Electrical Formula

CHAPTER 1 ELECTRICAL FORMULAS
OHM’S LAW/POWER FORMULAS

R x I2 E x I P R P E

E2 RxI R

P I P x R E I

P I E R

E R P I2

E2 P

P = Power = Watts R = Resistance = Ohms I = Current = Amperes E = Force = Volts

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OHM’S LAW DIAGRAM AND FORMULAS

E I
E = I x R I = E ÷ R R = E ÷ I

R

Voltage = Current x Resistance Current = Voltage ÷ Resistance Resistance = Voltage ÷ Current

POWER DIAGRAM AND FORMULAS

P E
I = P ÷ E E = P ÷ I P = I x E

I

Current = Power ÷ Voltage Voltage = Power ÷ Current Power = Current x Voltage
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OHM’S LAW AND IMPEDANCE

E = VOLTAGE (IN V) I = CURRENT (IN A) Z = IMPEDANCE (IN Ω)

E =IxZ

I =

E Z

Z=

E I

Ohm’s law and the power formula are limited to circuits in which electrical resistance is the only significant opposition to current flow including all DC circuits and AC circuits that do not contain a significant amount of inductance and/or capacitance. AC circuits that include inductance are any circuits that include a coil as the load such as motors, transformers, and solenoids. AC circuits that include capacitance are any circuits that include a capacitor(s). In DC and AC circuits that do not contain a significant amount of inductance and /or capacitance, the opposition to current flow is resistance (R). In circuits that contain inductance (XL) or capacitance (XC), the opposition to the flow of current is reactance (X). In circuits that contain resistance (R) and reactance (X), the combined opposition to the flow of current is impedance (Z). Resistance and Impedance are both measured in Ohms. Ohm’s law is used in circuits that contain impedance, however, and Z is substituted for R in the formula. Z represents the total resistive force (resistance and reactance) opposing current flow.

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OHM’S LAW FOR ALTERNATING CURRENT
For the following Ohms Law formulas for AC current, θ is the phase angle in degrees where current lags voltage (in inductive circuit) or by which current