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  Main Electricity Current & Potential Difference Lesson III.2.5 Electricity

Ohm's Law - Lesson III.2.5

Key Terms:

voltage |current | resistance | resistivity | superconductivity |IL, CCT, NUM

Georg Simon Ohm was a German physicist born in Erlangen, Bavaria, on March 16, 1787. As a high school teacher, Ohm started his research with the then recently invented electric cell, invented by Italian Conte Alessandro Volta. Using equipment of his own creation, Ohm determined that the current that flows through a wire is proportional to its cross sectional area and inversely proportional to its length. Using the results of his experiments, Georg 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. Unfortunately, when Ohm published his finding in 1827, his ideas were dismissed by his colleagues. Ohm was forced to resign from his high-school teaching position and he lived in poverty and shame. However, his research efforts gained allot of support outside of Germany. In 1849, Georg Simon Ohm was finally recognized for his efforts by being appointed as a professor at the University of Munich.
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 caused 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. Resistance Applet

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.

  • If we reorganize the variables of the equation we can solve for current (I) or resistance (R):

Name: Symbol: Units:
Voltage V volt(s)
Current I ampere(s) or amp(s)
Resistance Omega The Greek letter omega. ohm(s)

Ex 1: In electronics the resistor is a electrical component used to limit current. What size of voltage source is needed to produce 30 A through a 40 K resistor? Draw the schematic:

Ex 2: A common house hold resistor is a toaster. The toaster is plugged into the wall. Current flows from the voltage source (wall receptacle 120 V) into the toaster. The current encounters resistance in the toaster casuing light and heat to be emitted ultimately toasting the bread. C






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