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This physics 2 prelab is killing me

  1. Jan 24, 2006 #1
    ok, i've been working on this 6 question prelab for over an hour, with 3 of my friends, and the best score we can get (so far) is a 2/5... something just isn't right.... the problem is, the program the teacher uses doesn't tell you which problem you missed. we have no idea, so i will post the 6 problems, and say how we got the answer we got, then, if you can, help in any way possible! haha

    question 1, i think we got right....
    The figure below shows the electric field lines for two point charges separated by a small distance. Determine the ratio q1/q2.
    [​IMG]
    a. 1/2, b. -1/2, c. 2, d. -2, e. 1, f. -1
    i t hink the ratio is 16/-8, so it would be -2 (d)

    question 2 is
    The figure below shows a test charge q between the two positive charges. Find the force (in newtons) on the test charge for q=3 micro Coulombs . Give a positive answer if the force is to the right and a negative answer if the force is to the left.
    [​IMG]
    so i found the force for both sides of the introduced charge. i got 262 as my answer, when i added the two charges together. i think my error was i was supposed to subtract them

    question 3 is
    For the previous question, find the electric field (in newtons/coulomb) at the position of test charge. Again, supply a positive value if the electric field points to the right and a negative value if it points to the left. (1)

    divide question 2 by the introduced charge (3 microcoulombs) meaning i got it wrong cause i did the first one wrong... might be fixed by subtraction

    question 4 is
    How much work (in joules) is done in moving a charge of 2.5μC a distance of 39 cm along an equipotential at 12~V?
    this one i just flat out couldnt find a formula to get this....

    question 5 i think we got right, found off a website
    Which of the following are valid units for electric field strength?

    A. N/m B. N/C C. V/m D. V/C
    i said b and c

    and the last question....
    The field lines associated with a uniform electric field in a region of space are shown in the figure below. Imagine drawing two equipotentials in the plane of the figure, one passing through point A and and one passing through point B. If the electric field is 450 N/C, how much does the potential change in going from A to B? Provide your answer in volts and use a positive value if it increases and a negative value if it decreases.
    [​IMG]

    what i did, was find the distance between the 2 using path theorem. then, used the formula delta U=-qEcos(theta) delta s
    so i used that, with delta s being the hypotenous, the angle i found with trig (angle a), and plugging the rest in. this is the problem that has confused me the most, and needs the most explaining...

    sorry for so much, but this is just terrible, we feel pretty dumb all of us getting 2's on it, but maybe i can fix that. thanks in advance for any help offered
     
  2. jcsd
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