A monovalent ion enters into a plane-parallel capacitor. The entrance angle, alfa=30 degrees,up against armatures.Find the kinetik energy of the ion.

The ion comes out by keeping the same entrance angle(the value is positive).

The length of capacitor is l=10cm and electric field intensity, E=40KV/m.

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The problem is analogue to oblique projection in gravitational field, the only difference being that instead of gravitational acceleration g, we'll have the acceleration a=e*E/m

Then, the length of capacitor represents "tha range"

l=(v0^2/a)*sin 2 alfa=[m*v0^2/(e*E)]*sin 2 alfa

The kinetic energy is the semiproduct between the weight of the particle and it's square speed:

Ek=m*v0^2/2=e*E*l/(2 sin 2 alfa=0.37fJ=2.3KeV

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