move test charge between a and b
- depends only on potentials at point a and b
- independent of the pathway between a and b
Movement of charges in potential difference or voltage
Positive charge moves spontaneously from high voltage to low voltage.
Negative charge moves from low voltage to high voltage.
High potential end in the battery is plus
Low potential end in the buttery is minus
Equipotential line
Potential difference between any two points is zero on this line
Concentric circles surrounding source charge
No work is done when move a charge between two points on equipotential line
Work will be done when move from one line to another
Work does not depends on path
Electric dipole
Results from two equal and opposite charges being separated a small distance from each other
Can be transient and permanent
V= (kqd/r^2)cos terra
qd - dipole moment p (Cm), vector
Direction of dipole moment vector
In physics from negative to positive
In chemistry from positive to negative
Dipole axis goes along distance between dipoles
Perpendicular bisector of dipole
Equipotential line that lies between two charges
Angle between it and dipole axis is 90, cos of 90= 0
Electric potential along this line is 0
The magnitude of electric field here E=(1/4pi€0)*(p/r^3)
Electric field vector will be opposite to p
Torque about the center of dipole axis
Generated by uniformed electric field where dipole places
=(qd)Esin terra
Uniformed electric field
Strength of field is the same everywhere
