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    "An electron enters the gap between two plates at right angles to the electric field in the middle of the plates. On entry, it is travelling at 0.5c.The potential difference between the horizontal 0.2m long plates is 20kV with the positive plate at the top, 0.05m above the negative plate. Answer the following 6 questions.

    1. Determine the force due to gravity.
    2. Determine the force due to the electric field
    3. Determine the acceleration (assuming a constant acceleration throughout)
    4. Determine if the electron hits the top plate, and if so, where. Assume a constant acceleration.
    5. Determine the electric potential at the centre of the gap between the plates (both vertically and horizontally).
    6. Calculate the electric field strength at the same point."

    I currently do not understand how to work out questions beyond and including number 4, help with understanding would be great!

    Edit: Currently second guessing my answers for the previous questions so help with all would be nice

    1, The force due to gravity on the electron is its weight. I'm sure that you can work that out.
    2. The force due to the electric field can be got by first working out the electric field strength (using the expression for electric field strength between parallel plates), and then using the definition of electric field strength in terms of force and charge.
    3. Combine the above results to find the resultant force on the electron (you should notice something here that makes this very easy, in terms of the numbers you actually want to use). You can not work out the acceleration of the electron using a very fundamental relationship.
    4. This is effectively a projectile motion problem.

    I need to brush up on electric potential myself before carrying on!

    For 4, calculate the net force on the electron.
    For 5, we know that the force is constant, so you can apply E = Fx.
    For 6, what do you know about the electric field between two plates?
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Updated: March 13, 2016


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