Use the following values for mass and charge: an electron has mass m e = 9.11×10

Question

Use the following values for mass and charge: an electron has mass me = 9.11×10-31 kg and charge -e, a proton has mass mp = 1.67×10-27 kg and charge +e, an alpha particle has mass malpha = 6.65×10-27 kg and charge +2e, where e = 1.60×10-19 C. An electron is released from rest in a vacuum between two flat, parallel metal plates that are 11.0 cm apart and are maintained at a constant electric potential difference of 790 Volts. If the electron is released at the negative plate, what is its speed just before it strikes the positive plate?

and What is the kinetic energy of the electron in units of eV?

Explanation / Answer

Force on electron = -e E

Since field is from positive plate to negative plate, Force is towards postive plate.

accleration = eE /m

So electron starts at rest

From equations of motion

v^2 = 2 *a *s

Kinetic energy = 0.5 m V^2 = m *a *s   = F *s   = e * E * (distance between plates) = e * (Voltage between plates)

So K.E = 1.6 *10^-19 * 790 V = 790 eV

v = sqrt (790 * 1.6 * 10^-19 / ( 0.5 * 9.1 * 10^-31))

= 1.66 * 10^7 m/s

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