1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Need help!

  1. Dec 13, 2005 #1


    User Avatar

    I need help on a few questions.

    1.An alpha particle has a positive charge of 2e and a mass of 6.6 x 10^-27 kg. With what velocity would the particle reach the negative plate of a parallel plate apparatus with a potential difference of 2.0 x 10^3 V.
    a)if it started from rest at the positive plate.
    b)if it started from rest at a point halfway between the plates.

    I got the answer for a, it 4.4 x 10^5 m/s. But i dont know how to do b.

    2. An electron is accelerated through a uniform electric field of magnitude 2.5 x 10^2 N/C with an initial speed of 1.2 x 10^6 m/s parallel to the electric field.
    a)Calculate the speed of the electron after it has travelled 2.5 cm in the field.

    I dont know how to do this one at all.

    3. Two electrons are fired at 3.5 x 10^6 m/s directly at each other.
    a)Calculate the smallest possible between the two electrons.

    I tried do Ee=Ek but that didnt work i kept getting the wrong answer. So can anyone please help me.
  2. jcsd
  3. Dec 13, 2005 #2


    User Avatar

    Staff: Mentor

    Well how did you do part 'a' of question 1? In part b, the acceleration takes place over half the distance. Hint: The electric field is contant between paralle plates.

    2. What is the force on a charge in an electrical field? Get F, and then solve for a. Then what is the equation for final velocity, initial velocity, acceleration and distance.


    3. Each electron has a kinetic energy and approach each other until they stop at some distance, at which point the energy is all electrical potential energy.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Need help!
  1. Need HELP! (Replies: 8)

  2. Need Help! (Replies: 1)