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Ohms Law Ohm's law is the most important, basic law of electricity. It defines the relationship between the three fundamental electrical quantities: current (I), voltage (V), and resistance (R).

Ohms Law The mathematical equation that shows the relationship between electric voltage, current and resistance. Ohms Law was named after Bavarian mathematician and physicist Georg Ohm.

Ohms Law When a voltage is applied to a circuit containing only resistive elements (i.e. no coils), current flows according to Ohm's Law. V=IR

Ohms Law Ohm's law states that the electrical current (I) flowing in an circuit is proportional to the voltage (V) and inversely proportional to the resistance (R).

Ohms Law In other words, if the voltage is increased, the current will increase provided the resistance of the circuit does not change.

Linearity of Voltage and Current for Resistors which Obey Ohms Law Voltage and current are linear when resistance is held constant.

Ohms Law Example: If the circuit has a 100 Ohm resistor and the voltage is increased from 12 Volts to 24 Volts, the current will increase. Likewise if the voltage is drop from 24V to 12V, the current will decrease.

Ohms Law Similarly, increasing the resistance of the circuit will lower the current flow if the voltage is not changed.

Ohms Law Example: If the circuit has a 12V supply and the resistance is increased from 100 Ohms 200 Ohms, the current will decrease. Likewise if the resistance is reduced from 200Ohms to 100Ohms, the current will increase.

Ohms Law The formula can be reorganized so that the relationship can easily be seen for all of the three variables.

Ohms Law Exercise: Verify Ohms Law by substituting values in each equation below. V = I x R R = V / I I = V / R

Ohms Law It should be evident that knowing any two of the values of a circuit, one can determine the third using Ohms Law. V = I x R R = V / I I = V / R

Ohms Law Another useful equation to know is the power equation: P = E*I (power equals voltage multiplied by current or watts = volts * amps).

Ohms Law From this we can substitute Ohm's law for any values we don't know. For instance if we need to know power but we only have amperage (I) and resistance (R) then we could substitute I*R in the power equation (because according to Ohm's law E=I*R) and get P = I*R*I.

Ohms Law Now that we have established a direct relationship with Power, Voltage, Current and Resistance, knowing any two of the values of a circuit, one can determine the third and fourth values using Ohms Law and the Power Formula.

Ohms Law This graphic is a good tool to use for solving any number of combinations of Ohms Law.

Experiment 1 One 10 ohm resistor connected to the battery. Connect a second 10Ω resistor in parallel to the first one Q:What will the new resistance be? What will happen to the current through each resistor and the voltage across each component of the circuit?

Conclusion V = I x R Ohms Law P = I x V Power Formula

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