5) A circular coil of wire with 2,400 turns each of radius 18 cm carries a current of4.2 Amps directed CW (clockwise) as viewed from above. a) What is the magnetic field at the center of the loop? Magnitude: direction: [5] 3.51 x10'2 T , [5] down . b) If the same current is maintained, but the radius of the circular loop is made larger with the number of turns decreased (so the amount of wire remains the same), will the field at the center of the coil be [bigger, remain the same, or be smaller]? [2] smaller . 6) A solenoid has a length of 36 cm, a radius of 4cm, and 2,400 windings wound around it. A current of 4.2 amps flows through the solenoid. a) What is the magnitude of the magnetic field at the center of the solenoid? :2 .0352 [4] = .0343 T . b) Is this an "exac " or "approximate" calculation? [2] . C) Is the "approximate" value higher, the same, or lower than the "exact" value? [2] higher . d) In this case, by what percent does the "approximate" value differ from the "exact" value? [2] 2.4% . 7) A moving electron at a certain instant is located 7 mm West of a long straight wire that carries a current of 4.2 amps due North. a) If the electron is moving East (towards the wire) with a speed of4x105 mls, what is the magnetic force on the electron at this instant? Magnitude: direction: [4] 7.68 x 10'13 Mt , [4] North b) What is the acceleration that the electron will undergo at this instant if this is the only force on the electron? Magnitude: direction: [2] 8.44 x 1012 mils2 , [2] North . c) Will this acceleration speed up the electron, slow it down, turn it, or not affect the it's motion since the acceleration is zero? [2] turn it . d) lfthe electron were moving South (anti-parallel to the current) instead of East, would the magnitude of the magnetic force on the electron be greater, be the same, or be less? [2] same . e) lfthe electron were moving North (parallel to the current) instead, what would the direction of the magnetic force on the electron now be (if zero force, answer NIA). [2] West . 8) Consider the two currents in the figure below. a) Is the net magnetic force between the currents attractive, zero, or repulsive? [2] repulsive . b) What is the magnitude of the net magnetic force on the rectangular current? [6] 8.4 x 10'5 Mt . C) Is the magnitude of the net magnetic force on the straight current bigger, the same, or smaller than the magnitude of the net magnetic force on the rectangular current? [2] same . Iwire =4.2Amps; Irectangular = 3Amps, w = 20 cm; near distance to straight wire = 4 cm; distance from far side to straight wire = 12 cm . 20 cm ) lrectangular > 5 \"iii 12cm