AP Physics II

Current

Rate of charge flow

Current formula

I = change in Q/change in t

Units of Current

A = C/s

Electrons naturally want a —— to get to a ————-

higher potential, lower potential energy

OHMs Law

I = V/R

R = pL/A

p/resistivity value

high p = insulator

low p = conductor

p depends on the material

UNITS: ohms * m

R

a property of the object, matters how we shape it also

UNITS: ohms; V/A

p is ———

temperature dependent

AS TEMP INCREASES, RESISTIVITY DECREASES

What does it mean to be ohmic?

Unimpacted by temperature on a I vs. V

(Referred to as nonohmic if it slopes downward)→ often lightbulbs

P =

change in E/change in t (usually used for transferring from one form energy to the next)

P =(other formula)

IV (usually depends on both, so hard to work with equations)

2 derivations needed for test

V²/R (IV and substitute I = V/R) BEST FOR PARALLEL

I²R (IV and substitute V = IR) BEST FOR SERIES

For parallel resistors,

V is constant

For resistors in series

I is constant

Kirchoff Junction Rule

Iin = I out

CONSEQUENCE OF THE CONSERVATION OF CHARGE

Loop Rule Kirchhoff

V change over whole loop = 0

battery: - + to - will DECREASE BY EMF
- to + will INCREASE BY EMF
resistors (I specific): against resistor +IR

with resistor -IR

capacitors: - + to - will DECREASE BY V DIFFERENCE ACROSS CAPACITORS
- to + will INCREASE BY V DIFFERENCE ACROSS CAPACITORS

Voltage across capacitor

Vc = Q/C

Resistors in series

R = sum of Ri -same I, V=sum of V i

Resistors in Parallel

1/Rp = sum of 1/Ri -same V, I = sum of I i

Capacitors in series

1/Cs = sum of 1/Ci -same Q, V= sum of Vi

Capacitors in parallel

Cp = sum of Ci -same V, Q = sum of Qi

Tau

Req * Ceq

Time it takes to reach depends on

Tau and resistance, small T faster it approaches line

I approach, large T results in ——

longer time

Real Batteries have internal—-

resistance

Charging

C acts like ideal wire initially (transfers I)

C acts like an open switch at steady state (doesnt transfer I)

Discharging

C will act like battery w/ V = Q/C intially

C acts like an open switch at steady state

ALL CONSTANTS FOR CAPACITORS

Cp = same V

Cs= same Q

ALL CONSTANTS FOR RESISTORS

Rs = I

Rp = V

CONNECTION

p ALWAYS IS SAME VOLTAGE, Rs = I, Cs=Q