TBR Physics section 8 (2 Questions)

[AMSOHN]

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Hello,

I have two questions with regards to the end of the chapter problems 11 and 32:

#11) If the voltage across the plates are reversed, why would the (negatively charged) oil drops accelerate downward? Since the electric field's direction was originally upward, changing the voltage across the plates would alter the electric field direction downward. However, since the oil drop is negatively charged (hence, opposes the direction of the electric field) and there is a gravitational force, wouldn't the oil drop remain suspended in air?

#32) I'm feeling a bit of a dialectic tension with the explanation to the answer for this problem. The explanation says the KE doesn't change b/c the frequency doesn't change. However, at the same time, the ion would be emitted with a greater KE. What am I missing here? If the ion picks up KE every time it crosses the gap in the middle, wouldn't the frequency increase?

Thanks in advance,
AMSOHN

 

[altogether]

If electrons are being suspended then the field must be downwards (current is in the direction opposite the movement of electrons). I think this answers your 1st question...

Hello,

I have two questions with regards to the end of the chapter problems 11 and 32:

#11) If the voltage across the plates are reversed, why would the (negatively charged) oil drops accelerate downward? Since the electric field's direction was originally upward, changing the voltage across the plates would alter the electric field direction downward. However, since the oil drop is negatively charged (hence, opposes the direction of the electric field) and there is a gravitational force, wouldn't the oil drop remain suspended in air?

#32) I'm feeling a bit of a dialectic tension with the explanation to the answer for this problem. The explanation says the KE doesn't change b/c the frequency doesn't change. However, at the same time, the ion would be emitted with a greater KE. What am I missing here? If the ion picks up KE every time it crosses the gap in the middle, wouldn't the frequency increase?

Thanks in advance,
AMSOHN

 

[Fort]

Hello,

#32) I'm feeling a bit of a dialectic tension with the explanation to the answer for this problem. The explanation says the KE doesn't change b/c the frequency doesn't change. However, at the same time, the ion would be emitted with a greater KE. What am I missing here? If the ion picks up KE every time it crosses the gap in the middle, wouldn't the frequency increase?

Thanks in advance,
AMSOHN

The distance the ion covers increases with each loop. From v=d/t, if both the kinetic energy and distance increase, then the time the particle takes to go around should remain relatively the same. Thus, the frequency remains unchanged!