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How to Calculate Amperes From Wire Speed

Electricity is created to the flow of electrical current through metallic wires. The electrical current consists of many millions of electrons traveling at high speeds. Electrical current is actually a scaled version of electron velocity. The electrical current flowing through a wire (in units of Amperes) can be calculated from a few simple quantities such as electron charge, cross-sectional area of wire, and number of electrons. The calculation is a common problem within college physics.

Things You'll Need

Calculator
Calipers

Instructions

- 1
  Write down the equation for electrical current. The equation states:
  
  I = n q v A
  
  I is the current, n is the number of electrons, q is the charge of an electron, v is the electron velocity and A is the cross-sectional area of the wire.
- 2
  Measure the diameter of the wire using the calipers. Assuming the wire is circular, the cross-sectional area of the wire is:
  
  A = 3.14 x (0.5 x d)^2
  
  d is the diameter of the wire.
- 3
  Calculate the Amperes using the equation for current:
  
  I = n q v A
  
  The charge of an electron is 1.6 x 10^-19 Coulomb's, the cross-sectional area was measured, the velocity of the electrons and number of electrons should be given in the question. If the quantities are not given in the question assume the velocity to be the Fermi velocity (0.00028 meters/second for copper), and the number of electrons to be approximately 8.5 x 10^28 electrons per cubic meter (true for copper).

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