Table of contents |
|
What is a Magnetic Field? |
|
Visualizing the Magnetic Field Lines |
|
Key Characteristics of Magnetic Field Lines |
|
Different Magnetic Field Lines |
|
The magnetic field is the region around a magnet (or a magnetic material or a current-carrying conductor) where magnetic forces can be detected.
It is a vector quantity, symbolized by B.
Magnetic fields are detected using magnetic needles or iron filings.
Michael Faraday introduced the concept of magnetic field lines to represent magnetic fields graphically.
A magnetic field line is an imaginary line such that the tangent at any point gives the direction of the magnetic field at that point.
These lines help visualize the strength and direction of the magnetic field.
1. Direction of Lines:
Outside a magnet: North → South
Inside a magnet: South → North
Hence, magnetic field lines form closed loops.
2. Magnetic Flux:
Magnetic flux (Φ) represents the total number of field lines.
The number of lines per unit area perpendicular to the field represents the strength (B) of the field.
The net magnetic flux through any closed surface is zero.
This is due to the absence of magnetic monopoles.
3. No Intersection:
Magnetic field lines never intersect.
If they did, it would imply two directions of the magnetic field at the same point, which is not possible.
4. Elastic Nature:
Magnetic field lines behave like stretched elastic strings:
They tend to contract longitudinally (attracting opposite poles).
They repel laterally (repelling like poles).
5. Field Strength and Density:
Denser lines → stronger field
If field lines are parallel and equally spaced, the field is uniform.
If field lines are diverging or converging, the field is non-uniform.
6. Lines in Magnetic Materials:
Magnetic field lines can enter or leave a magnetic material at any angle.
Magnetic field lines also exist within all magnetised materials.
7. Neutral Point:
A point where the net magnetic field is zero due to the cancellation of two or more magnetic fields.
At a neutral point, no magnetic field lines exist.
8. Gauss’s Law for Magnetism:
States that the net magnetic flux through a closed surface is always zero.
Mathematically:
This confirms the non-existence of magnetic monopoles.
Right-hand thumb rule:
If the thumb points in the direction of current, the fingers curl in the direction of magnetic field lines.
Field lines: Concentric circles around the wire.
Field strength: where I = current, r = radial distance from the wire.
Magnetic field lines form concentric circles around the wire.
At the center, field lines are straight and perpendicular to the plane of the loop.
The field at the center:
where R is the radius of the loop and x is the distance from the center along the axis.
A solenoid is a coil of many circular loops of wire stacked together.
Magnetic field inside: Strong, uniform, and parallel lines
Magnetic field outside: Very weak
Resembles the field of a bar magnet.
Field inside a long solenoid:
B=μ0nIwhere n = number of turns per unit length, I = current
88 videos|420 docs|88 tests
|
1. What are magnetic lines? | ![]() |
2. What are the characteristics of magnetic lines? | ![]() |
3. How are magnetic lines formed? | ![]() |
4. What is the significance of magnetic lines? | ![]() |
5. Can magnetic lines be influenced by external factors? | ![]() |