Ordinary matter is made up of atoms that have positively charged nuclei and negatively charged electrons surrounding the nucleus. There is NO significance to the circles used to represent the proton and electron. The circles do NOT imply size or shape. Electrons and protons have a property called "charge" which is the same size but opposite in polarity (i.e., proton is + and electron is -). The proton has 1836X the mass of the electron BUT exactly the same size charge. The idea of charge suggests the proton and electron will strongly attract each other. Like charges (two protons or two electrons) strongly repel each other. "Like charges repel and unlike charges attract".

The rate of flow of electric charge is called ELECTRIC CURRENT. Current is measured in amperes. The conventional current direction is from high voltage to low voltage. Thus electric current is from a high energy source to low energy source. When a conductor is attached to a battery, as shown in the diagram, the electrons (blue) begin an orderly flow towards the battery’s positive terminal to create an electric current. Note: In this diagram, the current flows (…or moves…) from the positive terminal (right) to the negative terminal (left).

OK…The flow of charge (…or charge in motion…) is called CURRENT. In science terminology, current is the rate at which electric charges pass though a conductor. NOTE: The charged particle can be either positive or negative. RECALL – Current is identified as I and the unit of measurement is amps (A). To worry you, amps = coulombs / sec, a coulomb is a measure of electrical charge AND the rate of flow of electrical charge is current

So…what makes current (i.e., the flowing charge)? For a a charge to flow, it needs a push (a force). The force is supplied by VOLTAGE…also called the Potential Difference. Since charge flows from high to low, it makes sense that the charge flows from high potential energy difference to a low potential energy difference.

An example… Battery A has a potential of 12 V and Battery B has a potential of 2 V. Thus, there is a Potential Difference. That is, A has higher potential energy than B. This potential difference means there is voltage. In this case, the potential difference is V A – V B = = 10

So…we now know that if a potential difference occurs between two regions AND the regions are joined together, the charge will flow. Will charge continually flow? If the two regions are joined, the charge will move until… (1) the force acting on it is reduced to a minimum (i.e., the push cannot move the charge) OR (2) the voltage becomes the same (i.e., Potential Difference is zero).

OK… Now…What if Battery C and Battery D each have a potential of 7 V. Is there voltage and current? There is no Potential Difference. Why? The Potential Difference is: V C – V D = = 0 Therefore, it has no voltage, AND it means no flow of charge.

Going on, we know that… Current (I) measures the amount of charge that passes a given point every second. The unit for current is ampere (A). Let’s add more… Charge (Q) is the unit of electric charge. It is measured in coulombs (C). Put together…. One amp (A) means that one coulomb (C) of charge passes a point in the electric circuit every second.

Circuits require the correct amount of voltage AND current to work. To measure current, a current-measuring device called an AMMETER must be inserted into the circuit so that the current can flow through it. The ammeter is measuring the flow of electric current in a circuit. A VOLTMETER measures the voltage difference between two points in an electric circuit.

So…we have a current flow and voltage. How does our light bulb work? We need RESISTANCE…or opposition to the flow of electric current. The unit of resistance is ohm and the symbol is Ω. Resistance varies in different materials. Gold, silver and copper have low resistance (i.e., current can flow easily through these materials). Glass, plastics and wood have very high resistance (i.e., current can not pass through these materials easily).

Now the light bulb… We have current (I), voltage (V), and finally, resistance (R). R is the wire inside the light bulb. The electric current flows through the wire in the light bulb. The wire is a resistor…so it prevents or limits the flow. This excites the electrons that are the current. The product of the excitement is heat and energy. The wire becomes hot, and gives off heat and light energy. Why doesn’t the wire burn? The wire is sealed in a glass bulb. There is no oxygen in the bulb. Without oxygen, there is no combustion.

The relationship between current, voltage and resistance is known as Ohm's law. The Ohm’s law suggests that there is a proportional relationship between current, voltage and resistance. Confusing…let’s talk it through… Let’s say current is constant but resistance changes. Under Ohm’s law, voltage will change is proportion to the change in resistance. That is, voltage will double if resistance doubles. If resistance is lowered by 25%, the proportional change in voltage is also a 25% decrease.

The scientific formula is… V = I x R That is Voltage = Current X Resistance. Well done…you have learned the first part of electricity.

I get it…. The flow of _______________________________ is called the current and it is the rate at which electric charges pass though a conductor. The _________________________ measures the amount of charge that passes a given point in each second. What is the resistance of a circuit if voltage is 3 V and current is 2 A. ____________________ ohm. What is the current of a circuit if resistance is 3 ohm and voltage is 15V? ____________________ A What is the voltage of a circuit if resistance is 7 ohm and current is 0.5 A? ____________________ V