Ohms Law

Overview

Ohms law describes an important relationship between voltage, current and resistance. Current is rate of flow of electrons which make your circuits work. Voltage represents a pressure moving current forward. Resistance represents an opposing pressure limiting the flow of current. In a wire you can imagine, voltage pushing current forward and resistance pushing current back. The total flow or current is proportional to the voltage and inversly proportional to the resistance. This relationship is called Ohms law and is represented as follows.

V/R = I

V represents voltage. R respresents resistance and I represents current. The I comes from the French for current. It also important that the units of measurement for Ohm’s law are Volts for voltage, Ohms for resistance and Amps for current. In this class we normally talk about Ohms law in the following format.

V = IR.

Exercise

Using Ohm’s law you can easily calculate voltage, resistance or current given any two of the three. Calculate the missing values in the table below. Copy and complete the following table in your notebook. Noee that the last row contains the units milliamps, so you wil need to convert this unit to amps before using Ohms law. Please round any fractions to the nearest thousandth.

Ohms Law

Circuit

Voltage

Current

Resistance

1

5.00 Volts

100 Ohms

2

3.00 Volts

.020 Amps

3

.005 Amps

330 Ohms

4

12.00 Volts

.400 Amps

5

1.80 Volts

470 Ohms

6

.250 Amps

1000 Ohms

7

30 milliamps

330 Ohms