Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A magnetic field is the region surrounding a magnet where the force of the magnet can be detected. It is a vector quantity having both magnitude and direction.
Magnetic field lines are imaginary lines used to represent a magnetic field. By convention, the 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.
Magnetic field lines are closed curves. The relative strength of the magnetic field is shown by the degree of closeness of the field lines; the field is stronger where the lines are crowded.
No two 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 not possible.
The magnetic field produced by a given current in the conductor decreases as the distance () from it increases. Mathematically, .
Right-Hand Thumb Rule: If you hold a current-carrying straight conductor in your right hand such that the thumb points towards the direction of current (), then your fingers will wrap around the conductor in the direction of the field lines of the magnetic field ().
📐Formulae
💡Examples
Problem 1:
Why do magnetic field lines not intersect each other?
Solution:
If two magnetic field lines intersected, then at the point of intersection, there would be two different directions for the magnetic field. This would mean a compass needle placed at that point would point in two different directions simultaneously, which is physically impossible.
Explanation:
This concept highlights the uniqueness of the magnetic field vector at any given point in space.
Problem 2:
A current through a horizontal power line flows in East to West direction. What is the direction of magnetic field at a point directly below it?
Solution:
According to the Right-Hand Thumb Rule, if the thumb points towards the West (direction of current ), the fingers will wrap around the wire. At a point directly below the wire, the fingers will point towards the South.
Explanation:
Applying the Right-Hand Thumb Rule: Current is East West. Placing the right thumb pointing West, the curled fingers move from North to South at the position below the wire.