Calculating Time for Electron to Slow Down in Electric Field

  • Thread starter Thread starter Colts
  • Start date Start date
  • Tags Tags
    Electron Velocity
Click For Summary

Homework Help Overview

The problem involves calculating the time it takes for an electron to slow down in a uniform electric field. The electron has an initial velocity and is subjected to an electric field, with the goal of determining the time required for its speed to reduce to one fourth of its original value.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the relationship between electric fields and forces on charged particles, questioning how to apply Newton's second law to find acceleration. There is also exploration of the electron's charge and its implications for motion in the electric field.

Discussion Status

Some participants have offered guidance on using the force experienced by the electron to find acceleration and suggested using differential equations to relate acceleration to velocity over time. There are multiple interpretations of the calculations, and participants are exploring different methods to arrive at the time required for the electron to slow down.

Contextual Notes

Participants are working under the constraints of a homework assignment, which may limit the information they can use or the methods they can apply. There is also some uncertainty regarding the integration constants in their calculations.

Colts
Messages
76
Reaction score
0

Homework Statement



An electron with velocity v = 2.4 × 10^6 m/s i encounters an electric field E = 1250 N/C i. How long will it take for the speed to be one fourth its original value?

Homework Equations



Not sure

Maybe E = kQ/r^2

The Attempt at a Solution



I don't know where to begin. Looking at it makes me think it won't slow down because both are pointing in the positive i direction. Also, does an electron have a charge of -1.602 X 10 ^-19 C?
 
Physics news on Phys.org
The electron will slow down. Given some electric field and a charge, what is the force that will be experienced by the electron? Knowing this, how can you calculate the acceleration using Newton's 2nd Law? This should give you a good start. Your equation for an electric field is not needed since you are told what the (constant) electric field is for this problem.
 
Also, does an electron have a charge of -1.602 X 10 ^-19 C?
Right. And as it has a negative charge, it will slow down when it moves in the direction of the field lines.
Can you relate the electric field to a force on the electron?

Maybe E = kQ/r^2
This does not help.
 
So what I did was multiply E and the charge of an electron to find the force between them.
F= -2.0025 X 10^-16 N
Then using F=ma
when m = 9.109 X 10^-31 kg
I got a = -2.2 X 10^14 m/s^2

First, is this the direction I need to be going in or am I doing it wrong?
Second, if this is right, how can I use the a to find the velocity and time it takes?

Can I do the differential equation
dv/dt=a?
 
Last edited:
That is a good approach.
Can I do the differential equation
dv/dt=a?
You can use this to find the velocity as function of time, right. As the acceleration is constant, this is easy to solve.
 
I got the time for it to get to a fourth of the velocity to be 3 X 10^-9 s

That sound right? Is there a constant from the integration or will it be zero?

I also think it might be 8 X 10^-9 s by doing
v(0)=a(0)+c
v(0)= initial velocity
So c= the initial velocity.
 

Similar threads

Replies
1
Views
3K
Replies
12
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
Replies
5
Views
4K
  • · Replies 6 ·
Replies
6
Views
2K
Replies
4
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K