LEVEL 3 ENGINEERING PRINCIPLES - DC CIRCUITS INFORMATION AND EQUATIONS
Voltage, Current, Power and Resistance Subject Force between charged particles (Coulombs Law)
Equation
F=
k e q1 q 2 r2
Variables and Units F = [attractive or repulsive] force in Newtons (N) *1 Ke = Coulomb’s constant (Nm2C-2)
Current
Energy
I=
Q t
E = QV
*2 q = particle charge in Coulombs (C) r = distance between particles (m) I = Current in Amps (A) Q = [total] charge in Coulombs (C)
Resistance
Conductance
R= ρ
L A
A G= σ L ΔR = R o αΔθ
Voltage (Ohm’s Law)
V = IR P = Et P = VI 2
P=I R V2 P= R
Useful Constant Values: *1 Ke = 8.988 x 109 Nm2C-2 *2 qelectron = 1.603 x 10-19 C
E = energy in Joules (J) V = voltage in Volts (V) R = resistance in Ohms (Ω) ρ = resistivity in Ohm-meters (Ωm)
Change in Resistance (due to change in temperature)
Power
t = time in seconds (s)
G = conductance in Siemens (S) σ = conductivity in Siemens per meter (S/m) A = cross section area of conductor in meters squared (m2) L = conductor length in meters (m) P = power in Watts (W) α = temperature coefficient of resistance (K-1) θ = temperature in degrees Kelvin (K)