HW20_pdf - mcconnell(kam2342 – homework20 – Turner –(60230 This print-out should have 5 questions Multiple-choice questions may continue on the

mcconnell (kam2342) – homework20 – Turner – (60230) 1 This print-out should have 5 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A static uniform magnetic field is directed into the page. A charged particle moves in the plane of the page following a clockwise spiral of decreasing radius as shown. B B Neglect the effect due to gravity. What is a reasonable explanation? 1. The charge is positive and with a constant speed. 2. The charge is neutral and slowing down. 3. The charge is positive and slowing down. 4. The charge is negative and slowing down. correct 5. None of these 6. The charge is neutral and speeding up. 7. The charge is neutral and with a constant speed. 8. The charge is negative and speeding up. 9. The charge is negative and with a con- stant speed. 10. The charge is positive and speeding up. Explanation: We know that when a charged particle moves in a uniform magnetic field with a constant speed, it undergoes a circular mo- tion with the centripetal force provided by the magnetic force, namely m v 2 r = q v B , so we know that the radius is in fact propor- tional to the speed, r = m q B v .