Magnetic Effects of Electric Current - MAGNETIC FIELD AND FIELD LINES12.1 MAGNETIC FIELD AND FIELD LINES12.1 MAGNETIC FIELD AND FIELD LINES12.1 MAGNETIC FIELD AND FIELD LINES12.1 MAGNETIC FIELD AND FIELD LINES
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A magnetic field is a region around a magnetic material or a moving electric charge within which the force of magnetism acts. It is a vector quantity, meaning it has both magnitude and direction.
The direction of the magnetic field at any point is the direction in which the North pole of a compass needle points when placed at that point.
Magnetic field lines are imaginary curves used to represent a magnetic field. By convention, field lines emerge from the North pole () and merge at the South pole () outside the magnet.
Inside the magnet, the direction of field lines is from its South pole to its North pole, forming continuous closed loops.
The relative strength of the magnetic field is shown by the degree of closeness of the field lines. The field is stronger where the field lines are crowded (near the poles).
No two magnetic field lines are found to cross each other. If they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is physically impossible.
The SI unit of magnetic field strength is the Tesla, denoted by the symbol .
📐Formulae
💡Examples
Problem 1:
Why do magnetic field lines form closed loops unlike electric field lines (from isolated charges)?
Solution:
Magnetic field lines form closed loops because magnetic monopoles do not exist. Since every magnet has both a North () and a South () pole, the lines emerge from and enter externally, then travel from to internally.
Explanation:
In magnetism, the flux must be continuous. Outside the magnet, the direction is , and inside it is . This completes the loop.
Problem 2:
If two magnetic field lines were to intersect at a point , what would happen to a compass needle placed at that point?
Solution:
If the lines intersected, the compass needle would have to point in two different directions simultaneously to align with both field lines at point .
Explanation:
A compass needle only shows the resultant direction of the magnetic field at a specific point. Since it cannot point in two directions at once, intersection is impossible.
Problem 3:
Where is the magnetic field strongest in a bar magnet?
Solution:
The magnetic field is strongest at the poles (North and South).
Explanation:
In a diagram of magnetic field lines, the lines are most densely packed near the poles. High density of lines represents high magnetic field strength ().