IGCSE Physics 0625 – Simple Phenomena of Magnetism
4.1 Simple Phenomena of Magnetism
Objective
Describe the pattern and direction of magnetic field lines around a bar magnet.
What are magnetic field lines?
Magnetic field lines are a visual tool used to represent the direction and relative strength of a magnetic field. The key ideas are:
Lines emerge from the north pole (N) and enter the south pole (S) of a magnet.
The density of lines indicates the strength of the field – closer lines mean a stronger field.
Lines never cross each other.
Outside a magnet the field is continuous; inside the magnet the lines run from S back to N.
Pattern of field lines around a bar magnet
The pattern can be summarised as follows:
Lines leave the north pole, spread out in space, and curve around to re‑enter the south pole.
Inside the magnet the lines continue from the south pole back to the north pole, completing closed loops.
Near the poles the lines are dense (strong field); in the middle region they are more spread out (weaker field).
Direction of the field lines
To determine the direction at any point, use the “arrow” convention on the lines:
Arrows point away from the north pole.
Arrows point toward the south pole.
Inside the magnet the arrows point from S to N, completing the loop.
Thus, the magnetic field direction at a point in space is given by the tangent to the field line at that point, following the arrow.
Right‑hand rule for a bar magnet
If you grip the magnet with your right hand so that the thumb points toward the north pole, the curled fingers show the direction of the magnetic field lines around the magnet.
Summary Table
Feature
Outside the Magnet
Inside the Magnet
Origin of lines
North pole (N)
South pole (S)
Termination of lines
South pole (S)
North pole (N)
Direction of arrows
From N → S
From S → N
Line density (field strength)
Highest near poles, lower at centre
Uniform (conceptual)
Suggested diagram: Field lines emerging from the north pole of a bar magnet, curving around, and entering the south pole; arrows indicate direction; include interior lines from S back to N.
Key Points to Remember
Magnetic field lines form closed loops.
They start at the north pole and end at the south pole outside the magnet.
The direction of the field at any point is given by the tangent to the line, following the arrow.
Higher line density = stronger magnetic field.
Typical Examination Question
“A bar magnet is placed on a sheet of paper. Sketch the magnetic field lines around the magnet and label the direction of the field at points A (near the north pole) and B (mid‑way between the poles).”
Answer: Draw lines emerging from N, curving to S, with arrows pointing away from N and toward S. At point A the arrows point outward from the pole; at point B the arrows are roughly parallel to the magnet’s length, pointing from N toward S.