Magnetic Field and Field Lines

Every person has heard and has an idea of what a magnet is. Magnets are substances that have the properties of attracting certain metals such as nickel, iron, cobalt, and so on. On the other hand, the property of attraction is called magnetism, and magnetism is mediated by a magnetic field. These are simple rules which magnets follow and are a major part in the field of physics.

Students of Class 7 Maharashtra board are introduced to the concept of magnetic field and field lines which will help them understand the concepts and build the foundation for future Physics classes. This article has provided an in-depth explanation on magnetic field and field lines from which students can build a proper understanding of the concepts and be confident. Read on to know more about the topic.

What is a Magnetic Field?

Magnetic field can be defined as the region surrounding the magnet from which the force of the magnet can be detected. A magnetic field in a magnet is created by electric current and magnetic dipole which imparts magnetic forces on other particles such as iron that are inside the magnetic field. Moreover, it has a vector quantity that has both magnitude and direction. However, one thing which is important to note is that the magnetic field of two magnets repel each other. To have a better understanding of magnetic fields students can check the image below and the properties of magnetic fields given in this article.

Properties of Magnetic Field

There are certain properties that magnetic fields follow and it is important for Class 7 Maharashtra Board Physics students to have an idea of the concepts as it will help them master the concept. The properties of magnetic field are as follows:

• The magnetic field lines emerge out of the north pole of the magnet and enter through the south pole.
• Magnetic field force acts at a distance just like gravitational and electric forces and is similar to an electric field surrounding a charge.
• The force with which the magnetic poles attract or repel other magnetic poles of other magnets are called magnetic force.
• Magnetic field is denoted by the symbol B

What are Magnetic Field Lines?

Magnetic field lines are the imaginary lines that attract other magnetic poles towards the magnet. For example, if a magnet is placed on a table filled with iron filings, then the iron filings will uniformly align themselves in different lines. These curved lines are the magnetic fields. Magnetic field lines always begin from the north pole and end on the south pole of the magnet and the field lines are the path along which an isolated unit north pole would move along in the field.

Properties of Magnetic Field Lines

The properties which dictates magnetic field lines are as follows:

• Magnetic field lines are closed and continuous curve lines which start from the north pole and end at the south pole after which it again returns to the north pole through the interior of the magnet.
• Magnetic field lines come closer to one another near the poles of the magnet but are separated at other places of the magnet.
• The field lines are crowded and are strongest near the pole and the further from the pole is the weakest. However, parallel and equidistant magnetic field lines represent an uniform magnetic field just like the Earth’s magnetic field.
• Two magnetic field lines cannot intersect each other and if they do it would mean that there are two directions of magnetic field at that point which is not possible.

Magnetic Force

We know that a magnetic field is produced by a magnet or a charge in motion. The magnetic field can apply some force to magnetic materials. Interestingly, the magnetic field cannot apply a force on a stationary charge but can apply force on a moving charge.

The force on a charge in motion is given by the charge multiplied by the cross-product of the velocity and magnetic field. The image given below will give a proper idea to students how magnetic force acts.

How to Calculate Magnetic Field?

The magnetic field is a vector quantity, and the total magnetic field at a point is given by the vector sum of individual magnetic fields at that point.
Bnet→=B1→+B2→+B3→+……
For continuous bodies,
The net magnetic field is given by integrating the magnetic field due to the differential element of the continuous body.
Bnet→=∫dB→

Magnetic Force on a Current Element

Magnetic force on a current-carrying wire due to a magnetic field is given by,
F→=i(dl→×B→)
Fleming’s Left-hand rule
The direction of the force in the above equation is in the direction of the cross product, (dl→×B→). Fleming’s left-hand rule simplifies it. According to Fleming’s left-hand rule, if we align the index finger in the direction of the magnetic field and the middle finger in the direction of the current, then our thumb points towards the direction of the force on the current-carrying wire.

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