METERS

Ammeter-- measures current in (Amps --A)  

and is ALWAYS connected in series

Voltmeter--measures potential in volts and is

ALWAYS connected in parallel

OHM'S LAW

The RATIO of voltage drop V across an Ohmic resistor as compared to current i through the resistor is a constant R.

R = a constant value of V / i !

KIRCHOFF'S CURRENT RULE

The sum of the currents approaching a connector = the sum of the currents leaving a connector.   For the diagram below, i1 + i2 = i 3

KIRCHOFF'S LOOP RULE

KIRCHOFF'S RULE for SERIES RESISTORS

Resistors in series will act as a single resistor. That single resistor will equal the sum of the individual resistors.

 All resistors in series operate at the same current.      

KIRCHOFF'S RULE for PARALLEL RESISTORS

For resistors in parallel, total resistance is      

All resistors in parallel operate at the same VOLTAGE.

CAPACITORS IN CIRCUITS

       q = CV     For series: 1/C = 1/ C1 + 1/C2 + 1/C3 + etc.     q is the same!

                        For parallel: C = C1 + C2 + C3 + etc.    V is the same!

RC CIRCUITS

      For RESISTOR -CAPACITOR loops, the capacitor is most dominant after a long time when the current becomes zero in the branch of the loop with the capacitor. The value of "RC" is the time constant needed to reach 63% of the maximum charge.

LR CIRCUITS

For INDUCTOR- RESISTOR loops, the inductor is most dominant at the start of current flow when a switch is connected. At this time (as t approaches zero), the inductor controls the change in current and minimizes the growth of i. The inductor is also most in control when a switch is opened in a loop and current is decaying. Because of Lenz's Law the inductor seeks to prevent change in the status of "i", the current.