A beam of protons is injected into the velocity selector at right. The magnetic

Question

A beam of protons is injected into the velocity selector at right. The magnetic field is 20 mT out of the page. If the protons are to have a speed of 0.6c (c = the speed of light), find the size and the direction of the magnetic force acting on the protons. What magnitude of the electric field is required to select protons at 0.6c? Is the top plate positively or negatively charged? Explain your reasoning! If the beam is replaced with a beam of electrons traveling at the same speed, do the electrons pass through velocity selector undeflected, strike the upper plate, or strike the lower plate? Explain your reasoning!

Explanation / Answer

A) F = q v x B =1.6*10^-19*0.6*3*10^8*0.020 = 5.76*10^-13 N in downward direction

B) E = F/q = 5.76*10^-13 / (1.6*10^-19) = 3600000 N/C

Top plate is negatively charged because to counter magnetic force electric field should be in upward direction

C) They will pass undeflected, because the magnetic force will acts upwards and electric force will act downward

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