Resistors and Ohms Law

Resistors are the most common component you will encounter in electronic circuits. A resistor resists the flow of electrons.

To understand this you first need to understand the concepts of voltage and current.

Electricity is the flow of electrons. Electronic circuits are all about controlling the flow of electrons in creative ways. A common analogy for think about the flow of electrons/electricity, is to imagine electrons flowing through wires as water flowing through a hose.

Imagine electricity is like water flowing through a hose. Current is how much water is flowing through the hose, and voltage is how fast the water is moving. So, current is like how much electricity is moving, and voltage is like how fast it’s moving through a wire.

So what is a resistor?

A resistor is a component with two legs. It’s job in a circuit is to impede the flow of electrons.

A resistor is like a tiny roadblock for electricity. It’s a component in an electrical circuit that limits how much current can flow through. It’s used to control or reduce the amount of electricity passing through a circuit. Resistors come in different sizes and types, and they’re often small and made of materials that resist the flow of electricity to varying degrees.

Resistors are measured in ohms. You might encounter values like:

• 100r = 100 ohms
• 1k = 1000 ohms
• 100k = 100,000 ohms
• 1M = 1,000,000 ohms (mega or million ohms)

What is ohms law?

Ohms law is a fundamental principle of electrical engineering! It describes how current flows and allows you to calculate the current, voltage, and resistance at any point in a circuit.

Ohm’s Law is like a rule that tells us how electricity works. It says that the current (how much electricity flows) in a wire is equal to the voltage (how fast electricity moves) divided by the resistance (how hard it is for electricity to move through something). So, if you know how fast electricity is moving (voltage) and how hard it is to move (resistance), you can figure out how much electricity is flowing (current) in a wire.

Some examples

Voltage dividers

A common circuit building block is called a voltage divider.

Imagine you have a highway where cars are like electricity flowing through wires. Now, think of a voltage divider as a special exit ramp on the highway. When a car takes this exit, it splits off from the main highway into two smaller roads. Similarly, in electronics, a voltage divider splits a higher voltage into two smaller voltages using resistors. Just like cars choose different roads at an exit, electricity “chooses” different paths through resistors to create the right voltage levels needed in a circuit.

Look at the first example. 9 volts are going through R1 and R2. What is the voltage at the intersection ?1. You can solve this if you understand voltage dividers. The formula is: 

• ?1 = 9V * (R2 / (R1 + R2))
• ?1 = 9V * (1K / (1K + 1K))
• ?1 = 9V * 1000 / (1000 + 1000)
• ?1 = 9V * 1000 / 2000
• 4.5V = 9V * 0.5

Here I walked through the steps to solve the problem. Notice I converted 1K to 1000 ohms. Then finished up from there. 

The formula is: V * R2 / (R1 + R2)

The shortcut when both resistors are the same value, the voltage is divided in half. This is true for any value for R1 and R2. Try it yourself. Imagine R1 and R2 are 10K. Then try R1 and R2 at 47K and 100K.

What happens when the values are not equal? What’s the voltage at the intersection: ?2. 

• ?2 = 9V * 100K / (100K + 20K)
• ?2 = 9V * 20K / 120K
• ?2 = 9V * 20,000 / 120,000
• 1.5V = 9V * 0.166

Solve number 3 on your own!

To solve ?4 we have to know that resistors in series are added together. That means that we have a total resistance of 16.7K. To solve ?4:

• ?4 = 9V * (10K + 4.7K) / (2K + 4.7K + 10K)
• ?4 = 9V * 14.7K / 16.7K
• ?4 = 9V * 0.88
• ?4 = 7.92

Solve ?5 on your own…

With this knowledge you can start examining the Rangemaster circuit. Notice R1and R2 for a voltage divider! Calculate the voltage at the intersection of R1 and R2.