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Physics: Electric Current and Related Equations

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  • What letter represents electric current?
    Electric current is represented by the letter I.
  • What is the SI unit of electric current?
    The SI unit of electric current is the ampere (A).
  • What letter represents current density?
    Current density is represented by the letter J.
  • What is the SI unit of current density?
    Current density is measured in coulombs per second per square meter (C/s·m²) or amperes per square meter (A/m²).
  • What letter represents conductivity?
    Conductivity is represented by the Greek letter σ (sigma).
  • What is the SI unit of conductivity?
    Conductivity is measured in 1/(ohm·meter) or S/m.
  • What letter represents resistivity?
    Resistivity is represented by the Greek letter ρ (rho).
  • What is the SI unit of resistivity?
    Resistivity is measured in ohm·meter (Ω·m).
  • What letter represents resistance?
    Resistance is represented by the letter R.
  • What is the SI unit of resistance?
    Resistance is measured in ohms (Ω).
  • Equation relating drift velocity \(v_d\) to electric field \(E\)
    \(v_d = q \tau_m E\) where q is charge and τm is mean free time.
  • Equation relating current density \(J\) to drift velocity \(v_d\)
    \(J = nqv_d\) where n is charge carrier density and q is charge.
  • Equation relating current density \(J\) to conductivity \(\sigma\) and electric field \(E\)
    \(J = \sigma E\)
  • Equation relating current density \(J\) to resistivity \(\rho\) and electric field \(E\)
    \(J = \frac{1}{\rho} E\)
  • Equation relating current \(I\) to current density \(J\) and cross-sectional area \(A\)
    \(I = J \cdot A\)
  • Equation relating current \(I\) to charge \(Q\) and time \(t\)
    \(I = \frac{dQ}{dt}\)
  • Equation defining resistance \(R\) of a wire based on resistivity \(\rho\), length \(L\), and cross-sectional area \(A\)
    \(R = \rho \frac{L}{A}\)
  • Ohm's Law equation relating voltage \(V\), current \(I\), and resistance \(R\)
    \(V = RI\)
  • Power formulas for a circuit element

    Power can be calculated as \(P = VI\), \(P = RI^2\), or \(P = \frac{V^2}{R}\).

  • Equation relating battery terminal voltage \(V_{ab}\), emf \(E\), current \(I\), and internal resistance \(r\)
    \(V_{ab} = E - Ir\)