The mathematical relationship between voltage, current, and resistance was discovered in 1826 by Georg Simon Ohm. The relationship, known as Ohm’s law, is the basic foundation for all circuit analysis in electronics. Ohm’s law, which is the basis of this chapter, states that the amount of current, I , is directly proportional to the voltage, V , and inversely proportional to the resistance, R .

Expressed mathematically, Ohm’s law is stated as I=R/V

What you are expected to learn

At the end of this module, you should be able to:

• Identify the three basic parts of a circuit.

• Identify three types of circuit configurations.

• Describe how current flow can be varied in a circuit.

• State Ohm’s law with reference to current, voltage, and resistance.

• Solve problems using Ohm’s law for current, resistance, or voltage in series, parallel, and series-parallel circuits.

• Describe how the total current flow differs between series and parallel circuits.

• Describe how the total voltage drop differs between series and parallel circuits.

• Describe how the total resistance differs between series and parallel circuits.

• State and apply Kirchhoff’s current and voltage laws.

• Verify answers using Ohm’s law with Kirchhoff’s law.

How to learn from this module

Going through this module can be both a fun and a meaningful learning experience. All you need to do is make use of your time and resources efficiently. To do this, here are some tips for you:

1. Take time in reading and understanding each lesson. It is better to be slow but sure than to hurry finishing the module only to find out that you missed the concepts you are supposed to learn.

2. Do not jump from one chapter to another. Usually, the lessons are arranged such that one is built upon another, hence an understanding of the first is essential in comprehending the succeeding lessons.

3. Be honest. When answering the test items, do not turn to the key to correction page unless you are done. Likewise, when performing experiments, record only what you have really observed.

4. Safety first. Perform the experiments with extra precaution. Wear safety gears whenever necessary.

5. Don’t hesitate to ask. If you need to clarify something, approach your teacher or any knowledgeable person.

What to do before (Pretest)

Lesson 6: Ohm's Law

Ohm’s law defines the relationship among three fundamental quantities: current, voltage, and resistance. It states that current is directly proportional to voltage and inversely proportional to resistance.

Three formulas denote this law:

E = IR

I = E/R

R = E/I

•An electric circuit consists of a voltage source, a load, and a conductor.

• The current path in an electric circuit can be series, parallel, or series-parallel.

• A series circuit offers only one path for current to flow.

• A parallel circuit offers several paths for the flow of current.

• A series-parallel circuit provides a combination of series and parallel paths for the flow of current.

• Current flows from the negative side of the voltage source through the load to the positive side of the voltage source.

• Current flow in an electric circuit can be varied by changing either the voltage or the resistance.

• The relationship of current, voltage, and resistance is given by Ohm’s law.

• Ohm’s law states that the current in an electric circuit is directly proportional to the voltage applied and inversely proportional to the resistance in the circuit.

• Ohm’s law applies to all series, parallel, and series-parallel circuits.

Ohm Law Simulation Activity

Ohm's Law Practice Problems

• To determine unknown quantities in a circuit:

— Draw a schematic of the circuit and label all quantities.

— Solve for equivalent circuits and redraw the circuit.

— Solve for all unknown quantities.

• Kirchhoff’s current law: The algebraic sum of all the currents entering and leaving a junction is equal to zero; it may be restated as the total current flowing into a junction is equal to the sum of the current flowing out of that junction.

• Kirchhoff’s voltage law: The algebraic sum of all the voltages around a closed circuit equals zero; it may be restated as the sum of all the voltage drops in a closed circuit will equal the voltage source.

Kirchhoff's Law Simulation Activities

Kirchhoff's Voltage Law (KVL) | 2 bulbs (#1)

Kirchhoff's Voltage Law (KVL) | 2 bulbs (#2)

Kirchhoff's Voltage Law Practice Problem

Kirchhoff's Current Law Practice Problems

Kirchhoff's Voltage Law (KVL) | 2 bulbs + regulated DC power supply

Kirchhoff's VOLTAGE Law (KVL) | 1 bulb + 1 resistor

Kirchhoff's CURRENT Law (KCL) | 1 bulb + 1 resistor

Kirchhoff's CURRENT Law (KCL) | 2 bulbs

Ohm's Law Virtual Laboratory

Important Terms

• Ampere the basic unit of current.

• Electron volt (eV) a small unit of work or energy that represents the amount of work required to move a single electron between two points having a potential difference of 1 volt.

• Horsepower (hp) a unit of mechanical power corresponding to 550 ft·lb/s. In terms of electric power, 1 hp= 746 W.

• Inverse relation a relation in which the quotient of a fraction decreases as the value in the denominator increases with the numerator constant. In the equation I =V/R , I and R are inversely related because I decreases as R increases with V constant.

• Joule a practical unit of work or energy.

• Kilowatt-hour (kWh) a large unit of electrical energy corresponding to 1 kW = 1 h.

• Linear proportion a relation between two quantities which shows how equal changes in one quantity produce equal changes in the other. In the equation I =V/R , I and V are directly proportional because equal changes in V produce equal changes in I with R constant.

• Linear resistance a resistance with a constant value of ohms.

• Maximum working voltage rating the maximum allowable voltage that a resistor can safely withstand without internal arcing.

• Nonlinear resistance a resistance whose value changes as a result of current producing power dissipation and heat in the resistance.

• Ohm the basic unit of resistance.

• Open circuit a broken or incomplete current path with infinitely high resistance.

• Power the time rate of doing work.

• Short circuit a very low resistance path around or across a component such as a resistor. A short circuit with very low R can have excessively high current.

• Volt the basic unit of potential difference or voltage.

• Volt ampere characteristic a graph showing how much current a resistor allows for different voltages.

• Watt the basic unit of electric power.