high importancemedium difficulty6 min

Field Lines

Field lines are imaginary lines used to show the shape, direction, and strength of a magnetic field.

In one line: Closer lines mean stronger field; crossing lines are never allowed.

Practice This Concept

Understand it

Field lines help us read a magnetic field visually.
They start from the north pole outside a magnet and enter the south pole.
Where the lines are closer, the magnetic field is stronger.
Where they are farther apart, the field is weaker.
In the lab and in diagrams, field lines help students understand how a compass would align in different positions.

Example

Around a bar magnet, the lines curve from the north pole to the south pole and do not intersect each other.

Formula and rule

Field lines outside a magnet go from north pole to south pole, and no two field lines intersect each other.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1If a compass is moved from the middle of a bar magnet to near its pole, the needle shows a larger deflection near the pole.
2This matches the diagram, because field lines are denser there.

Method you can reuse

1Identify the source magnet.
2Show lines leaving the north pole and entering the south pole.
3Make lines denser where the field is stronger.
4Never draw lines crossing.
5Add arrow direction if required.

Sketch it in your answer

Draw a bar magnet with several smooth curved lines from N to S. Show denser lines near the poles and wider spacing farther away.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

What does it mean when magnetic field lines are closer together near a pole?

Think first, then show answer

It means the magnetic field is stronger in that region. Closer field lines show greater magnetic intensity, so the pole region has a stronger effect on nearby magnetic objects.

Common wrong answer

A common wrong answer is to draw straight parallel lines around a bar magnet. That does not show the actual curved magnetic field pattern.

Don't mix this up

Students often think field lines are real wires or tracks. They are only a diagrammatic way to show field pattern.

Exam tip

If asked to draw field lines, keep the curves smooth, closed around the magnet, and never let two lines cross.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Draw magnetic field lines around a bar magnet, or state what field-line spacing tells us about strength.

1
Enough for 1 mark
Field lines are imaginary lines used to show the shape, direction, and strength of a magnetic field.
2
Add for 2 marks
Example: Around a bar magnet, the lines curve from the north pole to the south pole and do not intersect each other.
3
Add for 3 marks
Field lines help us read a magnetic field visually.

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