Electron released into electric field

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Homework Help Overview

The problem involves an electron released from rest in a uniform electric field, where it accelerates vertically upward. The discussion centers on determining the magnitude and direction of the electric field and whether the effect of gravity can be ignored, with a focus on quantitative justification.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore kinematic equations to find average speed, final speed, and acceleration. There are attempts to relate acceleration to force and the electric field using the equation a = -eE/m. Questions arise regarding the validity of assumptions and the correctness of the approach.

Discussion Status

Participants are actively engaging with the problem, sharing calculations and questioning their reasoning. Some have provided numerical values for average and final speeds, while others express uncertainty about their methods and calculations. There is no explicit consensus, but the discussion is moving towards clarifying the relationships between the variables involved.

Contextual Notes

There is a mention of saving certain concepts, such as kinetic energy, for future discussions, indicating a structured approach to the topic. Participants are also considering the implications of gravity in their calculations.

that1grrl
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An electron is released from rest in a uniform electric field. The electron accelerates vertically upward, traveling 4.50m in the first 3.00us after released. What are the mag and direction of electric field and are we justified in ignoring the effect of gravity (justify quantitatively).

Im not sure where to start. Do I look for finding acceleration to use a=-eE/m to get the E? I just need a start.
 
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Yes. From kinematics, what's its average speed? what's its final speed?
What's its acceleration? What Force must act to provide that acceleration?
 
Ok so I may be grasping at straws but would I do this:
(using constant-acceleration formula)

v=4.5m/3X10^-6
v= 1.33x10^6m/s= (2a(4.50m))^1/2
a=1.98x10^11m/s^2

a=F/m
1.98x10^11m/s= F/9.11x10^-31kg

etc? Even close. Eventually my units don't work out so I am thinking this isn't the right track.
 
save the Kinetic Energy trweatment for next chapter...

v_average = 1.5E6 m/s , so v_final = 3E6 m/s , right?

(v_final)^2 = 2 a x ...

but a = v_final / t !
 
Last edited:
I think I got it. THANKS!
 

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