Irene asked in Science & MathematicsPhysics · 3 months ago

What’s the magnitude of the charge on the oil doplet?

May I know why’s the answer A instead or B or C?

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  • NCS
    Lv 7
    3 months ago
    Favorite Answer

    The field is constant between the plates:

    E = V/x

    When the field points down, Newton's Second gives us

    ma = mg - qE = mg - qV/x

    which rearranges to

    mg = ma + qV/x ← #1

    And when the field points up,

    m*3a = mg + qV/x

    which rearranges to

    mg = 3ma - qV/x ← #2

    Subtrace #1 from #2 to get

    0 = 2ma - 2qV/x

    and so

    q = max / V

    Hope this helps!

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