Common Electronic And Electricity
Formulas
Below is a reference chart giving all the equations deriving from Ohm’s Law. The parameters E, I, R and P are shown in the central area, each occupying one of the four quadrants of the pie. To solve for a given parameter, find that parameter at the center of the chart and choose the equation in its quadrant that defines the quantity in terms that you have measured or know.
NOTE: Equations referring to power and impedance are describing a
Power Factor (PF), rather than pure DC power. This quantity accounts for the reactance of
the load and the AC signal.
Ohms Law (DC Current): Current in amps = Voltage in volts / Resistance in ohms = Power in watts / Voltage in volts Current in amps = (Power in watts / Resistance in ohms) Voltage in volts = Current in amps × Resistance in ohms Voltage in volts = Power in watts / Current in amps Voltage in volts = (Power in watts × Resistance in ohms) Power in watts = (Current in amps)^{2} × Resistance in ohms Power in watts = Voltage in volts × Current in amps Power in watts = (Voltage in volts)^{2} / Resistance in Ohms Resistance in ohms = Voltage in volts / Current in amps Resistance in ohms = Power in watts / (Current in amps)^{2} Ohms Law (AC Current): In the following AC Ohms Law formulas, q is the phase angle in degrees by which current lags voltage (in an inductive circuit) or by which current leads voltage (in a capacitive circuit). In a resonant circuit (such as normal household 120VAC) the phase angle is 0º and Impedance = Resistance. Current in amps = Voltage in volts / impedance in ohms Current in amps = (Power in Watts / Impedance in ohms × cosq) Current in amps = Power in Watts / (Voltage in volts × cos q) Voltage in volts = Current in amps × Impedance in ohms Voltage in volts = Power in Watts / (current in amps × cos q) Voltage in volts = ([Power in watts × Impedance in ohms] / cos q) Impedance in ohms = Voltage in volts / Current in amps Impedance in ohms = Power in watts / (Current amps^{2} × cos q) Impedance in ohms =(Voltage in volts^{2} × cos q) / Power in watts Power in watts = Current in amps^{2} × Impedance in ohms × cos q Power in watts = Current in amps × Voltage in volts × cos q Power in watts = ([Voltage in volts]^{2} × cos q) / Impedance in ohms ELECTRONIC CIRCUIT EQUATIONS: Resonant frequency in hertz (where X_{L}= X_{C}) = 1 / (2p ×[Inductance in henrys × Capacitance in farads]) Reactance in ohms of an inductance is X_{L} X_{L} = 2p(frequency in hertz × Inductance in henrys) Reactance in ohms of a capacitance is X_{C} X_{C} = 1 / (2p[frequency in hertz × Capacitance in farads] ) Impedance in ohms (series) = (Resistance in ohms^{2} + (X_{L}X_{C})^{2}) Impedance in ohms (parallel) = (Resistance in ohms × Reactance) / (Resistance in ohms^{2} + Reactance^{2} Resistors in Series (values in Ohms): Total Resistance = Resistance_{1} + Resistance_{2} + ... Resistance_{n} Two Resistors in Parallel (values in Ohms): Total Resistance = Resistance_{1} × Resistance_{2} / Resistance_{1} + Resistance_{2} Multiple Resistors in Parallel (values in Ohms): Total Resistance = 1 / (1 / Resistance_{1}] + 1 / Resistance_{2} + ... 1 / Resistance_{n}]) Capacitors in Parallel (values in microfarads): Total Capacitance in Parallel (values in any farad) = Capacitance_{1} + Capacitance_{2} + .... Capacitance_{n} Capacitors in Series (values in microfarads): Total Capacitance in Series (values in any farad) = Capacitance_{1} × Capacitance_{2} / Capacitance_{1} + Capacitance_{2} Multiple Capacitors in Series (values in farads) = 1 / ([1 / Capacitance_{1}] + [1 / Capacitance_{2}] + ...... [1 / Capacitance_{n}]) LCR Series Time Circuits: Time in seconds = Inductance in henrys / Resistance in ohms Time in seconds = Capacitance in farads × Resistance in ohms SINE WAVE VOLTAGE AND CURRENT: Effective (RMS) value = 0.707 × Peak value Effective (RMS) value = 1.11 × Average value Average value = 0.637 × Peak value Average value = 0.9 × Effective (RMS) value Peak Value = 1.414 × Effective (RMS) value Peak Value = 1.57 × Average value DECIBELS: db = 10 Log_{10} (Power in Watts #1 / Power in Watts #2) db = 10 Log_{10} (Power Ratio) db = 20 Log_{10} (Volts or Amps #1 / Volts or Amps #2) db = 20 Log_{10} (Voltage or Current Ratio) Power Ratio = 10^{(db/10)} Voltage or Current Ratio = 10^{(db/20)} If impedances are not equal: db = 20 Log_{10} [(Volt_{1} [Z_{2}]) / (Volt_{2} [Z_{1}])] Frequency and Wavelength Frequency in kilohertz = (300,000) /wavelength in meters Frequency in megahertz = (300) / wavelength in meters Frequency in megahertz = (964) / wavelength in feet Wavelength in meters = (300,000) / frequency in kilohertz Wavelength in meters = (300) / frequency in megahertz Wavelength in feet = (964) / frequency in megahertz Wavelength = speed of sound (ft/sec or m/sec) / frequency Speed of sound = 1130 ft/sec Antenna Length: Quarterwave antenna: (ordinary wire, velocity factor = 0.95) Length in feet = 234 / frequency in megahertz Halfwave antenna: (ordinary wire, velocity factor = 0.95) Length in feet = 466 / frequency in megahertz 70 Volt Loudspeaker Matching Transformer Primary Impedance = (Amplifier output volts)^{2} / Speaker Power
