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Homework Help: Oh no, conceptual questions, I need help

  1. Apr 24, 2007 #1
    Hey all, I have some hard times with these critical thinking questions. Please help me out. Thanks.

    1. The magnitude of the electric field at a point in space does not depend upon...
    a. The distance from the charge causing the field.
    b. The sign of the chrge causing the field.
    c. The magnitude of the charge causing the field.
    d. The force that a unit positive charge will experience at that point.
    e. The force that a unit negative charge will experience at that point.

    I guess you use these equations:
    F = k_e \frac {Q_1 Q_2} {r^2}
    E = \frac {F}{q_0}

    2. The magnitude of the electric field at a distance of 10 meters from a negative point charge is E. What is the magnitude of the electric field at the same location if the magnitude of the charge is doubled?

    I'd say 2E since it is directly proportional?

    3. A charged particle is moving in a uniform, constant magnetic field. Which one of the following statements concerning the magnetic force exerted on the particle is false?
    a. It does no work on the particle.
    b. It increases the speed of the particle.
    c. It changes the velocity of the particle.
    d. It can act only on a particle in motion.
    e. It does not change the kinetic energy of the particle.

    Uhm... I chose e because it is in a constant magnetic field?

    4. A proton traveling due north enters a region that contains both a magnetic field and an electric field. The electric field lines point due west. It is observed that the proton continues to travel in a straight line due north. In which direction must the magnetic field lines point?
    a. Up
    b. Down
    c. East
    d. West
    e. South

    I'm bad in right hand rule, but wouldn't it be up?

    5. A proton is traveling south as it enters a region that contains a magnetic field. The proton is deflected downward toward the earth. What is the direction of the magnetic field?
    a. Downward, toward the earth
    b. West
    c. North
    d. East
    E. South

    Um... I use the right hand rule again right? :grumpy: Downward?
    Last edited: Apr 24, 2007
  2. jcsd
  3. Apr 25, 2007 #2
    2 is ok
    3 is wrong
  4. Apr 25, 2007 #3
    1:The sign has nothing to do with the magnitude value
    2:Youre right
    3:Magnetic field does not do any work on the particle. The speed remains constant even though the velocity varies. Hence kinetic energy is always the same.
    4:No, it would be downwards
    5:Draw it out. It helps. East.
  5. Apr 25, 2007 #4
    Did you use the 2nd right hand rule for the last question?
  6. Apr 26, 2007 #5


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    Gold Member

    What do you mean the "2nd right hand rule"? You just use the standard RHR - you know the direction of the force and the velocity, so point your thumb and palm in the right directions and see where your fingers are pointing.
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