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Magnetic Field III

Magnetic Field III. We have learned…. Magnetic force Applications of magnetic field To measure e/m Cyclotron Mass spectrometer Measurement of Sign and density of charge carriers. Plan of the lecture. The Torque on a Current Loop. Hall effect a revision…. The Hall effect.

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Magnetic Field III

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  1. Magnetic Field III

  2. We have learned…. Magnetic force Applications of magnetic field To measure e/m Cyclotron Mass spectrometer Measurement of Sign and density of charge carriers

  3. Plan of the lecture. • The Torque on a Current Loop

  4. Hall effect a revision….

  5. The Hall effect • Provides a way to determine sign and density of charge carriers. w conductor

  6. + + + + + + + + + + + + - - - - - - - - - - - - - - - - If electrons are majority charge carriers E E conductor EH B

  7. + + + + + + + + + + + + - - - - - - - - - - - - - - - - If the electrons are majority charge carriers - conductor VH +

  8. Density of charge carriers

  9. Convention • If the voltage of the lower terminal is negative, electrons are the majority charge carriers. • If the voltage of the lower terminal is positive, holes are the majority charge carriers.

  10. z n h y e g x f Torque on a current loop a makes angle  with the field b

  11. z e  y  b f

  12. z h  y  b g

  13. z n h y g x f Forces on a current loop  e b a y

  14. Forces on a current loop Contribute to torque

  15. z e  Fhe  Ffg f  y 

  16. Torque on a current loop • If loop has N turns

  17. Radial magnetic field is always parallel to the plane. Maximum torque.

  18. A positron is projected in a uniform magnetic field B, with its velocity making an angle  with the magnetic field. Find the (a) period (b) pitch and (c) radius of the helical path. Helical motion

  19. Find the magnitude and direction of force Problem 18 page 748

  20. B dF   Ring as seen from side view Element is into the board

  21. E 36 page 745 N = 20 a = 5 cm, B = 0.5 T Ans: 5 x 10-3 N-m

  22. L = 12.7 cm N = 13 turns M = 262 g P 19 page 748 Find the least current in the loop to prevent from rolling down the plane.

  23. Torque due to gravity Ans: I = 1.63 A

  24. Problem 6 page 746

  25. Problem 4 page 746

  26. A particle is moving in a plane which is perpendicular to a constant uniform magnetic field. Calculate the cyclotron frequency from Lorentz force equation.

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