Velocity of an electron and Conservation of energy

In summary, an electron is projected from plate A, directly toward plate B, with an initial velocity of 2.0 x 10^7 m/s. The velocity of the electron as it strikes plate B is closest to 1.3x10^7m/s.
  • #1
kevnm67
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Homework Statement


A pair of charged conducting plates produces a uniform field of 12,000 N/C directed to the right, between the plates. The separation of the plates is 40 mm. In the figure, an electron is projected from plate A, directly toward plate B, with an initial velocity of 2.0 x 10^7 m/s.
A) The velocity of the electron as it strikes plate B is closest to:

Homework Equations



Conservation of energy

The Attempt at a Solution


Equation: qV= 1/2mv2 My answer: 1.3x10^7m/s
I tried the equation above based on what I gathered from my book but I am suppose to get 1.5x107 How do I use the conservation of energy to get this answer? Thanks for your help
 
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  • #2
kevnm67 said:
How do I use the conservation of energy to get this answer?
If no external work were done, there would be no change in total energy. But work is being done, which increases the total energy. Set the work done equal to the change in total energy (which is the sum of PE and KE).
 
  • #3
kevnm67 said:
So Work=qED or (1.6x10-19)(12000)(.04)= 7.68x10-17?
Not relevant. (And I have no idea where you're getting the numbers from--they weren't in your problem statement.)
and W= KE+PE
This is the only one you need.
PE= kqq/r
Not relevant.

kevnm67 said:
I tried the equation above based on what I gathered from my book but I am suppose to get 1.5x107
FYI, this answer is not correct. Why do you think it is?
 
  • #4
kevnm67 said:
I got the first one saying W = qED and plugged it in being you mentioned work being done and I thought that's what you use. 12000 is the charged produced and 1.6x10^-19 is the charge of an electron.
Are you sure you haven't mixed up this problem with a different one? See your first post.

W = KE + PE
Again, for this problem (the one in your first post) this is all you need. You are given W and KE, just solve for PE. (That really should be W = ΔKE + ΔPE.)
 
  • #5
I copied the wrong problem..sorry. I am going to edit and delete my previous posts.
 

1. What is the velocity of an electron?

The velocity of an electron refers to its speed and direction of motion. It is typically measured in meters per second (m/s) and can vary depending on factors such as electric and magnetic fields.

2. How is the velocity of an electron related to its energy?

The velocity of an electron is directly related to its kinetic energy. As the velocity increases, so does the kinetic energy of the electron. This is due to the fact that kinetic energy is calculated as 1/2 mass x velocity^2.

3. What is conservation of energy?

Conservation of energy is a fundamental principle in physics which states that energy cannot be created or destroyed, only transferred or converted from one form to another. This means that the total energy of a closed system remains constant over time.

4. How does conservation of energy apply to the velocity of an electron?

Conservation of energy applies to the velocity of an electron in the sense that the total energy of the electron must remain constant as it moves through an electric or magnetic field. This means that any changes in kinetic energy must be balanced by changes in potential energy.

5. Can the velocity of an electron violate conservation of energy?

No, the velocity of an electron cannot violate conservation of energy. This is because energy is always conserved in any physical process, including the motion of an electron. Any changes in the velocity of an electron must be accompanied by changes in other forms of energy to maintain the total energy of the system.

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