AAMC Self Assessment Physics #64

[tripkramer]

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In order to accelerate the ions in the correct direction, the electric field in the region between the two plates of the device in Figure 1 should be directed toward:

(A) top
(B) bottom
(C) left
(D) right

A: D because positive ions are accelerated between the two plates and the electric field must be directed towards the same direction the ions are to be accelerated.

I understand this, but how is it known that ions accelerated between the two plates are positive?

Thanks.

 

[mokhoras]

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[PostItsGalore]

The passage mentioned in line 2 that the atoms are ionized by removing the electrons. These 'ionized' atoms are then injected into the area between the two accelerating plates. Since the electrons are removed, they are now positively charged atoms.