Electricity Tutorial 2 - Ohmís Law

Resistance is the opposition to the flow of an electric current.  Resistance in a conductor is thought to arise due to the collisions between the charge carriers and the ions in the lattice.  The internal energy rises, so the conductor gets hot.  The hotter the conductor, the greater the probability of a collision between an ion and an electron.  The resistance in hot conductors rises.

Resistance is also the ratio of the voltage to the current, described in the simple equation R = V/I.  In a metallic conductor, we find that if we alter the voltage or the current, the other variable changes in such a way that the ratio remains constant. 

R = V 

      I

 

This is Ohmís Law, which states:

The current in a metallic conductor is directly proportional to the potential difference between its ends provided that the temperature and other physical conditions are the same.

  A conductor that obeys Ohmís Law is called an ohmic conductor.

Question 1 

What are the key points to Ohmís Law?

Answer

Conductance is the reciprocal of resistance.  Itís a term often used by electrical engineers in preference to resistance.  Conductance is given the physics code G and the units Siemens (S).  It is related to resistance by the equation:

 

So it doesnít take a genius to see that:

 

Question 2

A component takes a current of 0.35 A from a 12 V supply.  What is the resistance of the component?

Answer

Question 3

And what is its conductance?

Answer