Electricity & Magnetism 201

Let’s start by trying to understand what is magnetic dipole first before we go any further.

Magnetic dipole, generally a tiny magnet of microscopic to subatomic dimensions, equivalent to a flow of electric charge around a loop. Electrons circulating around atomic nuclei, electrons spinning on their axes, and rotating positively charged atomic nuclei all are magnetic dipoles. The sum of these effects may cancel so that a given type of atom may not be a magnetic dipole. If they do not fully cancel, the atom is a permanent magnetic dipole, as are iron atoms. Many millions of iron atoms spontaneously locked into the same alignment to form a ferromagnetic domain also constitute a magnetic dipole. Magnetic compass needles and bar magnets are examples of macroscopic magnetic dipoles.”

Excerpt from https://www.britannica.com/science/magnetic-dipole

Exam Tip

  • d.c motor requires electrical supply in order to create movement. Thus electrical energy is converted into kinetic energy. 


Heating effect of electric currents

  • Collisions of electrons with lattice atoms:
    • when there is current, there will be an electric field. The effect of the electric field within a metal conductor is to accelerate the free electrons.
    • Electrons gain KE as they move through metal conductor.
    • Electrons collide with metal atoms in inelastic collisions which result in them losing the energy to the metal atoms. The electric field will then accelerate the electrons until next collision then the process repeats.
    • Metal atoms vibrate about their equilibrium positions with increased KE, hence increase in temperature of the metal conductor.
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