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Unformatted text preview: gilvin (jg47854) – 3. Electric Field 1 – meyers – (21235) 1 This printout should have 26 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. This homework is due Tuesday, February 1, at midnight Tucson time. 001 10.0 points Two small spheres carry equal amounts of electric charge. There are equally spaced points ( a , b , and c ) which lie along the same line. a b c + − What is the direction of the net electric field at each point due to these charges? 1. a b c + − 2. a b c + − 3. a b c + − 4. a b c + − 5. a b c + − correct 6. a b c + − 7. a b c + − 8. a b c + − 9. a b c + − 10. a b c + − Explanation: Since the field originates from positive charges and terminates on the negative charges, a b c + − 002 10.0 points A droplet of ink in an industrial inkjet printer carries a charge of 2 × 10 − 10 C and is deflected onto paper by a force of 0 . 0003 N. Find the strength of the electric field to produce this force. Correct answer: 1 . 5 × 10 6 V / m. Explanation: Let : F e = 0 . 0003 N and q = 2 × 10 − 10 C . The electrical force is F e = E q E = F e q = . 0003 N 2 × 10 − 10 C = 1 . 5 × 10 6 V / m . 003 (part 1 of 2) 10.0 points In 1909 Robert Millikan was the first to find the charge of an electron in his nowfamous oil drop experiment. In the experiment tiny oil drops are sprayed into a uniform electric field between a horizontal pair of oppositely charged plates. The drops are observed with a magnifying eyepiece, and the electric field is adjusted so that the upward force q E on some negatively charged oil drops is just sufficient to balance the downward force m g of gravity. Millikan accurately measured the charges on many oil drops and found the values to be gilvin (jg47854) – 3. Electric Field 1 – meyers – (21235) 2 wholenumber multiples of 1 . 6 × 10 − 19 C — the charge of the electron. For this he won the Nobel Prize. If a drop of mass 4 . 99592 × 10 − 13 kg remains stationary in an electric field of 9 × 10 5 N / C, what is the charge on this drop? The acceler ation of gravity is 9 . 8 m / s 2 . Correct answer: 5 . 44 × 10 − 18 C. Explanation: Let : m = 4 . 99592 × 10 − 13 kg , E = 9 × 10 5 N / C , and g = 9 . 8 m / s 2 . When suspended, m g = E q q = m g E = (4 . 99592 × 10 − 13 kg) (9 . 8 m / s 2 ) 9 × 10 5 N / C = 5 . 44 × 10 − 18 C . 004 (part 2 of 2) 10.0 points How many extra electrons are on this particu lar oil drop (given the presently known charge of the electron)? Correct answer: 34. Explanation: Let : e = 1 . 6 × 10 − 19 C . The number of electrons can be calculated from the charges on the oil drop: N = q e = 5 . 44 × 10 − 18 C 1 . 6 × 10 − 19 C = 34 ....
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 Spring '11
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 Magnetism, Work, Electric charge, N/C, Enet

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