The two electrical formulas, Ohm’s Law and Watt’s Law, are fundamental in the basic understanding of electricity. Useful in a variety of situations in order to determine how much current, volts, or watts an electrical system is using.

**Power (P)** is measured in *watts*. **Voltage (V)** is measured in *volts*. **Current (I)** is measured in *amps*. **Resistance** (R) is measured in *ohms*.

Voltage can be thought of as electrical pressure.

**Ohm’s Law**

Ohm’s law is named after Georg Simon Ohm (a German physicist)

The following are the three formulas used for Ohm’s Law:

Voltage (V) = Current (I) x Resistance (R)

Current (I) = Voltage (V) / Resistance (R)

Resistance (R) = Voltage (V) / Current (I)

*Example 1:*

*Example 2:*

*Example 3:*

**Watt’s Law**

The watt is a unit of power that is named after James Watt (an 18th-century Scottish inventor, mechanical engineer, and chemist).

The following are important formulas to remember:

Power (P) = Voltage (V) x Current (I)

Current (I) = Power (P) / Voltage (V)

Voltage (V) = Power (P) / Current (I)

*Example 1:*

*If a 120 Watt light bulb is rated to use 120 Volts of power, how much current would the light bulb draw?
*Click to Reveal the Answer: 1 Amp

*Example 2:
If a 3 Watt submersible water pump is rated to use 5 Volts of USB power, how much current would the water pump draw?
*Click to Reveal the Answer: 0.6 Amps

*Example 3:
*

*If a 3 Watt aquarium filter is rated to use 110 Volts of power, how much current would the aquarium filter draw?*

Click to Reveal the Answer: 0.027 Amps