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PHYS 221 Recitation. Kevin Ralphs Week 5. Overview. HW Questions Right-Hand Rule Warning Magnetic Fields. HW Questions. Ask Away…. Right-Hand Rule and the Cross Product. Cross product is perpendicular to BOTH of the vectors in the product
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PHYS 221 Recitation Kevin Ralphs Week 5
Overview • HW Questions • Right-Hand Rule • Warning • Magnetic Fields
HW Questions Ask Away…
Right-Hand Rule and the Cross Product • Cross product is perpendicularto BOTH of the vectors in theproduct • You sweep your hand from thefirst vector to the second throughthe smallest angle between • Measures how perpendiculartwo vectors are
Right-Hand Rule and the Cross Product • It’s also possible to do these calculation algebraically, if you are given the vectors by knowing some basic properties of the cross-product (no right-hand rule needed!!!) • Anti-Commutative: • Bilinear: ) • Cyclical in our Cartesian basis vectors:
Warning • There are multiple equations in this chapter that have • It is CRUCIAL that you understand which situations each equation is for so you don’t misapply them
Magnetic Fields • Source • Moving Charges • This is true even for permanent magnets • Shape • Always form closed loops: this means there is no magnetic charge • Always curl around the direction charges are moving in a right-handed way for positive charges • Negative charges reverse the direction of the field
Magnetic Fields • Lorentz Force • What does it tell me? • The force a charged particle experiences in an electromagnetic field • For a wire this becomes
Magnetic Fields • The magnetic force is always perpendicular to the velocity of a charge • This gives some important results: • Magnetic fields do no work: magnetic forces do not change the speed of a particle, so the kinetic energy is constant ergo no work is done • Magnetic forces cause charges to move in loops or helices