__Electricity Tutorial 2 - Ohm’s 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 **Ohm’s 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**.

**ohmic** conductor.

What are the key points to Ohm’s Law? |

**Conductance** is the reciprocal
of resistance. It’s 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 doesn’t take a genius to see that:

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

And what is its conductance? |