The two 5.0-cm-long parallel electrodes in the figure ( Figure 37.31 ) are space
ID: 1273188 • Letter: T
Question
The two 5.0-cm-long parallel electrodes in the figure(Figure 37.31) are spaced 1.0 cm apart. A proton enters the plates from one end, an equal distance from both electrodes. A potential difference ?V=500V across the electrodes deflects the proton so that it strikes the outer end of the lower electrode.
http://session.masteringphysics.com/problemAsset/1385291/3/38.P32.jpg
What magnetic field strength will allow the proton to pass through undeflected while the 500 V potential difference is applied? Assume that both the electric and magnetic fields are confined to the space between the electrodes.
What magnetic field direction will allow the proton to pass through undeflected while the 500 V potential difference is applied?
Explanation / Answer
E = V/d = 500/(0.01) = 50000 V/m
F = q E = 1.6e-19 * 50000 = 8e-15 N
a = F/m = 8e-15/(1.67e-27) = 4.79042e12 m/s2
y = 0.5 a t^2
==> t = sqrt(2y/a) = sqrt(2*(0.01/2)/(4.79042e12)) = 4.569e-8 s
==> v = x/t = 0.05/4.569e-8 = 1.0943e6 m/s
magnetic field:
B = E/v = 50000/1.0943e6 = 0.0457 T
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According to the right hand rule, the magnetic field is into the page.
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