AP Physics 2

n =..

q/e (q is charge, e is elementary charge (1.6×10^-9), and n is the numerical/integer charge)

The further the distance

the weaker the force

Conductor have weakly bound electrons to PERMIT

move freely about, array of positively charge ion cores

Induction

If an external charge is held near a conductor a charge separation will be induced in the conductor, IF CONDUCTOR IS INSULATED, THE EFFECT WILL END WHEN OBJECT IS REMOVED 

If two conductors are of the same size and shape, IN DIRECT PHYSICAL CONTACT

then charge will be transferred until each object has the SAME NET CHARGE 

Insulators can also be charged via conductors

far less

-EXCESS CHARGE will remain attached to particular atoms and can’t move around (polarized)

How to figure out overall charge when TWO spheres are in contact

ADD charges/2 - essentially average

Polarization

When an external charge is brought near a neutral atom, it will polarize and create an electric dipole

ALWAYS results in a net attractive force

Polarization in Conductors vs Insulators

Conductors - sides become charged

Insulators - polarization occurs (- +)

Induction

charging where there is no physical contact between objects, the conductors must be separated before the charge causing the polarization is removed

Grounding

Unlimited source of free electrons

Coulomb’s Law

Fe = k(q1)(q2)/r² (remember that TOP q1 and q2 are magnitudes, NOT negative)

k value (Coulomb’s Constant)

9 ×10^9, r is distance between charges and MUST BE MEASURED IN M, put a 2 if the same force is used twice 

Field 

A physical quantity that is represented by a scalar or vector that has a value at each point in space and time, property of space and does not require an object to occupy said space 

Force =

Property * Field

E = Fe/Q

Electric Field, N/C for units

When finding acceleration or mass with electric fields

USE F= MA

Motion of charges in uniform E-fields

Analogous to the motion of masses in a uniform gravitational field, uniform field will exert a constant force on the charge, motion with or against the field will result in the charge speeding up or slowing down, PARABOLIC TRAJECTORY

in these types of problems, use the kinematics equations with x and y 

Electric field due to a point charge

E = Fe/q = kqQ/r^2/q E=kQ/r² (Q is from the point we are focusing), greater charge = stronger field, inverse square relationship for distance

Right is defined as

POSITIVE, e fields act as vectors which means you add them all up OR do trig to find electric field

Capacitors

A device that is able to store the electric charge and energy, parallel plates face to face (top is almost always positive)

The electric field between the plates are uniform having the same value everywhere + formula for plate electric field 

Q/e0A (e0, related to k vacuum permittivity), SEPARATION MUST BE SMALL, AREA OF PLATE not SEPARATION

Electric field lines

TANGENT to the E-field vectors at all points, close together when stronger, MORE DENSE WHEN STRONGER, + OUT OF, - INTO

LOCATION DOESN’T INDICATE ITS CLOSENESS TO LINES THAT ARE CLOSER TOGETHER

When the charges are in electrostatic equilibrium in a conductor

the electric field inside is ZERO

If the conductor has an excess charge,

all of the charge will lie on the conductor’s surface: due to repulsive forces that the charges exert on each other

Screening

Eliminating electric fields by nulling out the inside of the enclosed void as zero, SHARPER POINTS = MORE CHARGE

Dielectric Breakdown

If the electric field within an insulating material is strong enough then the electrons can be ripped away from their nuclei: resulting in an insulator that is conducting electricity 

Force from fields

Fe = q * E

Torques on Dipoles

Fnet = 0, will rotate due to Torque, + will line up with electric fields path of motion FOR EQUILIBRIUM

for ball on string have forces equal each other ON NON MOVING SIDES to assume equilibrium

Touching a conductor

Causes a positive charge due to taking of electrons

m1m2 MUCH >

q1q2

electron and protons are

FORCE PAIRS, if F is original force and 2F is the new force of the protons, the new force of the electron is also 2F

Mass of an electron

9.11 × 10^ 31