What makes a circuit?

Any circuit has two things, a potential difference, also called the voltage, and a resistor that connects the high end of the voltage to the low end 

Potential difference (Voltage)

   The voltage "pushes" charges in a circuit.  Voltage has also been referred to Electrostatic pressure because a simple circuit is often explained by using plumbing. In the plumbing example the voltage is a pump that draws water up and pushes it through the pipes. 

   What the voltages does is give every charge in a circuit energy.  The charges then want to move to a lower energy state.  Think of this like gravitational energy, you lift an object up giving it high gravitational energy.  Letting it go, the object wants to give up it's potential energy and falls.  The charge in a circuit is like that mass held high, then let go.  

   The scienitific definition of voltage is 1 volt is enough electrostatic potential to push 1 coloumb of charge per sec through a 1 ohm resistor. 


    A resistor is anything that slows or stops the flow of current from moving from a high potential to a low potential.  Simply enough a resistor resist the flow current. 

    What effects resistance? There are some geometry factors that we will talk about later.  Their are a few things about the material that also effect the resistance. The first thing is the amount of free electrons per volume.  The other thing that effects the resistance is the amount a collisions the charge experience as it moves from one point to another. 

    These two features what makes up resistivity.  Every material has it's own resistivity, and that resistivity can change with temperature on humidity. 

     Every substance, with the exception of superconductors, have a resistance. Metals, like copper and gold have; conductors, have low resistance.  Glass, wood, and plastics have very high resistance are insulators.  

Symbols of Circuits

Connection Lead 

Battery of Cell 



Power Supply 

This is the universal symbol for resistors, the truth is every piece of wire is a resistor but we consider them to be resistance-less.  The symbol IB uses for resistors is a rectangle 


 This is the universal symbol for a voltage.  The larger of the two plates is the positive (or higher positive end).  From the diagram positive charge flows from larger plate, travels the circuit and returns to negative end.  The truth is the exact opposite happens a negative charge leaves the negative direction, moves in the opposite direction of the current to the positive end.