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What we learned from last class

What we learned from last class. Hall effect: Determines the sign and number of carriers. Measures B. Define magnetic dipole moment by. where n is normal to the loop with RHR along I. Van Allen belts. Moving point charge:. Bits of current:. I.

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What we learned from last class

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  1. What we learned from last class • Hall effect: • Determines the sign and number of carriers. • Measures B. • Define magnetic dipole moment by where n is normal to the loop with RHR along I.

  2. Van Allen belts

  3. Moving point charge: • Bits of current: I The magnetic field “circulates” around the wire. Sources of Magnetic Fields Permeability constant Biot-Savart Law

  4. Magnetic field due to a current loop Principle of superposition: At the center, On axis generally,

  5. Circular Loop Current as a Magnetic Dipole

  6. Magnetic Field of Circular Arc Current I runs clockwise in the closed loop wires below: What is B at center?

  7. PHYS241 – warm-up A circular current loop lies in the plane perpendicular to this sheet with its axis along the x-direction, and produces magnetic field B as shown. What is the direction of the current at the top end of this loop? a. Out of the sheet b. Into the sheet c. Along +x axis d. Along x axis e. Current is zero. x

  8. sources Gauss’s Law for Magnetism Gauss’s Law Gauss’s Law for Magnetism No sources

  9. A constant magnetic field could be produced by an infinite sheet of current. In practice, however, it is easier and more convenient to use a solenoid. Magnetic field of a solenoid L R • A solenoid is defined by a current I flowing through a wire that is wrapped n turns per unit length on a cylinder of radius R and length L.

  10. Magnetic field of a solenoid (continued) Contribution to B at origin from length dx # turns in length dx one turn (or for L>>R) (half at ends)

  11. Long solenoid (R<<L): • B inside solenoid • B outside solenoid // to axis nearly zero (not very close to the ends or wires) Solenoid’s B field synopsis

  12. STAR RHIC STAR Experiment

  13. Magnetic field of a Straight Current y I Infinite straight current http://falstad.com/vector3dm/

  14. FB 1,2 FB2,1 B B I1 I3 Two Perpendicular Currents I2 FB 1,3

  15. PHYS241 - Quiz A A circular current loop lies on the xy-plane as shown, where the current is clockwise as seen from the positive z-axis. What is the direction of the B field at point A? z a. Along +x axis b. Along +y axis c. Along +z axis d. Along z axis e. Along x axis y I x A

  16. PHYS241 - Quiz B A circular current loop lies on the xy-plane as shown, where the current is clockwise as seen from the positive z-axis. What is the direction of the B field at point A? z a. Along +x axis b. Along +y axis c. Along +z axis d. Along z axis e. Along x axis y I x A

  17. PHYS241 - Quiz C A circular current loop lies on the xy-plane as shown, where the current is clockwise as seen from the positive z-axis. What is the direction of the B field at point A? z a. Along +x axis b. Along +y axis c. Along +z axis d. Along z axis e. Along x axis y I A x

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