Ohm’s Law

Understanding Voltage, Current, Resistance, and Power in Electrical Circuits

What is Ohm’s Law?

Ohm’s Law describes the relationship between voltage, current, and resistance in an electrical circuit.

The fundamental equation is:

::contentReference[oaicite:0]{index=0}

If any two values are known, the third can be calculated.

<--Calculator-->

/* Hide browser number input spinners */ #olc-wrap input[type=”number”]::-webkit-inner-spin-button, #olc-wrap input[type=”number”]::-webkit-outer-spin-button { -webkit-appearance: none; margin: 0; } #olc-wrap input[type=”number”] { -moz-appearance: textfield; }

Voltage (V)

Resistance (R)

Current (I)

Power (P)

Enter any 2 values to solve for the others

Electrical Quantities

Quantity	Symbol	Unit
Voltage	V	Volts (V)
Current	I	Amperes (A)
Resistance	R	Ohms (Ω)
Power	P	Watts (W)

Ohm’s Law Formulas

Find	Formula
Voltage	V = I × R
Current	I = V / R
Resistance	R = V / I
Power	P = V × I
Power	P = I²R
Power	P = V²/R

Example 1: Finding Current

Given:

Voltage = 12 V

Resistance = 4 Ω

Use:

I = V / R

I = 12 / 4

Current = 3 A

Example 2: Finding Voltage

Given:

Current = 5 A

Resistance = 10 Ω

Use:

V = I × R

V = 5 × 10

Voltage = 50 V

Example 3: Finding Resistance

Given:

Voltage = 24 V

Current = 6 A

Use:

R = V / I

R = 24 / 6

Resistance = 4 Ω

Example 4: Finding Power

Given:

Voltage = 120 V

Current = 2 A

Use:

P = V × I

P = 120 × 2

Power = 240 W

Ohm’s Law Wheel

Variable	Formulas
Voltage (V)	IR, √(PR), P/I
Current (I)	V/R, P/V, √(P/R)
Resistance (R)	V/I, V²/P, P/I²
Power (P)	VI, I²R, V²/R

Practice Problems

Problem 1

A 9 V battery is connected to a 3 Ω resistor.

Show Answer

I = V/R = 9/3 = 3 A

Problem 2

A current of 2 A flows through a 15 Ω resistor.

Show Answer

V = IR = 2 × 15 = 30 V

Problem 3

A device uses 120 V and draws 5 A.

Show Answer

P = VI = 120 × 5 = 600 W

Challenge Problem

A 240 W heater operates on 120 V.

Show Answer

I = P/V = 240/120 = 2 A
R = V/I = 120/2 = 60 Ω