Phy2005 Applied Physics II Spring 2017 Announcements:

Last Time DC motor: current loop in fixed magnetic field Switched I-direction here! “brushes”: electrical contact with moving commutator “commutator ring”

B = monI (const.!) For infinitely long solenoid Last time cont’d Solenoid: how to make a nearly constant magnetic field For infinitely long solenoid with tight coils, inside B = monI (const.!) n: number of turns/m Note: for such a solenoid B=0 outside B I B B = moI/(2pr) mo = 4 p x 10-7 Tm/A: permeability of vacuum

F F I - F = Q v B force on a moving charge Lorentz force F = I L B┴ dF = I (dL) B = (dQ/dt) dL B = dQ (dL/dt) B = dQ v B F dF dL F = Q v B force on a moving charge Lorentz force

Force by a magnetic field on a moving charge is always q v F q v F X x x x x q v F F v q v F q F = q v B┴ Force by a magnetic field on a moving charge is always Perpendicular to the direction of motion. NO WORK DONE BY THE FIELD!!!

My Old TV

This force causes a circular motion. Centrepetal force = FB X x x x x B r v FB = q v B Force by B-field q m This force causes a circular motion. Centrepetal force = FB Fc = mv2/r = q v B = FB r = mv/qB Since there is no work done by the field, in vacuum, The charge will make a circular motion forever!!!

Mass m? B = 0.36 T Mass spectrometer . . . . . r = 0.4 m . . . . . r = 0.4 m An object with +e charge And mass m kg A univalent ion with mass m Came into the field region with Speed v = 6 x 105 m/s. Mass m? Mass spectrometer

22-14 Each of the electrons in the beam of a TV tube has a momentum of 6.7 x 10-23 kg m/s. If the beam is traveling perpendicular to Earth’s magnetic field (0.71 G), how large is the radius of curvature of its path?

Clicker Quiz Time Log in your remote! ACADEMIC HONESTY Each student is expected to hold himself/herself to a high standard of academic honesty. Under the UF academic honesty policy. Violations of this policy will be dealt with severely. There will be no warnings or exceptions. Log in your remote!

q B 8.3 x 10-16 N into screen 1.6 x 10-2 N out of screen Q1. ( 22.9) A proton is moving in the direction shown with a speed of 5.0 x 106 m/s. The field has a magnitude of 0.135T. Find the magnitude and direction of the force on the proton if the angle is 50o. v q + B 8.3 x 10-16 N into screen 1.6 x 10-2 N out of screen 1.6 x 10-4 N along v 8.3 x 10-14 N into screen

Torque on a current loop DC motor: current loop in fixed magnetic field X X X X Switched I-direction here! Torque on a current loop q X B axis Depends only on magnetic moment of loop M=IA t = M B sin q q is angle between field and the axis of the loop!

22-26 A flat circular coil of 80 loops has a radius of 4cm. It is in a magnetic field of 600 G. How large is the torque on the coil when the axis of the coil makes an angle q with the field lines of a) 0 degrees? b) 30 degrees?