<p>Use the following values for mass and charge: an electron has mass me = 9.11&

Question

<p>Use the following values for mass and charge: an electron has mass me = 9.11&#215;10-31 kg and charge &#173;e, a proton has mass mp = 1.67&#215;10-27 kg and charge +e, an alpha particle has mass malpha = 6.65&#215;10-27 kg and charge +2e, where e = 1.60&#215;10-19 C. An electron is released from rest in a vacuum between two flat, parallel metal plates that are 13.0 cm apart and are maintained at a constant electric potential difference of 700 Volts. If the electron is released at the negative plate, what is its speed just before it strikes the positive plate? <br />I know the answer to the first part is 1.57x10^7 m/s</p>
<p>But what I need help with is this</p>
<p><a name="15">What is the kinetic energy of the electron in units of eV? </a></p>

Explanation / Answer

The potential of the electron at release = kinetic at the upper plate

so V*q = 1/2*m*v^2

so v = sqrt(2*V*q/m) = sqrt(2*700*1.60*10^-19/9.11*10^-31) = 1.56x10^7m/s


From the definition of an electron volt we E = 700eV

or you can convert from Joules to eV

K = 1/2*m*v^2 = 1/2*9.11x10^-31*(1.56x10^7)^2 = 1.108x10^-16J

so E = 1.108x10^-16/1.60x10^-19 = 700 eV

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