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Friday, May 25, 2012


The Class of 2012 is now done, and my heartfelt congratulations to all of you! This is a tremendous group of young women and men who are set to take on the top colleges in the country, and make their mark on the world! I am truly proud to have worked with each and every one of these students.

Sunday, May 20, 2012

If you want a 3-D simulation that will allow you to view electric fields for a wide variety of charged systems, check out this Falstad simulation site. It is really a useful visual display!

Sunday, May 6, 2012

Charged Particles in B-fields

Here's a case of charged particle flying through magnetic fields, and what happens to those particles. We know that fundamentally magnetism is formed by moving charges. So the moving charged particle has its own magnetic field. This field interacts with any external magnetic field, thus creating a magnetic force. We know this goes as F = qv x B. It is a cross product. But this then means the force is perpendicular to the motion of the particle. The consequence of this condition is circular motion, or mv^2/R = qvB. This video will show ActivPhysics simulations to get a sense of the 3-D nature of this motion. If the particle comes in 90-degrees to the magnetic field, we get a circular orbit. If the particle comes in at any angle other than 90-degrees or 0-degrees (parallel) to the field, then there is a component of motion perpendicular to the field (circular motion), as well as a component parallel to the field, which means no force and it keeps moving in that direction. A spiral/helix/corkscrew results! I also show a simulation of a mass spectrometer, where we use the circular motion to measure the mass of particles or ions. Check it out.

Thursday, May 3, 2012

Check out Rotating Pulleys

Check out how to find the TWO tensions in the same rope for a real, spinning pulley problem. The video is here. Also, check out small oscillations (like a pendulum) here, or a more complicated one here.