Introduction to Ohm's Law

Objective:

At the end of this module, you will be able to calculate the relationship between resistance, voltage and current using Ohm's Law.

References:

Textbook: DC/AC Principles: Analysis and Troubleshooting - Chapter 3 Ohm's Law

Theory:

Ohm's Law provides a simple mathematical relationship between Resistance, Current and Voltage.

The relationship is expressed as:

V = I x R

Where:

• V = Voltage in units of Volts (Symbol V)
• I = Current in units of Amperes ( Symbol A)
• R = Resistance in units of Ohms (Greek Symbol Omega)

Example

A Series Circuit has a current I = 10 mA flowing through a resistor R1 = 5 Kohm. What is the voltage of the Voltage Source Vs ?

Using Ohm's Law:

V = I x R

We can substitute the values for the current I and the resistance R1 in the above equation.

V = 10 mA x 5 Kohms = 50 Volts

Self-Test

1. True or False

Ohm's Law provides a simple mathematical relationship between Voltage, Current and Resistance in an electric circuit.

2. Ohm's Law states that:

• a. current is inversely proportional to the voltage and directly proportional to the resistance.
• b. current is directly proportional to the voltage and inversely proportional to the resistance.
• c.current is directly proportional to the voltage and directly proportional to the resistance.
• d.current is inversely proportional to the voltage and inversely proportional to the resistance.

3. What would be the effect on the current flowing through a resistor if the resistance increased while the voltage remained constant?

• a. current would increase.
• b. current would increase exponentially.
• c. current would decrease.
• d. current would remain constant.

4. If the applied voltage Vs is 85 Volts and R1 = 9 Kohm, solve for the circuit current:

• a. 15.0 mA
• b. 765 KA
• c. 9.44 mA
• d. 106 A

When you are ready to take the module test click here.