3. Magnetic Flux and Faraday’s Law

About this Lecture

Lecture

In this mini-lecture, we introduce magnetic flux and Faraday’s law. In particular, we: (i) define the magnetic flux as the number of field lines that penetrate a surface, and give the corresponding mathematical expression; (ii) consider how to alter our equation for magnetic flux of a coil with N turns; (iii) consider that when the magnetic field through a closed loop changes with time, this causes the magnetic flux to change with time, which induces a voltage called the electromotive force (EMF) that causes a current to flow in the circuit (a phenomenon known as Faraday’s Law); (iv) write down the equation relating EMF and magnetic flux, as well as the equation relating EMF, current, and resistance; and (v) list three ways to get a time varying flux.

Course

In this course, Professor Mohamed Anber (Durham University) explores magnetism. In the first mini-lecture, we discuss the magnetic fields of natural magnets and infinite wires carrying current. In the second mini-lecture we define the magnetic force and explore examples involving the magnetic force of one infinite wire on another. The third mini-lecture introduces magnetic flux in order to understand Faraday’s Law. In the fourth mini-lecture we turn towards an application of magnetism, the electric generator, and work through a calculation that gives us the electromotive force (EMF) of the electric generator. The fifth mini-lecture introduces a useful tool called the right hand rule that allows us to determine the direction of a magnetic field due to a wire carrying current, before introducing the principle of superposition and using these two new concepts in a variety of examples involving two infinite wires carrying current. The sixth and final mini-lecture goes over two demonstrations, the first involving natural magnets, and the second displaying Faraday’s Law.

Lecturer

Mohamed Anber is a Professor of Mathematical and Theoretical Particle Physics at Durham University. At the time of filming his course on magnetism, he was a Professor of Physics at Lewis & Clark College in Portland, Oregon in the United States. His research interests involve a broad range of theoretical physics topics, including those in quantum field theory and theoretical cosmology.