Magnetic Field and Magnetic Force/ Quantum Theory

Magnetic field produced by Electric Current

When there is a current flow through the conductor a magnetic field is produced in the region around the conductor. This effect is called the magnetic effect of electric current and was first demonstrated by Prof H.C.Oersted. He found that a magnetic needle placed near a current-carrying conductor gets deflected. Ampere’s swimming rule gives the direction of deflection of the needle. 

According to Ampere’s swimming rule, if a swimmer is swimming along the direction of the current in the conductor, facing the needle, then the north pole of the magnetic needle will deflect to his left. The nature of the magnetic field around the conductor depends on the geometry of the conductor. Let us learn more on the topic of magnetic field and magnetic force. 

Biot- Savart’s (Laplace’s) law

The magnetic field near a current-carrying conductor is given by Laplace’s law. According to this law, the magnetic field at a point is

1) Strength of the current through the conductor

2) Length of the current element

3) Sine of the angle between the current element and the line joining the point to the element

4) Square of the distance between the element and the point

Magnetic Force

If a current-carrying conductor is placed in a magnetic field, the moving charges in the conductor will experience a force due to the magnetic field. This can be called the mechanical effect of the electric field. The magnetic force on the moving charges is given by the expression

F = kBqVsinθ

F = force experienced by the moving charge

q = magnitude of the charge

Vsinθ = velocity in the direction perpendicular to the field

k = proportionality constant

Magnetic Flux

Magnetic flux through the surface is the number of magnetic lines of force passing through the surface in the normal direction. The magnetic field can be measured in terms of magnetic flux. Magnetic field or magnetic flux density is the number of magnetic lines of force passing through a unit area around the point in the normal direction. 

Properties of Magnetic Lines of Force

• Magnetic lines of force form closed loops
• Lines of force will never intersect
• Lines of force are close to each other in the region of the stronger field and spread out in the region of the weaker magnetic field
• They are equally spaced and parallel to each other in a uniform magnetic field

Fleming’s left-hand rule

The direction of the force on a current-carrying conductor placed in a magnetic field is given by Fleming’s left-hand rule. The law states that if the first three fingers of the left hand, the thumb, forefinger and the middle finger are stretched such that they are mutually perpendicular to each other with the forefinger in the direction magnetic field, the middle finger in the direction of the current then the direction of force is given by the thumb.

Do check BYJU’S page for more physics topics like Quantum theory. The quantum theory explains the phenomenon that occurs at the subatomic level. According to quantum theory, the energy of light is quantised.