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Voltage, Current, and Resistance: Ohm’s Law

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Voltage, Current, and Resistance: Ohm’s Law

Physical Science

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Learners discover that when different voltages are applied to the same conductor, the ratio of voltage to current remains constant.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Explain that different conductors have different resistances to electricity.
  • Explain that when different voltage values are applied to the same conductor, the ratio of the voltage to the current remains constant.
  • Explain that for a conductor, the ratio of voltage to current is the resistance.

Everything You'll Have Covered

Before mankind understood or harnessed electricity, its effects were observed. Lightning has always been regarded as a powerful and fearful phenomenon, and cultures throughout history have recognized it as the calling card of deity or deity itself. Electricity was observed in places other than the sky, though. Ancient Egyptian texts from 2750 BC discussed electric fish and recorded that people received shocks from these creatures they called the "Thunder of the Nile." Author and Naturalist, Pliny the Elder, asserted in the first century AD that shocks could be administered by catfish and torpedo rays and that these shocks could travel along conducting objects. The ancient Greeks used amber in decoration and noticed that rubbing amber caused the attractive force that we now call static electricity.

Around 1600 AD, William Gilbert, physician to Queen Elizabeth I, studied electricity and magnetism and used the term elektron, Greek for amber, to coin the word electricity. After extensive research on electricity, in June 1752, Benjamin Franklin conducted his famous kite experiment. When Mr. Franklin flew his kite in the storm-charged sky, he observed the small fibers of the kite string standing on end and sparks jumping from the key to his hand and concluded that lightning must be electrical. Italian physicist Count Alessandro Volta developed the first electric cell in 1800. The SI derived unit of electromotive force, commonly called voltage, or potential difference is measured in volts (V) and is named after Count Volta. In the early 1800s, French physicist and mathematician, Andre-Marie Ampere, became one of the main discoverers of electromagnetism and laid the foundation for electrodynamics. The SI unit of measure for electric current, the ampere or amp for short (A), is named for him.

Georg Ohm, a German physicist and teacher, used Volta's recently invented electrochemical cell in his own research. Using equipment Ohm invented, he determined that the voltage across a conductor is proportional to the current passing through the conductor. The relationship Ohm defined between voltage, current, and resistance became known as Ohm's Law, and it applies to electrical circuits. The ohm (?) is the SI unit of electrical resistance. The mathematical equation that describes the relationship is V = IR, where V is the potential difference measured across the resistance in units of volts, I is the current through the resistance in units of amperes (A), and R is the resistance of the conductor in units of ohms (?). Ohm's Law is also stated mathematically as I = R/V or R = I/V.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts current, electrical circuits, voltage
Course Physical Science
Type of Tutorial Experiment
Key Vocabulary ammeter, conductor, current