Chapter 13. Magnetic Effects of Electric Current
Magnetic field: The region surrounding a magnet, in which the force of the magnet can be detected, is called a magnetic field.
Magnetic field lines: There are many lines forms around a magnet, which are originated from north pole and it seems to end with south pole of magent such line are known as magnetic field lines.
Properties of magnetic field lines:
(i) The magentic field lines emerge from north pole and merge at the south pole.
(ii) Inside the magnet, the direction of field lines is from its south pole to its north pole.
(iii) The magnetic field lines are closed curves.
(iv) The magnetic field is stronger, where the field lines are crowded.
(v) Two field lines do not intersect/cross each other.
Magnetic field lines do not intersect each other:
This is so, magnetic field lines do not intersect 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.
Magnetic field around a current-carrying conductor:
- An electric current through a metallic conductor produces a magnetic field around it.
- When a current carrying conductor is kept over a compass and parallel to its needle, when the direction of flowing of electric current reversed the deviation of compass is in opposite direction.
- If the current is increased, the deflection also increases.
- The magnitude of the magnetic field produced at a given point increases as the current through the wire increases.
- When we place the compass at a farther point from the conducting
wire, the deflection in the needle decreases.
Right-Hand Thumb Rule:
Imagine that you are holding 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. This is known as the right-hand thumb rule. This rule is also known as Maxwell’s corkscrew rule.
Magnetic Field due to a Current through a Circular Loop:
The magnetic field produced by a current-carrying straight wire depends inversely on the distance from it. Similarly at every point of a current-carrying circular loop, the concentric circles representing the magnetic field around it would become larger and larger as we move away from the wire.
Properties of magnetic field line of a current through a circular loop:
(i) At the center of this loop the magnetic field lines are a straight line.
(ii) Every point on the wire carrying current would give rise to the magnetic field appearing as straight lines at the center of the loop.
(iii) Section of the wire contributes to the magnetic field lines in the same direction within the loop.
- The magnetic field produced by a current-carrying wire at a given point depends directly on the current passing through it.
- if there is a circular coil having n turns, the field produced is n times as large as that produced by a single turn. This is because the current in each circular turn has the same direction, and the field due to each turn then just adds up.