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V = IR:  Say What?

                                                                                                                       February, 2014
Voltage, Current, Resistance -  Aaaagh!  Is this what you are feeling upon knowing that you have to teach these to your students, or learn about this if you want to build your own robot?

Well, no problem.  Once broken down a little, teaching or learning this fascinating aspect of science can be easy with a capital E. 

In order to completely understand voltage, current, and resistance (and their relationship), you need to recall those school and college lessons and remember the atom.  Atoms are the basic, most fundamental pieces of matter, which is anything that can be physically touched.  All matter contains atoms.  Each atom has tiny particles called protons (with a positive charge), neutrons (with no charge), and electrons (with a negative charge).  These positive and negative charges attract and stay together within the atom, so, when they are all together within an atom they are happy.  However, if they are separated, they want to get back together and will indeed exert any energy needed to get back to their happy place.  These positive and negative charges are needed to produce any type of electricity.  And…that is how the magic happens.

What is Voltage?

Well, let's begin with potential energy and potential difference. Potential energy is energy that is stored in an object, which has potential to do work.  The potential difference between two points, such as point A to point B is the amount of work that needs to be done to move it from point A to point B.  So, with that being said, voltage is electrical potential difference.  Electricity flows from point A to point B, and the amount of force that is used to flow between these two points is called the voltage.  The symbol for voltage is the capital “V” (and sometimes “E”), and the unit of measurement is called the volt (V). 

Think of a water tank, which usually stands high above ground.  It is high up for good reason:  to create pressure.  Pipes carry this water down and into your home because of the pressure from the water tank (that is high above ground) is pushing it down.  That is an example of voltage.  Thinking from an electrical standpoint, the voltage is pressure pushing on the electrons in a given circuit. 

What is Current?

Current is simply the flow of electric charge.  Those moving electrons, like in a wire?  When they move from one point to the next, well, that is current.  The symbol for current is the capital “I” and the unit of measurement is the amp (A). 

If you look outside and see power lines, that is one example of how current travels.  The electricity must travel from the power stations to homes and other buildings.  Another example of current (water current) is when you turn on your water faucet.  The water must travel through the pipes and then it will come out into your sink. 

What in the World is Resistance? 

Anything that keeps movement from happening, or brings something to a halt (and preventing it from moving any further) is resistance.  To me, of the three, Resistance can be the most confusing,  So allow me to explain, here are with a few examples. 

One example of resistance is air resistance.  If you are a parachutist, then air resistance is your friend.  This air resistance, obviously, slows down the speed of your descent.  Another example of resistance, and one that I  adults can probably relate to, is when you are moving furniture across the room.  The resistance (caused by friction, unless you have super slippery flooring) makes it a little difficult to move that heavy shelf from one side of the room to the other.  Now, of course with robots, we need to understand electrical resistance.  Electrical resistance slows down or even stops electrical current.  And when this happens, that built up energy turns into heat or light (and other stuff, which we'll talk about in one of our next articles).  The symbol for resistance is the capital “R” and the unit of measurement is the Ohm (Ω ).

And yes, they are one happy family!
Okay, now it's time to get technical.  All of these terms are related and thus work together.  There is a special name for this relationship between voltage, current, and resistance, and that name is Ohm's Law.  In 1826, a scientist by the name of George Ohm discovered this relationship.  He discovered that voltage and resistance, together, have an effect on the current flowing within a circuit. If there is an increase in voltage, then there the current will increase.  But, if there is an increase in resistance, then there will be a decrease in the current.  The actual law states that, and I quote, "a current flowing through a conductor is directly proportional to the voltage, given the temperature of the conductor remains constant".  This mathematical formula for Ohm's Law is
V = I x R.

When teaching the relationship between voltage, current, and resistance to students, we have found that using a lot of examples helps them grasp the concept.  Even if the stories or scenarios are not specifically about electricity, but are used to represent electricity, the students will have a deeper understanding of what could be a confusing concept.  (I wish my teachers would have incorporated stories into their lessons; I know this would have prevented a lot of frustration in those physical science courses!)