Properties of Magnetic field lines with diagram

Earlier we have discussed the Electric field and Electric field lines. Similar to the electric field lines, there exist magnetic field lines in a Magnetic field. In this article, we are going to discuss the definition and the properties of Magnetic field lines and the diagram of magnetic field lines for a bar magnet, solenoid, straight wire and circular wire.

Contents in this article:

  • What are the magnetic field lines?
  • What is the physical significance of magnetic field lines?
  • Direction of Magnetic field lines
  • Properties of magnetic field lines
  • Magnetic field lines around a bar magnet
  • Magnetic field lines of Solenoid
  • The Magnetic field lines due to a straight current carrying wire
  • Magnetic field lines due to a current carrying circular wire
  • Why the magnetic field lines are closed curves?
  • Why two magnetic field lines never intersect each other?

What is magnetic field line?

If we place a unit North pole of a needle or compass in an external magnetic field it will deflect or move continuously due to the magnetic force on it. Now if we draw a path or line by joining the positions of the North pole during its motion then the line will be called a magnetic field line. It has the other name as Magnetic lines of force. There will be an infinite number of magnetic field lines in the magnetic field region. All the field lines are imaginary lines.

Physical significance of magnetic field lines

The physical significance of the magnetic field lines is that the tangent at any point on the magnetic field line gives the direction of magnetic field at that point.

Direction of magnetic field lines

Magnetic field lines start from the north pole and end at the south pole outside the magnet. So the direction of magnetic field lines is from North pole to South pole.

Properties of magnetic field lines

All the properties of magnetic field lines are as below-

  1. Magnetic field lines are imaginary lines.
  2. Magnetic field lines start from the North pole of a magnet and end at the South pole.
  3. Unlike the electric field lines, magnetic field lines are closed lines. This is a major difference between electric field lines and magnetic field lines.
  4. The tangent at any point on the magnetic field line gives the direction of the magnetic field at that point.
  5. Two magnetic field lines never intersect each other.
  6. Magnetic field lines are straight lines in a uniform magnetic field i.e. when the magnetic field is constant in a region.

Field lines for various type of magnet

Here we are going to draw the magnetic field line for a Bar magnet, a Solenoid, a straight wire and a circular wire.

Properties of Magnetic field lines around a Bar Magnet

Magnetic field lines around a Bar Magnet
Magnetic field lines around a Bar Magnet
  1. Magnetic field lines start from the North pole and end at the South pole outside the magnet. But inside the bar magnet, the magnetic field lines start from South pole and end at North pole.
  2. The density of field lines is smaller at outside than that of at inside the bar magnet. So, the strength of the magnetic field is greater at the pole and inside the bar magnet.
  3. Magnetic field lines are curved lines at outside whereas the field lines are straight lines inside the bar magnet.

Properties of Magnetic Field lines of Solenoid

Magnetic field lines of a Solenoid
Magnetic field lines of a Solenoid

When a current passes through the solenoid a magnetic field arises inside it. That means Solenoid behaves like a magnet. So it will have North and South poles as shown in the diagram.

  1. There is a uniform magnetic field inside the Solenoid. So, Magnetic field lines are straight lines inside the solenoid.
  2. At outside the magnetic field is non-uniform and the field lines are curved lines.
  3. The density of field lines is greater at the poles than at any other point outside the solenoid. So, the strength of the magnetic field is greater at the pole and inside the solenoid.

Magnetic Field lines for a current carrying straight wire

Magnetic field lines for a current carrying straight wire
Magnetic field lines for a current carrying straight wire

The magnetic field lines around a straight current carrying wire are the closed circular lines. Strength of magnetic field is same at every point on a circular field line.

Magnetic Field lines for a Current carrying circular wire

Magnetic field lines due to a Current carrying circular wire
Magnetic field lines due to a Current carrying circular wire

The magnetic field lines for a current carrying circular wire is shown beside. Here we have taken a clockwise current through the circular wire.

Why the magnetic field lines are closed curves?

Magnetic monopole does not exist. A magnet always has a North pole and a South pole. Therefore, Magnetic field lines start from the North pole of the magnet and end at the South pole of the same magnet as both poles exist there. Thus the magnetic field lines are always closed curves.

Why two magnetic field lines never intersect each other?

We know that the tangent at any point on the magnetic field line gives the direction of the Magnetic field at that point. Now if two magnetic field lines intersect at any point then we will get two tangents at that point due to the two field lines. That means we can get two directions of the magnetic field at that point. But a single point cannot have two directions of the magnetic field. Therefore, two magnetic field lines never intersect each other.

This is all from this article. If you have any doubt on this topic you can ask me in the comment section.

Thank you!

Related posts:

  1. Magnetic field – origin, definition and units
  2. How to find the direction of Magnetic field?
  3. Properties of electric field lines.
  4. Definition, properties and examples of electromagnetic waves