A magnet is an object that produces a magnetic field around itself.
During our childhood, we all have been marvelled by the properties of a bar magnet. It attracts tiny pieces of iron scraps and nails and repels another magnet when oriented in a particular manner. In this section, we will learn about the magnets, their properties and other related topics in further details.
Magnets are of two types:
- i) Natural magnets – Natural magnets occur in nature and have a weak magnetic field. Lodestones are a common example of natural magnets.
- ii) Artificial magnets – Artificial magnets can be produced by man-made means and have a stronger magnetic field. They can also be shaped as required. When an artificial magnet is shaped in the form of a bar, it is called a bar magnet.
A bar magnet is a rectangular piece of object, made up of iron, steel or any other ferromagnetic substance or ferromagnetic composite, that shows permanent magnetic properties. It has two poles, a north and a south pole such that when suspended freely, the magnet aligns itself so that the northern pole points towards the magnetic north pole of the earth.
Properties of Bar Magnet
A bar magnet has properties similar to any permanent magnet.
- It has a north pole and a south pole at two ends. Even if you break a bar magnet from the middle, both the pieces will still have a north pole and a south pole, no matter how many pieces you break it in.
- The magnetic force of it is the strongest at the pole.
- If this magnet is suspended freely in the air with a thread, it will not come to rest until the poles are aligned in a north-south position. A Mariner’s Compass uses this property to determine direction.
- If two bar magnets are placed close to each other, their unlike poles will attract and like poles will repel each other.
- A bar magnet will attract all ferromagnetic materials such as iron, nickel and cobalt.
Magnetic field lines
Let us understand the concept of magnetic field lines using the following activity. Let us sprinkle iron filings on a sheet of paper and a bar magnet in between. When we tap the paper, we notice that the fillings get aligned in the manner shown in the figure below.
The magnetic field lines can be defined as imaginary lines that can be drawn along the magnetic field that is acting around any magnetic substance. The magnetic field lines possess certain properties,
- The magnetic field lines of a magnet form continuous closed loops.
- The tangent to the field line at any point represents the direction of the net magnetic field B at that point.
- The larger the number of field lines crossing per unit area, the stronger is the magnitude of the magnetic field B.
- The magnetic field lines do not intersect.
The Pole strength of a bar magnet can be measured by moving it along an ‘infinite’ wire and carefully measuring the amount of current that is created. The formula for calculating the pole strength is:
p = the Strength of the magnetic pole,
W = the work done while moving the magnet around the wire,
I = the electric current in the wire.
Alnico and Neodymium Bar Magnet
It will be incomplete to talk about bar magnets and not mention Alnico bar magnet and neodymium bar magnet. The primary components of Alnico magnets are aluminium, nickel, cobalt, and iron. These magnets produce a strong magnetic field and retain their magnetic property even under extreme heat. Neodymium bar magnets are made with a mixture of neodymium, boron, and iron. These are both extremely powerful magnets but very brittle.
To learn more about the bar magnet, its magnetic field lines and the magnet used as a solenoid and other related topics, download Byju’s The Learning App.