Magnetic Permeability

Summary

In this AP Physics essentials video, Mr. Andersen explains the concept of magnetic permeability, the ability of materials to create internal magnetic fields. He uses a bar magnet and a compass to demonstrate the invisible magnetic field's effect on magnets. Iron filings are introduced to visualize these fields. The video further explores how the presence of materials like iron with high magnetic permeability warps magnetic fields, contrasting with materials like wood or aluminum that have low permeability. The use of electromagnetism to measure magnetic permeability and the significance of relative magnetic permeability are also discussed, highlighting iron's high value due to its molecular structure that readily supports magnetic field formation.

Takeaways

• 🧲 Magnetic permeability is the measure of a material's ability to create internal magnetic fields in response to an applied magnetic field.
• 🗺️ A magnetic field is an invisible force field that influences the behavior of magnets, as demonstrated by the interaction between two bar magnets.
• 🧭 A compass is a small magnet that aligns itself with the magnetic field, showing the direction and strength of the field.
• 📏 Iron filings can be used to visualize magnetic fields, showing the lines of force that align with the field's direction.
• 🌌 Free space, or a vacuum, has a magnetic permeability that is constant and serves as a baseline for comparing the permeability of other materials.
• 📐 The ratio of a material's magnetic permeability to that of free space is known as relative magnetic permeability, which indicates how strongly the material can be magnetized.
• 🌟 Materials with high relative magnetic permeability, such as iron, cobalt, and nickel, are more likely to be magnetic and can induce strong internal magnetic fields.
• 🔌 Electromagnetism principles can be used to measure magnetic permeability, as demonstrated by using a toroid and a magnetic sensor to measure the field created by a current.
• 🔩 The mu (μ) symbol represents the magnetic permeability of a material, and mu-naught (μ₀) represents the permeability of free space.
• 🔢 Materials like wood and aluminum have a relative magnetic permeability close to 1, indicating they have a low ability to support magnetic fields.
• 🧬 The molecular structure of a material, such as iron, determines its ability to induce magnetic fields and its overall magnetic properties.

Q & A

What is a magnetic field?

A magnetic field is an invisible area around a magnet where magnetic forces can act on other magnetic materials. It is the region through which the force of magnetism acts, and it is visualized by the way a compass needle aligns or by the pattern made by iron filings.

What is the role of a compass in understanding magnetic fields?

A compass is a small magnet floating on a needle that aligns itself with the magnetic field, showing the direction of the magnetic force. It helps visualize the presence and direction of the magnetic field around a magnet.

How can iron filings be used to demonstrate the existence of a magnetic field?

Iron filings can be sprinkled on a piece of paper placed above a magnet. The filings align themselves along the invisible magnetic field lines, revealing the shape and direction of the field.

What is magnetic permeability?

Magnetic permeability is the measure of a material's ability to allow a magnetic field to pass through it. It indicates how easily a material can support and create internal magnetic fields.

How does the presence of a material in a magnetic field affect its permeability?

If a material has high magnetic permeability, it can significantly alter the magnetic field, creating internal magnetic fields. If the material has low permeability, it does not change the magnetic field much, indicating a weaker ability to support magnetic fields.

What is the term for magnetic permeability in a vacuum?

The magnetic permeability of a vacuum is denoted by the symbol 'mu-naught' (μ₀) and is a constant value that serves as a baseline for comparing the permeability of other materials.

How can the magnetic permeability of a material be measured?

Magnetic permeability can be measured using an electromagnetism setup, such as a toroid wrapped with wire. By passing a current through the wire and measuring the magnetic field with a sensor, one can determine the material's ability to support magnetic fields.

What is the significance of relative magnetic permeability?

Relative magnetic permeability is the ratio of a material's magnetic permeability to that of free space (μ₀). It provides a comparison that indicates how much more or less a material can support magnetic fields compared to a vacuum.

Why is iron considered a good magnet?

Iron is considered a good magnet because it has a high relative magnetic permeability, which means its molecular structure can easily induce and support strong internal magnetic fields.

How do non-magnetic materials like wood and aluminum compare in terms of magnetic permeability to free space?

Non-magnetic materials like wood and aluminum have a relative magnetic permeability very close to 1, indicating they have a very low ability to support internal magnetic fields, which is why magnets do not stick to them.

What is the relationship between a material's molecular structure and its magnetic permeability?

A material's molecular structure plays a crucial role in its magnetic permeability. Materials with structures that can easily align with and support magnetic fields, like iron, have higher permeability and are more magnetic.

Outlines

00:00

🧲 Magnetic Permeability and Fields

This paragraph introduces the concept of magnetic permeability, which is the capacity of a material to generate internal magnetic fields. Mr. Andersen begins by explaining what a magnetic field is, using a bar magnet and a compass to demonstrate the invisible force that attracts the north and south poles. He then uses iron filings to visualize the magnetic field lines around the magnet. The paragraph delves into the definition of magnetic permeability, how it can be measured, and its significance in determining a material's ability to be magnetized. The permeability of free space is established as a baseline for comparison, with materials such as iron showing a high permeability due to their ability to warp the magnetic fields, indicating strong internal magnetic field generation.

05:05

🔬 Measuring Magnetic Permeability

The second paragraph focuses on the measurement of magnetic permeability using electromagnetism principles. Mr. Andersen describes an experiment involving a toroid, a donut-shaped object wrapped with wire, to measure the magnetic field created by an electric current. The permeability of free space, denoted as mu-naught, is measured by having no material inside the toroid. To measure a material's permeability, the material is placed inside the toroid, and the resulting magnetic field is compared to that of free space. The paragraph also introduces the concept of relative magnetic permeability, which is the ratio of a material's permeability to that of free space. Examples of relative permeabilities for various materials, such as wood, aluminum, cobalt, nickel, and iron, are provided, highlighting iron's exceptional ability to induce magnetic fields due to its molecular structure.

Keywords

💡Magnetic Permeability

Magnetic permeability is a measure of how easily a material can support the formation of a magnetic field within itself. It is a fundamental concept in the video, as it explains the ability of matter to create internal magnetic fields. The script uses the term to describe how different materials can either warp or have no effect on a magnetic field, indicating their relative magnetic permeability.

💡Magnetic Field

A magnetic field is the area around a magnetic material where magnetic forces can be detected. In the script, the concept is introduced by describing the interaction between two bar magnets and is further explained using a compass, which aligns itself with the invisible magnetic field. The magnetic field is visualized using iron filings, demonstrating the field's lines of force.

💡Compass

A compass is a navigational instrument that shows direction relative to the Earth's magnetic poles. In the video script, a compass is used as a tool to demonstrate the presence and direction of a magnetic field. The compass needle aligns itself with the magnetic field lines, indicating the north and south poles of the nearby magnet.

💡Iron Filings

Iron filings are small pieces of iron that can be used to visualize magnetic fields. The script describes placing a sheet of paper with iron filings over a magnet, which then align in the shape of the magnetic field lines, providing a visual representation of the invisible force.

💡Free Space

Free space in the context of the video refers to a vacuum, which is devoid of matter. It is used as a baseline to measure the magnetic permeability of other materials. The script explains that the magnetic permeability of free space remains constant over time and serves as a reference point for comparing the magnetic properties of other materials.

💡Magnetic Sensor

A magnetic sensor is a device used to detect and measure magnetic fields. In the script, a magnetic sensor is mentioned as a tool to measure the magnetic field created by an electromagnet, such as a toroid, which helps in understanding the concept of magnetic permeability.

💡Toroid

A toroid is a type of electromagnet shaped like a doughnut, with wire wrapped around it to create a magnetic field when an electric current is applied. The script uses the toroid to demonstrate how to measure the magnetic permeability of different materials by placing them inside the toroid and observing the effect on the magnetic field.

💡Relative Magnetic Permeability

Relative magnetic permeability is the ratio of a material's magnetic permeability to that of free space. It is used to compare the magnetic properties of different materials on a relative scale. The script explains that materials with higher relative permeability, such as iron, are more likely to be magnetic.

💡Cobalt, Nickel, and Iron

Cobalt, nickel, and iron are elements known for their strong magnetic properties. The script mentions these elements to illustrate materials with high relative magnetic permeability. For example, iron has a relative permeability of 200,000, which is significantly higher than that of non-magnetic materials like wood or aluminum.

💡Molecular Structure

Molecular structure refers to the specific arrangement of atoms within a material. The script discusses how the molecular structure of iron allows it to easily induce magnetic fields, making it an effective material for creating magnets. This highlights the importance of a material's internal structure in determining its magnetic properties.

Highlights

Magnetic permeability is the ability of matter to create internal magnetic fields.

A magnetic field is demonstrated by the interaction between two bar magnets or a bar magnet and a compass.

A compass is a small magnet on a needle that aligns with the magnetic field of a bar magnet.

Iron filings are used to visualize magnetic fields, showing their lines of force.

Magnetic permeability is a material's ability to create internal fields within a magnetic field.

Free space, or a vacuum, has a measurable magnetic permeability that serves as a baseline for comparison.

Materials with low magnetic permeability, like free space, do not alter the magnetic field significantly.

High magnetic permeability materials, such as iron, can warp and create strong internal magnetic fields.

Magnetic permeability can be measured using electromagnetism principles with a toroid and wire.

The mu-naught (μ₀) represents the magnetic permeability of free space and is a constant value.

Relative magnetic permeability is the ratio of a material's permeability to that of free space.

Materials like wood and aluminum have a relative magnetic permeability close to 1, indicating low magnetization ability.

Magnetic elements on the periodic table, such as cobalt and nickel, have higher relative permeability values.

Iron has an exceptionally high relative permeability of 200,000, making it an excellent magnet material.

Iron's molecular structure allows it to easily induce internal magnetic fields, contributing to its magnetic properties.

Understanding magnetic permeability helps in identifying materials' ability to support magnetic field formation.

The video provides a practical demonstration and explanation of magnetic permeability and its significance in physics.

Transcripts

Hi. It's Mr. Andersen and this is AP Physics essentials video 20. It is on magnetic permeability

which is the ability of matter to create internal magnetic fields. And we will get to that in

a second. But first let's address what a magnetic field is. So imagine I take a bar magnet that

has a north and a south pole and I hold another one right next to it and let it go. You know

what is going to happen . The north will quickly be attracted to the south of the other pole.

And that is why magnet are held together. But why is that? They are not touching but

there is something between them that is affecting their behavior. And so to study that we will

use a compass. And so I have the same bar magnet again. But I have a compass right down

below it. What is a compass? It is essentially a small magnet that is floating on a needle.

And you can see, same thing, that the north side of this compass is attracted to the south

side of the bar magnet. Let's move the compass a little bit. It is still pointing at the

south. Now let's move it over here. It is parallel to the magnet. And then we can see

now as we go to the other side the south is now facing the north. And so there is something

out there that is invisible that is affecting the magnet inside the compass. And so to visualize

that, lots of times we will use iron filings So you put a little bit of paper on top of

the magnet. Put some iron filings on there and then those fields are going to show up.

And now the property of the compass starts to make sense. And so it is lining up along

this magnetic field. And so as we move the compass over here it is again parallel to

those fields. Same thing over here. And same thing over here. So there are these magnetic

fields that emanate out from this magnet. And so if we take a compass and put it inside

an magnetic field it is just going to line up parallel. And so what is magnetic permeability?

Well if we take material and put it in that magnetic field its ability to create internal

fields is its magnetic permeability. And so if we put free space there, what is free space?

It is simply a vacuum. We can measure its magnetic permeability. And that is going to

be its internal ability to form magnetic fields. And it is going to remain constant over time.

So we can compare other material to the free space magnetic permeability and it tells us

something about their ability to be magnetized. And so now let's put some material in this

magnetic field. You can see that it is not changing the magnetic field at all. And so

we would say this has low magnetic permeability. If we were to compare that to free space it

looks essentially the same. And so if we were to put a ratio between those two it would

be a ratio of 1. Now let's put some material in the middle, like iron, that has high magnetic

permeability. And watch what happens to the magnetic field. It is warping those magnetic

fields. And so it is really creating these internal magnetic fields. And so if you have

high magnetic permeability, you are more likely to be a magnetic kind of material. So how

could you even measure such a thing? Well luckily we have a electromagnetism. In other

words magnetism is like electricity and vice versa. And so you can use an object like this.

It is essentially a donut wrapped in a wire. We call it a toroid. And then we can start

to measure the magnetic fields. And so as we wrap that wire around the toroid we can

add a current to it. And then we can just hold the magnetic sensor a little bit back

and we can measure the magnetic field that is being created. And so if you wanted to

measure the magnetic permeability of free space, how would you do that? You simply would

not have any thing inside that donut. It would just be wire wrapped around free space. And

so we can measure its free space magnetic permeability. And that iss mu-naught. And

so that is going to be the ability of a vacuum to create these internal magnetic fields.

Now if I wanted to measure the magnetic permeability of a material I could just put something where

the donut is. And so let's make a donut out of iron for example or a donut out of aluminum

or wood or whatever we want to put in the middle. Now we could measure its mu, which

is the magnetic permeability of that object or of that material. And so it is really important

since free space magnetic permeability is a constant that we can compare it to that.

So lots of times what you will see is the relative magnetic permeability. And all that

is is simply a ratio between the material's magnetic permeability and that of free space.

That is how lots of times it will be listed. And so if we were to look at some relative

magnetic permeabilities, what we are looking at here is the ratio of mu to mu-naught. If

we look at wood its value is going to be 1. Well, not exactly 1, but pretty darn close

to 1. And so that means it has a really low ability to form these internal magnetic fields.

If we look at aluminum it is also 1. So what do you know about aluminum? A magnet is not

going to stick to aluminum and that is because it can not induce these magnetic fields. But

if we were to look at elements on the periodic table that are magnetic, they are going to

have a much greater value when we are looking at the relative permeability. And so 250 for

cobalt. 600 for nickel and 200,000 for iron. So why is iron such a good magnet? It is because

its structure, its molecular structure on the inside is easily able to induce these

magnetic fields. And so did you learn the magnetic permeability measures the ability

of material to support the formation of these internal magnetic fields? And it also shows

us how magnetic they are going to be? I hope so. And I hope that was helpful.