PES 1120: Homework assignment 1 [24 points] Part 1: fully graded questions [18 points]

Transcription

1 PES 1120: Homework assignment 1 [24 points] Handed out: Friday January 31 Due in: Friday February 7, at the start of class Show all working and reasoning to receive full points. Part 1: fully graded questions [18 points] Question 1 [12 points] Three point charges, q 1, q 2, and q 3 are placed along a straight, vertical line as shown. At the point P, which is directly to the right of q 1, the net electric field created by three charges is zero. a)[2 points] If q 1 and q 3 are both positive charges, is q 2 positive or negative? For full points your explanation must include a diagram showing the three individual electric fields. b)[2 points] Assuming q 2 is negative, draw in a new diagram a sketch of the electric field lines that are present around the three point charges. c)[8 points] Assuming q 2 is negative and q 1 = 10 µc and the distance between the charges are as given in the diagram, find the values of q 2 and q 3. Question 2 [6 points] In an inkjet printer, letters are built up by squirting drops of ink at the paper from a rapidly moving nozzle. The ink drops, which have a mass of g each, leave the nozzle and travel toward the paper at 20 m/s, passing through a charging unit that gives each drop a positive charge q by removing some electrons from it. The drops then pass between parallel deflecting plates 2.5 cm long where there is a uniform vertical electric field with magnitude N/C. a)[4.5 points] If a drop is to be deflected 0.50 mm by the time it reaches the end of the deflection plates, what magnitude of charge must be given to the drop? Assume gravity is negligible. b)[1.5 points] Proof that it was OK in part a) to ignore gravity. Your reasoning must be supported by calculations. [Note : Similar to book problem on page 593 (9th edition) or page 637 (10th edition).]

2 Part 2: completion grade only [6 points] In this section you must fully complete 3 problems from the textbook to score 6 points in total. If you do everything correct in a problem, you will get 2 points for it. If you get something wrong but make a reasonable attempt, you will get 1 point for a problem. No attempt or an unconvincing attempt will score zero. To get the full 2 points you must: Write down all known and unknown variables clearly Draw a diagram Include all mathematical and logical steps, including assumptions Get the correct answer with the correct units and significant figures Please grade this section yourself using the answers at the back of the book. The grader will check that you have not cheated by awarding yourself too many points. This week s questions are: Chapter 21, Problem 51 [2 points] Chapter 22, Problem 19 [2 points] Chapter 22, Problem 49 [2 points]

3 PES 1120: Homework assignment 1 [24 points] Handed out: Friday January 31 Due in: Friday February 7, at the start of class Show all working and reasoning to receive full points. Part 1: fully graded questions [18 points] Question 1 [12 points] Three point charges, q 1, q 2, and q 3 are placed along a straight, vertical line as shown. At the point P, which is directly to the right of q 1, the net electric field created by three charges is zero. a)[2 points] If q 1 and q 3 are both positive charges, is q 2 positive or negative? For full points your explanation must include a diagram showing the three individual electric fields. b)[2 points] Assuming q 2 is negative, draw in a new diagram a sketch of the electric field lines that are present around the three point charges. c)[8 points] Assuming q 2 is negative and q 1 = 10 µc and the distance between the charges are as given in the diagram, find the values of q 2 and q 3. Question 2 [6 points] In an inkjet printer, letters are built up by squirting drops of ink at the paper from a rapidly moving nozzle. The ink drops, which have a mass of g each, leave the nozzle and travel toward the paper at 20 m/s, passing through a charging unit that gives each drop a positive charge q by removing some electrons from it. The drops then pass between parallel deflecting plates 2.5 cm long where there is a uniform vertical electric field with magnitude N/C. a)[4.5 points] If a drop is to be deflected 0.50 mm by the time it reaches the end of the deflection plates, what magnitude of charge must be given to the drop? Assume gravity is negligible. b)[1.5 points] Proof that it was OK in part a) to ignore gravity. Your reasoning must be supported by calculations. [Note : Similar to book problem on page 593 (9th edition) or page 637 (10th edition).]

4 Part 2: completion grade only [6 points] In this section you must fully complete 3 problems from the textbook to score 6 points in total. If you do everything correct in a problem, you will get 2 points for it. If you get something wrong but make a reasonable attempt, you will get 1 point for a problem. No attempt or an unconvincing attempt will score zero. To get the full 2 points you must: Write down all known and unknown variables clearly Draw a diagram Include all mathematical and logical steps, including assumptions Get the correct answer with the correct units and significant figures Please grade this section yourself using the answers at the back of the book. The grader will check that you have not cheated by awarding yourself too many points. This week s questions are: Chapter 21, Problem 51 [2 points] Chapter 22, Problem 19 [2 points] Chapter 22, Problem 49 [2 points]

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13 Chapter 21, problem 51 Chapter 22, problem 19

14 Chapter 22, problem 49