Ohm's Law

Ohm's Law is a scientific principle that explains the relationship of voltage, resistance and current in an electrical circuit. Ohm's Law states that the current (amount of electrons flowing) is equal to the voltage divided by the resistance in the circuit. Stated another way, voltage is equal to the current times the resistance. Ohm's Law can also be used to calculate the resistance in the circuit. Resistance is equal to the voltage divided by the current. Ohm's Law shows that current is directly proportional to voltage and inversely proportional to resistance. Knowledge of Ohm's Law allow us to design new electrical circuits and understand how electricity flows in existing circuits.

Voltage - electrical force that moves electrons through a conductor. Voltage is electrical pressure also known as EMF (Electro Motive Force) that pushes electrons.

The greater the difference in electrical potential push (difference between positive and negative), the greater the voltage force potential.

Voltage is an electromotive force or potential difference expressed in volts.

Resistance - Resistance is the force opposing voltage, it resists movement of electrons

Higher resistance will decrease the flow of electrons and lower resistance will allow more electrons.

Current - the quantity or flow rate of electrons moving past a point within one second. Current flow is known as amperage, or amps for short.

Higher voltage will produce a higher current flow, and a lower voltage will produce a lower current flow.

Ohm's Law Equations

V = Voltage I = Current R = Resistance

V = I x R or I = V/R or R = V/I

V = I x R

Voltage equals current times resistance

I = V/R

Current equals voltage divided by resistance.

R = V/I

Resistance equals voltage divided by current.

Examples

#1 A circuit has a battery providing six volts and a load that is providing twelve ohms of resistance. How much current is flowing through the circuit?

Step 1: List the Given Information

V = 6 volts

R = 12 ohms

I = ?

Step 2: Equation

I = V / R

Step 3: Substitution

I = 6 / 12

Step 4: Solve the Equation for the Unknown

I = 6 / 12 = 3 / 6 = 1 / 2

I = .5

Step 5: State the Solution

I = .5 amps

#2 A circuit has a source that provides one hundred ten volts and a load providing two thousand two hundred ohms of resistance. How much current is flowing through the circuit?

Step 1: List the Given Information

V = 110 volts

R = 2200 ohms

I = ?

Step 2: Equation

I = V / R

Step 3: Substitution

I = 110 / 2200

Step 4: Solve the Equation for the Unknown

I = 110 / 2200 = 11 / 220 = 1 / 20

I = .05

Step 5: State the Solution

I = .05 amps

#3 A circuit has a battery that provides eighteen volts and a load providing three ohms of resistance. How much current is flowing through the circuit?

Step 1: List the Given Information

V = 18 volts

R = 3 ohms

I = ?

Step 2: Equation

I = V / R

Step 3: Substitution

I = 18 / 3

Step 4: Solve the Equation for the Unknown

I = 18 / 3 = 6 / 1

I = 6

Step 5: State the Solution

I = 6 amps

#4 A circuit has a battery that is providing an unknown amount voltage. A light bulb in the circuit has twenty ohms of resistance and the current has been measured at one half amp. How much voltage is the battery providing?

Step 1: List the Given Information

R = 20 ohms

I = .5 amps

V = ?

Step 2: Equation

V = I x R

Step 3: Substitution

V = .5 x 20

Step 4: Solve the Equation for the Unknown

V = .5 x 20

V = 10

Step 5: State the Solution

V = 10 volts

#5 A circuit has a battery that is providing twenty four volts and a load the is providing an unknown amount of resistance. Five hundredths of one amp is measured flowing through the circuit. How much resistance is in the circuit?

Step 1: List the Given Information

I = .05 amps

V = 24 volts

R = ?

Step 2: Equation

R = V / I

Step 3: Substitution

R = 24 / .05

Step 4: Solve the Equation for the Unknown

R = 24 / .05 = 2400 / 5

R = 480

Step 5: State the Solution

R = 480 ohms

Tools for Measuring Electricity

Volt-Meter

Amp-Meter

Multi-Meter

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