Properties of Magnetic Field Lines Around a Bar Magnet

Viraj is a very curious child just like you and me.

For his birthday, Viraj was gifted a bar magnet by his uncle.

Since then, he was fascinated by magnets and constantly played with it.

He knew that magnets attract metal pieces (such as iron nails).

But a weird thing he noticed was, whenever he put that metal piece really far away, magnets had a hard time to pull it.

Now, his curiousness about magnets increased. And he wanted to know how magnets attracted metal pieces.

And especially, why a magnet can only attract the nails which are near to it but not the ones which are far away.

Let’s help Viraj clear his doubts by teaching him about Magnetic Field of Lines

The magnet Viraj has is a bar magnet. It is a permanent magnet.

This magnet has two poles.

Magnets have a field around them. And if we place an iron nail in that field, it will experience a force of attraction by the magnet.

Let’s see how the magnetic field looks around a Magnet

Let’s take a plastic sheet and place it over the bar magnet.

Now, we have to take some iron filings and just sprinkle them over the plastic sheet.

Because of the magnet’s attraction, the iron fillings arrange themselves on the plastic sheet around that magnet.

The pattern formed by iron fillings shows the magnetic field around the magnet.

Now, let’s draw lines with a pen over the pattern.

If we look at the lines, we can notice that these lines form a continuous closed loop.

These field lines originate from the North pole and travel outwards searching for a south pole.

At the south pole, they enter the magnet again

Inside the Magnet, field lines travel from the South Pole to the North Pole

Magnetic field lines don't intersect with any other line.

If we draw a tangent to the field lines at any point, it gives the direction of the magnetic field.

The tangent shows the direction of where the field line is heading towards.

Now if there are more lines, that says that magnet can attract objects that are far away easily.

So, if the iron nails are inside the field lines, then magnet can attract them easily. ⇒ The more the lines nearby ⇒ The more the attraction force.

When Viraj placed the iron nail really far away, the magnet’s field of lines is really weak at that point and it couldn’t pull the nail.

⇒ The less the magnetic field lines nearby ⇒ The less attraction force on the nail. That’s why magnets have a hard time pulling objects that are far away objects.

Revision

Magnetic Field is the area where an object can feel the attraction force of the magnet.

Magnetic Field lines are closed loops. They don’t intersect.

Outside magnet - They travel from north to south. Inside magnet - they travel from south to north.

The End