Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
History of electromagnetic theory wikipedia , lookup
Condensed matter physics wikipedia , lookup
Electric charge wikipedia , lookup
Field (physics) wikipedia , lookup
Maxwell's equations wikipedia , lookup
Neutron magnetic moment wikipedia , lookup
Magnetic field wikipedia , lookup
Electrostatics wikipedia , lookup
Electromagnetism wikipedia , lookup
Superconductivity wikipedia , lookup
Aharonov–Bohm effect wikipedia , lookup
Magnetic monopole wikipedia , lookup
Chapter 29 Magnetic Fields Physics 2212 Differences Between Electric Fields and Magnetic Fields 1) What creates the field a) Electric - charge created just by sitting b) Magnetic – current ultimately charged at source, but charge must be moving right hand current 2) Field Lines a) Electric – lines start and end b) Magnetic – circular loop lines Magnetic Versus Electric Field Lines Magnetic Field Lines • • • • Implies no magnetic charge (no North) No magnetic charges Always closed loop surrounding charge But still makes dipole with same shape Charges • Both electric and magnetic dipoles: opposites attract • North side of compass orients itself to face South, so that the dipole is opposite • Everywhere on Earth, there is a magnetic field – It produces a force A Magnet’s Effect • Charges move, producing the magnet’s effects • A force acts on the charges FB = q v × B q – charge v – velocity VECTOR B – magnetic field • This is a CROSS PRODUCT • Tricky – 3 mutually perpendicular vectors • Magnetic fields on Earth point North towards the magnetic South pole – Going into page X – Coming out of the page Example X X F X B P X v X FB = q v × B FB = IqI IvI IBI sinθ 0 when parallel Must move perpendicular X Right Hand Rule • V – Thumb • B – Finger • F – Palm • For point charge or current Current I = dq/dt l I = (dq/dt)l l (dq) = q (dl) l I = q (dl/dt) = qv FB = IqI IvI IBI sinθ F=IlXB Il **Must be a vector to get force!! Units • Units of B: Tesla (T) • T = Ns/Cm • A 1T magnet is BIG! A 19T magnet • Magnetic field with current pointed at it: bends path into circle or spiral • Old TV works like this: Cathode Ray – Resistor inside capacitor is heated, free electrons go into the positive end and shoot out hole, causing a beam – Current goes opposite of electrons – Must deflect the beam to other parts of screen magnetic field – Produce 2D field • 2 sets of charged coils – Side to side produces up and down – Up and down produces side to side Centripetal Force =qvB mv = qB r For a particle travelling in uniform magnetic field If you know “r”, the particles being bent measure ration, measure mass m = Br q v curving at different speeds Speed, strength, measure curvature • Mass spectrophotometer – separates ions of different mass • Consistent velocity – add electric field • Take beam, pass into magnetic field that pulls beam up, a capacitor that causes electric field to go straight through Fup = qvB Fdown = qE qvB = qE v=E B Curve up too fast, curve down too slowly, straight = right speed Charge is quantized (have same q) Loop of Current • No force on top and bottom • Causes torque – 1 parallel, 1 perpendicular – Makes spin FXF