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Equations - Electricity

Direct Current

I = Current in Amperes (Amps)

V = Voltage (or Potential Difference) in Volts

R = Resistance in Ohms

W = Power in Watts


I = V/R and V = IR and R = V/I


W = I2R and W = V2/R and W = VI


The above hold good for Alternating Current only if the load is purely resistive (rare).


Resistances in Series: R = R1 + R2


Resistances in Parallel: 1/R = 1/R1 + 1/R2


Gain or Loss

Gain or Loss = 10 Log (Output Power/Input Power) = 10Log (P2/P1)

or

= 20 Log (Output Current/Input Current) = 20 Log (I2/I1)

or

= 20 Log (Output Voltage/ Input Voltage)

or

= 20 Log (V2/V1)


e.g. Power Ratios :

2 x = 3 dB approx.

4 x = 6 dB approx.

8 x = 9 dB approx.

10 x = 10 dB

100 x = 20 dB

1,000 x = 30 dB

1,000,000 x = 60 dB

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