 Measuring current may be accomplished by using a meter called an Ammeter  This meter is placed in the path of the electron flow, and reads the flow in amperes.  The direction of the current moves from the positive side of the battery through the ammeter, the light, the toggle switch, and through the battery. (The letter "I" is the symbol for current.)

 The flow of electrons move from the negative terminal on the battery through to the positive terminal.  The Law of Electric Charge states the like charges repel and opposite charges attract. The excess of negative charges (electrons) on the negative terminal of the battery provide the 'push' force on the electrons.  At the same time the electrons feel a 'pull' towards the positive terminal of the battery (negative charge deficit). This push - pull effect moves the electrons through the path (conductors) of the circuit.

 The circuit above can be represented by a drawing called a schematic. A schematic replaces the pictures of the items such as the battery, switch, light, ammeter, and wires with symbols.  The symbol of the ammeter is  The symbol of the battery is  The symbol of the light is  The symbol of the switch is

  Schematic of the above circuit.

 George Simon Ohm was able to define the fundamental relationship between voltage, current, and resistance. These fundamental relationships are of such great importance, that they represent the true beginning of electrical circuit analysis.

 A relationship exists between current and voltage. When a load such as a light bulb is connected to a battery, the light turns on. The light glows because electrons are flowing through the tungsten filament.  The electrons bump into each other as well as the tungsten particles. When collisions take place friction is producing light and heat which is emitted from the light bulb.  The friction of the particles is called resistance. Resistance slows down current. Because the speed of electron flow is very fast when a resistor is placed in a circuit it will limit the amount of current flow in the circuit.

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 Ohm's law describes a mathematical relationship between three quantities. Voltage (V), Current (I) and Resistance (R) are related to each other through an equation.

Name:Symbol:Units: VoltageVvolt(s) CurrentIampere(s) or amp(s) ResistanceThe Greek letter omega. ohm(s)

1. Find the resistance of an electric bulb if a current of 0.80 A flows when the potential difference across the bulb is 120 V. R= 1.5 x What is the potential difference across a toaster of resistance 13.7 when the current flowing through is 8.75 A? V=120 V

 Resistance in Electric Circuits  #1-6