Ohms Law Explained - The basics circuit theory

Summary

In this video from theengineeringmindset.com, Paul explains Ohm's Law, detailing its relationship between voltage, current, and resistance. He introduces Ohm's triangle (V-I-R) to simplify remembering the formulas, and demonstrates how to calculate voltage, current, and resistance in various scenarios. The video also includes practical examples and a challenge for viewers to test their understanding.

Takeaways

• 🔌 Ohm's Law is a fundamental principle in electrical engineering that describes the relationship between voltage, current, and resistance.
• 👨‍🔬 Ohm's Law was formulated by Georg Ohm, who conducted experiments to understand the effects of electrical current on the human body.
• 📚 There are three formulas associated with Ohm's Law: V=IR, I=V/R, and R=V/I, which can be remembered using Ohm's Triangle (V-I-R).
• 📈 Ohm's Triangle is a mnemonic device that helps to easily recall the correct formula by covering the variable you need to find.
• 📘 A free PDF guide with examples is available for those who need a reference and can be accessed on theengineeringmindset.com.
• 🔋 Voltage is akin to pressure in a circuit, pushing electrons through the wires and components.
• 💡 The intensity of current is directly proportional to voltage, meaning if the voltage doubles, the current also doubles.
• 🛠️ Resistance is the opposition to the flow of electrons and is used in circuits to control current and protect components.
• 🔍 The unit of current is the Ampere (or Amp), named after French physicist André-Marie Ampère, who conducted extensive experiments on electricity.
• 🔄 Current is inversely proportional to resistance, so doubling the resistance will halve the current.
• 🔧 A multimeter is an essential tool for electrical troubleshooting and understanding Ohm's Law in practice.

Q & A

What is Ohm's Law and what does it represent?

Ohm's Law is a fundamental principle in electrical engineering that describes the relationship between voltage, current, and resistance in a circuit. It states that the voltage across a conductor is directly proportional to the current flowing through it and the resistance of the conductor.

Who developed Ohm's Law and what was the basis of his experiments?

Ohm's Law was developed by German physicist Georg Ohm. He conducted numerous experiments, including measuring current by touching live electrical circuits, to observe the effects of varying levels of current on the sensation of pain.

What are the three formulas of Ohm's Law?

The three formulas of Ohm's Law are: 1) Voltage (V) equals current (I) multiplied by resistance (R), 2) Current (I) equals voltage (V) divided by resistance (R), and 3) Resistance (R) equals voltage (V) divided by current (I).

What is the Ohm's triangle and how is it used to remember Ohm's Law formulas?

The Ohm's triangle is a mnemonic device that helps to remember the relationships in Ohm's Law. It consists of the letters V, I, and R arranged in a triangle with V at the top. To use a formula, you write down the variable you need to find, cover it up in the triangle, and then use the remaining letters to construct the formula.

Why is current represented by the letter 'I' and not 'C' or 'A'?

Current is represented by the letter 'I' because it is derived from the French term 'intensite du courant', which means 'intensity of current'. The letter 'I' was taken from this term and has remained the standard notation for current.

What is the relationship between voltage and current as described in the script?

The script explains that current is directly proportional to voltage. This means that if the voltage is doubled, the current will also double, assuming resistance remains constant.

How does resistance affect the current in a circuit?

Resistance affects the current in a circuit in an inversely proportional manner. If the resistance is doubled, the current will be halved, and vice versa, assuming voltage remains constant.

What is the significance of using a multimeter in electrical circuits?

A multimeter is essential for troubleshooting and building electrical knowledge. It can measure voltage, current, and resistance, which are crucial for understanding and diagnosing issues in electrical circuits.

Why is resistance used in circuits and what is its purpose?

Resistance is used in circuits to reduce the current flow and protect components such as LEDs or lamps from excessive current that could damage them. By adding resistance, the current is controlled, ensuring the safe operation of the circuit.

What are the two problems presented at the end of the script for viewers to solve?

The two problems are: 1) If a lamp with a resistance of 240 Ohms is plugged into a 120-volt US outlet, what will the current be? 2) If the same 240 Ohm resistive lamp is plugged into a UK outlet and draws a current of 0.958 Amps, what is the voltage being applied?

Outlines

00:00

🔌 Introduction to Ohm's Law

In this introductory segment, Paul from theengineeringmindset.com explains the fundamental concept of Ohm's Law, which is a crucial principle relating voltage, current, and resistance in electrical circuits. He introduces the historical context by mentioning Georg Ohm, who developed the law through extensive experimentation. The segment introduces three formulas associated with Ohm's Law, which can be easily remembered using Ohm's triangle (V-I-R). Paul also provides a free PDF guide for further understanding and a calculator tool for solving Ohm's Law problems. The explanation includes a simple example of calculating voltage in a circuit with a known current and resistance.

05:01

🔋 Understanding Voltage and Current Relationships

This paragraph delves deeper into the relationship between voltage and current, illustrating how they are directly proportional. Paul uses the analogy of a water pump to explain this concept, where increasing the voltage results in an increased flow of electrons, similar to increasing water flow with a larger pump. The segment also covers how to calculate current using Ohm's Law, with an example involving a lamp and a power supply. The importance of a multimeter for electrical troubleshooting and knowledge is highlighted, along with the effects of resistance on current flow. The inverse relationship between current and resistance is demonstrated through examples of how doubling the resistance halves the current, and vice versa.

💡 The Role of Resistance in Circuits

Paul discusses the concept of resistance, its role in limiting the flow of electrons, and its importance in protecting circuit components such as LEDs. He explains how resistance can be calculated using Ohm's Law when voltage and current are known. The segment provides an example of calculating resistance for a lamp connected to a power supply and touches on the practical implications of resistance in circuit design, such as preventing component damage from excessive current. The video concludes with a challenge for viewers to apply their knowledge to solve two problems related to Ohm's Law, with solutions provided in the video description. Paul also encourages viewers to follow the channel on various social media platforms for more educational content.

Keywords

💡Ohm's Law

Ohm's Law is a fundamental principle in electrical engineering that describes the relationship between voltage, current, and resistance in a circuit. It is central to the video's theme as it provides the basis for understanding electrical circuits. In the script, Ohm's Law is introduced as a relationship developed by Georg Ohm, and its application is demonstrated through various examples and formulas.

💡Voltage

Voltage, often measured in volts, is the electric potential difference between two points. It is likened to pressure in the script, pushing electrons through a circuit. Voltage is a key component in Ohm's Law, as it directly affects the current flow. For instance, when the voltage is doubled in the example with the battery and resistor, the current also doubles.

💡Current

Current, measured in amperes or amps, is the flow of electric charge in a circuit. It is directly proportional to voltage, as shown when the script describes how doubling the voltage results in doubling the current. Current is also related to the intensity of the light in a lamp, with higher currents leading to brighter lights.

💡Resistance

Resistance is a property of materials that opposes the flow of electric current, measured in ohms. It is inversely proportional to current, as demonstrated in the script when increasing resistance results in a decrease in current. Resistance is crucial for protecting components in a circuit from excessive current.

💡Georg Ohm

Georg Ohm was a German physicist who formulated Ohm's Law. His experiments and findings are foundational to the understanding of electrical circuits and are the historical context for the video's subject matter. The script mentions Ohm's experiments, including his self-subjected tests to measure current.

💡Ohm's Triangle

Ohm's Triangle is a mnemonic tool used to remember the relationships in Ohm's Law. It consists of the letters V (voltage), I (current), and R (resistance) arranged in a triangle. The script explains how to use the triangle to easily derive the formulas for Ohm's Law without memorization.

💡Ampere

The ampere, or amp, is the unit of electric current. It is named after the French physicist Andre-Marie Ampere, who contributed significantly to the understanding of electromagnetism. The script uses the term 'Ampere' to explain why current is represented by the letter 'I'.

💡Electromotive Force (EMF)

Electromotive Force, abbreviated as EMF, is the electrical pressure that pushes electrons through a circuit. The script mentions that 'E' can be used instead of 'V' in Ohm's Law formulas, but encourages sticking to 'V' for simplicity.

💡Circuit

A circuit is a closed loop through which electric current flows. The script discusses various examples of circuits, including those with batteries and resistors, to illustrate the application of Ohm's Law.

💡Multi-meter

A multi-meter is a versatile measuring instrument used to troubleshoot and measure electrical properties such as voltage, current, and resistance. The script recommends getting a multi-meter for building electrical knowledge and provides links for purchasing one.

💡Direct Proportionality

Direct proportionality is a relationship where an increase in one quantity results in a proportional increase in another. The script explains that current is directly proportional to voltage, as shown when the voltage in a circuit is doubled, the current also doubles.

💡Inverse Proportionality

Inverse proportionality is a relationship where an increase in one quantity results in a proportional decrease in another. The script illustrates this concept by showing that when resistance in a circuit is doubled, the current is halved.

Highlights

Ohm's Law is a fundamental relationship between voltage, current, and resistance.

Georg Ohm, a German physicist, developed Ohm's Law through extensive experiments.

Three formulas for Ohm's Law are: V=IR, I=V/R, and R=V/I.

Ohm's triangle (V-I-R) is a simple mnemonic to remember the formulas.

A free PDF guide with examples is available for easy reference.

Current is represented by 'I', named after Andre Ampere's term 'intensite du courant'.

EMF (Electromotive Force) can be represented by 'E', but 'V' is commonly used in Ohm's Law.

Voltage is like pressure in a circuit, pushing electrons around the wires.

Doubling the voltage doubles the current, demonstrating a direct proportionality.

Resistance is the opposition to the flow of electrons.

Doubling the resistance halves the current, showing an inverse proportionality.

A free calculator is available on the website for checking Ohm's Law calculations.

A multimeter is essential for troubleshooting and building electrical knowledge.

The flow of electrons (current) is necessary for devices like lamps to function.

Resistance is used in circuits to reduce current and protect components like LEDs.

Problem-solving examples are provided to test understanding of Ohm's Law.

The relationship between voltage, current, and resistance can be tested with practical problems.

Engagement with social media platforms and theengineeringmindset.com is encouraged for further learning.

Transcripts

- Hey there guys, Paul here from theengineeringmindset.com

In this video we're going to be looking at Ohm's Law

to understand how it works as well as how to use it.

There are also two problems at the end of this video

for you to test your knowledge and see if you can solve.

So, what is Ohm's Law?

Ohm's Law is a relationship

between voltage, current, and resistance

and how they relate to each other.

Ohm's Law was developed by German physicist,

named Georg Ohm,

who undertook many experiments to develop his theory,

including measuring current

by touching the live electrical circuits

to see how much it hurt.

As you might imagine,

the higher the current, the more it hurt.

Now, there are three formulas we need to use for Ohm's Law,

but we don't actually need to remember these

and I'll show you a super easy tip in just a moment.

So, the three formulas we use for Ohm's Law are,

voltage equals current multiplied by resistance,

current equals voltage divided by resistance,

and resistance equals voltage divided by current.

If that seems like a lot to remember, then don't worry,

because we don't need to remember them.

All we need to remember is Ohm's triangle,

which looks like this.

So, you just need to remember these three letters in order.

V-I-R.

Then we just write those down in a triangle

with V at the top

and we draw a line to separate the letters.

In fact, you don't even need to remember those,

because I've made a free PDF guide for you

with some worked examples which you can keep on your PC

or your mobile and access wherever you need.

Links for that can be found

in the video description down below.

Now, all we do when we need to use a formula

is cover up the letter we need.

So, if we want to find the voltage,

then we write V =

and then we cover up the V in the triangle.

That leaves us with I and R,

so we write I multiplied by R,

which means voltage equals current multiplied by resistance.

You can write a little multiplication symbol in the triangle

between the two letters if it helps you.

Now, I know what you're thinking.

Why is current represented with a letter I

and not a C for current?

Or even a letter A for the unit of Ampere.

Well the unit of current is the Ampere or the Amp

and this is named after Andre Ampere, a French physicist.

A couple of hundred years ago,

he undertook lots of experiments,

many involved varying the amount of electrical current.

So, he called this intensite du courant

or the intensity of current.

So, when he published his work, they took the letter I

and it became standard until this day.

Now, you might also come across formulas where the letter E

is used instead of V.

The letter E stands for EMF, or Electromotive Force,

but don't worry about that,

just stick to using V and substitute V for E

if you see it used in Ohm's Law's questions.

Anyway, so by covering V,

we get voltage equals current multiplied by resistance.

If we want to find current

then we write down I =

and then we cover up the letter I in the triangle.

That gives us V and R,

so as V is above the R like a fraction

we can write V divided by R.

Therefore, current is equal to voltage

divided by resistance.

If we want to find resistance,

then we write down R =

and then we cover up R in the triangle.

That leaves us with V and I.

So, we write V divided by I,

which gives us resistance equals the voltage

divided by current.

Let's look at some examples for how to use these formulas.

First, let's see how we find voltage

and how it relates to the other parts.

Let's say we have a simple electrical circuit

with a battery and a resistor.

We don't know what the voltage of the battery is though.

The resistor is 3 Ohms

and when we connect a multi meter into the circuit,

we see that we get a reading of two Amps of current.

We want to find the voltage.

So, using Ohm's triangle, we can cover up the V

and that gives us V equals I multiplied by R.

We know the current is two Amps so we can write that in

and we know the resistance is three Ohms,

so we can write that in also.

Therefore, two Amps multiplied by three Ohms,

gives us six volts.

The battery is therefore six volts.

Now, if you want to check your answers for Ohm's questions,

then I've built a free calculator on the website.

You can just drop your numbers in

and it will do the calculation for you.

Links for that again, in the video description down below.

Coming back to the circuit, if we now double the voltage

by connecting two six volt batteries in a series,

we get 12 volts.

If we now connect this to the same circuit,

the current also doubles from two Amps to four Amps.

If we double the voltage again to 24 volts,

the current will also double to eight Amps.

So, what's the relationship here?

We can see that current is therefore

directly proportional to voltage.

If we double the voltage, we double the current.

Remember, voltage is like pressure,

it's the pushing force in the circuit.

It pushes the electrons around the wires

and we place things like lamps in the way of these electrons

so that they have to flow through these

and that causes the lamp to light up.

By doubling the voltage

we see that the current also doubles,

meaning that more electrons are flowing

and this occurs as we apply more pressure or more voltage.

This is just like if we were to use a bigger water pump

then more water will flow.

Okay, so what about finding current?

Let's say we now have a three Amp lamp

connected to a six volt power supply.

To find the current, we write down I =

and then we cover up I in the triangle.

That gives us V divided by R,

so current equals voltage divided by resistance.

We know the voltage is six volts

and the resistance is at three Ohms,

so the current is therefore two Amps

and that's what we see on the multi-meter.

By the way, if you don't have a multi-meter

then I highly recommend you get one.

It's essential for troubleshooting,

but also building your essential electrical knowledge.

I will leave some links down below

for which one to get and from where.

So, we saw what happens when we use a resistance

of three Ohms in the circuit,

but if we double the resistance to six Ohms

by placing another three Ohm lamp into the circuit,

the current halves are just one Amp.

If we double the resistance again to 12 Ohms,

the current will half again to .05 Amps.

We can visually see this because the lamps

will become less bright as the current reduces

from the increase in resistance.

So, what's the relationship here?

We can see that the current is inversely proportional

to the resistance.

When we double the resistance,

the current will decrease by half.

If we half the resistance the current will double.

Current is the flow of electrons

or the flow of free electrons.

For us to make this lamp shine,

we need to push electrons through it.

How do we do that?

We apply a voltage across the two ends.

The voltage will push the electrons.

The atoms inside the copper wire

have free electrons in their valance shell,

which means they can very easily move to other copper atoms.

They will naturally move to other atoms by themselves,

but this will be in random directions,

which is of no use to us.

For the lamp to turn on,

we need lots of electrons to flow in the same direction.

When we connect a voltage source,

we use the pressure of a battery to push the electrons

through the circuit all in the same direction.

For example, to power this 1.5 Ohm resistive lamp,

with a 1.5 volt battery,

requires one Amp of current.

This is equal to six quintillion,

two hundred and forty two quadrillion electrons

passing from the battery

and through the lamp every second.

And if you can achieve this,

then the lamp will stay at full brightness.

If the voltage or current reduces

or the resistance of the circuit increases,

then the lamp will become dimmer.

Okay, now let's look at finding resistance.

Say we have a resistive lamp

connected to a 12 volt power supply.

We don't know how much resistance is adding to the circuit,

but we measure the current at 0.5 Amps.

To find the resistance, we write down R =

and then we cover up the R in the triangle.

We're left with V and I,

so resistance equals voltage divided by current.

We know the voltage is 12 volts

and the current is 0.5 Amps,

so 12 divided by 0.5 gives us 24 Ohms of resistance.

Resistance is the opposition to the flow of electrons.

It tries to prevent electrons from flowing.

That's why we use resistance in circuits

to reduce the current and protect components such as an LED.

If we tied to connect an LED

directly to a nine volt battery,

it would blow out

because the voltage and the current are too high.

But, when we add a resistor into the circuit,

then these are reduced,

so the LED is protected and will shine brightly.

So, given the circuit, we can increase the current

by increasing the voltage.

Or we can also increase the current

by reducing the resistance.

We can also reduce the current by increasing the resistance.

Okay, time for you to test your skills.

Can you solve these problems?

I will leave a link for the answer and the solution

in the video description down below.

Problem one:

Let's say we have this lamp

which has a resistance of 240 Ohms.

If we plug this into an outlet in the US,

which uses 120 volts,

what will the current be?

Problem two:

If I plug the same 240 Ohm resistive lamp

into an outlet in the UK,

we get a current of 0.958 Amps.

So, what is the voltage being applied here?

Okay guys, that's it for this video,

but to continue your learning

then check out one of the videos on the screen now

and I'll catch you there for the next lesson.

Don't forget to follow us

on Facebook, Twitter, Instagram, LinkedIn,

as well as theengineeringmindset.com