Basic Laws

Another week has passed and our journey is still on its surface making some preparations to plunge into the depths of the circuits world. One must be fully prepared, body and soul, for a long journey.

Those individuals who, in our thoughts, only exist in the books are the reasons we live with much comfort. Can anyone imagine life without electricity? Nah, seven days without electricity makes one weak. So, settle down guys and join me in our second week in electric circuits. :)

After being introduced to the basic concepts such as current, voltage, and power in an electric circuit, we are ready to determine the values of these variables provided we understand some fundamental laws known as the Ohm's law and Kirchhoff's law. Wait, wait, wait. Ohm? Kirchhoff? Who are these people? How come they have their own law? Can I have my own law, too? Come on buddy, introduce them first.

Georg Simon Ohm was a German physicist and mathematician. As a school teacher, Ohm began his research with the new electrochemical cell, invented by Italian scientist Alessandro Volta. Using equipment of his own creation, Ohm found that there is a direct proportionality between the potential difference (voltage) applied across a conductor and the resultant electric current. This relationship is known as Ohm's law.

On the other hand, Gustav Robert Kirchhoff was a German physicist who contributed to the fundamental understanding of electrical circuits, spectroscopy, and the emission of black-body radiation by heated objects. He coined the term "black body" radiation in 1862, and two different sets of concepts (one in circuit theory, and one in thermodynamics) are named "Kirchhoff's laws" after him; there is also a Kirchhoff's Law in thermochemistry. The Bunsen–Kirchhoff Award for spectroscopy is named after him and his colleague, Robert Bunsen.

Well, enough for them. What exactly is their law about that made them important in the field of physics?

Ohm's law is made from 3 mathematical equations that shows the relationship between electric voltage, current and resistance. It can be stated in mathematical equations all derived from the same principle.

In the following equations,

V is voltage measured in volts,
I is current measured in amperes and
R is resistance measured in ohms

V = I x R  (Voltage = Current multiplied by Resistance)

R = V / I  (Resistance = Voltage divided by Current)

I = V / R  (Current = Voltage divided by Resistance)



Sometimes it's very helpful to associate these formulas visually. The Ohms Law "wheels" can be a very useful tool to jog your memory and help you to understand their relationship.

The wheel above is divided into three sections:
Volts V (on top of the dividing line)
Amps (amperes) I (lower left below the dividing line)
Resistance R (lower right below the dividing line)
X represents the (multiply by sign)


To use, just cover the unknown quantity and what is left is the formula to find the unknown.


Example:

To find the current of a circuit (I), just cover the I or Amps section and what remains is the V volts above the dividing line and the R ohms (resistance) below it. Now substitute the known values. Just divided the known volts by the known resistance.
Your answer will be the current in the circuit.
The same procedure is used to find the volts or resistance of a circuit!
 

This video below will help you understand further Ohm's law.

Missing something? Of course, there is. We haven't discussed about Kirchhoff yet. So, be sure to visit again next week, okay? 'Till next time, then! Bye-bye and GOD bless!