Ohm's Law - Voltage, Current and Resistance

ohm's law equation

Ohmís law formulas are used around the world to determine electromotive force.

Ohm’s law is the fundamental equation that explains the relationship between voltage, current and resistance in a circuit. The power dissipated in a load resistance(R) is defined as the product of the electric current and applied voltage (P=VI). By substitution other relationships of power can be derived by applying ohms law.

Before describing ohm’s law, let’s define the three main parameters that are fundamental to any electric circuit.

Voltage: Also known as a Electric Potential Difference, is a driving force in any circuit; it is measured in Volts (V).

Current: Is the flow of electrons from a higher potential to a lower potential, its unit is Ampere (A)

                   There must be a closed loop or path for the existence of current flow

Resistance: Is the characteristic of a medium that opposes the flow of current. The unit of resistance is      

                      Ohms & it is represented by the Greek letter Ω (Omega).

 

Georg Ohm     

Georg Simon Ohm, the inventor of Ohm's Law, was born in Erlangen, Bavaria, on March 16, 1787.His Father, a successful mechanic, wanted him to study science however Ohm became a high school teacher. Ohm had aspirations to join university, but at that time the only way to join university was providing important invention through scientific research. Since the science of electricity was at the infancy stage ohm decided to study the behavior of current in resistive circuits. Since equipment was technically unaffordable for ohm, he made much of his own. Ohm determined experimentally that the amount of electricity in terms of current that flows along a wire in an electrical device was directly proportional to its cross sectional area and inversely proportional to its length from this results ohms was able to define resistance and show that there is a simple relationship proportioanl to the voltage, resistance and current.; this result now known as the ohms law; the most fundamental relationship in circuit theory. However when published in 1827 ohms results were met with ridicule as a result not only did ohm miss out on a university appointment he was also forced to resign from his high school teaching position. While ohm was living in a poverty and shame, his work on dc circuits became known and appreciated outside Germany .In 1852; Ohm was appointed a member of the Royal Society. Finally, in 1849, he was appointed as a professor at the University of Munich, where he was at last recognized for his important contributions.

 

According to Ohm, he determined experimentally that current in a resistive circuit is directly proportional to its applied voltage and inversely proportional to its resistance. This is what is known as Ohm's Law.

In equation form, Ohm’s law states the current (I) that flows through the Resistor(R) is:

                                                          I=E/R   [amps, A]

                                              Where   E is applied voltage in volts

                                                             R is the resistance in ohms  

                                                             I is the current in amperes

From the above formula for we can see that as the applied voltage increases the current also increases, as the resistance increases the current decreases.

 


Fig. 1a

 



Fig. 1b

 



Fig. 2

 

To conduct this Ohm's Law experiment:

  1. First, connect a battery/source in series with an Ammeter and a fixed value Resistor
  2. Then, connect a voltmeter in parallel as shown in Fig. 2. Then, Record the current, voltage and resistance values.
  3. Then, disconnect the batter and replace the resistor with a higher value one. Record the values of current for different value of Resistors.
  4. Finally, Observe how the current varies for different values of resistors.

 

For a fixed resistance doubling the voltage doubles the current measured, while tripling the voltage triples the current. For a fixed voltage, doubling the resistance halves the current, while tripling the resistance reduces the current to 1/3 of its original value and so on.

 


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