1. PHYS 241 Recitation Kevin Ralphs Week 8

2. Overview HW Questions Magnetostatics Biot-Savart Law Gauss’s Law for Magnetism Ampere’s Law

3. HW Questions Ask Away…

4. Magnetostatics Electrostatics vs Magnetostatics – When we were talking about electrical phenomenon earlier in the course, we assumed we were at an equilibrium so no charges were moving – For our study of magnetism we will assume that our current is steady (or at least not varying rapidly) and that we are not too far away from our magnetic field source – Note that the principle of superposition is valid in both of these approximations

5. Biot-Savart Law

7. When running a Biot-Savart Law integral, it often becomes crucial to draw a picture to make sure you get the cross product correct FYI: If the magnetostatic approximation fails you would have to use the equation below!

8. Gauss’s Law for Magnetism

9. Why should I care? – Gauss’s law gives you important information about the shape of magnetic field lines – Essentially, magnetic lines of flux are loops and they never converge or diverge on a point Note: when there are no currents flowing, we can use the concept of magnetic “charge” to solve problems, but this is a theoretical tool only

10. Ampere’s Law

11. Although this isn’t called Gauss’s law, this idea functions much like Gauss’s law for electric fields. This means that all the details about Gauss’s law apply here – You must use a closed loop – The current is that which is enclosed by the loop: this plays the analog as the source of a magnetic field – A line integral is a sum: Just because it evaluates to zero, does not mean that the magnetic field is zero – You must already know something about the magnetic field prior to applying Ampere’s Law