TBR PASSAGE QUESTION PHYSICS

[pizza1994]

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It's the Electrostatics chapter, passage III, Q 11 (P 154).

On occasion, the electrons are made to pass through the plates undeflected. If the electrons enter the region between the plates with the same direction, but with excessive velocity:

A) they will be deflected upward
B) they will be deflected downward
C) they will remain undeflected
D) they will be turned back the way they came

I dont get why the answer is B)....does anyone who has the book help me out on this? thanks

 

[Sed8&Intub8]

The magnetic field goes from the positive plate to the negative plate pushing the electron downward.

 

[pizza1994]

The magnetic field goes from the positive plate to the negative plate pushing the electron downward.

but the particle accerlates in the direction of the magentic force and that force then wouldnt it be going out of page if the field points from positive to negative (bascally pointing up)?

 

[IslandStyle808]

but the particle accerlates in the direction of the magentic force and that force then wouldnt it be going out of page if the field points from positive to negative (bascally pointing up)?

No, the magnetic field is perpendicular to the electric field (magnetic field is going into the page and electric field going top to bottom, I will explain). The electric field is going from the top of the page to the bottom, and the electric force goes in the same direction as the field. This is due to the plates of the CRT.

The magnetic force needs to be set up in such a way that it counters the electric force. This is why the magnetic force goes from the bottom of the page to the top. In order for this to happen, the magnetic field has to be pointing into the page. This is generated by the coils around the plate.

The reason why the electron is being deflected downward is because of the increased effect of the magnetic force. Remember the equation F (magnetic) =qvB. As the velocity increases, this would increase the force, and this would lead and upward movement of a positively charged species. Notice I said positive species, since we are dealing with an electron we are dealing with a negative charge. Thus the opposite would happen, and the electron would be deflected downward.

Hope this help.