What Causes an Electron to Change Direction in an Electric Field?

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Homework Help Overview

The discussion revolves around the behavior of an electron in an electric field, specifically within a cathode ray tube setup. The problem involves understanding how an electron's velocity changes when it enters a region with an electric field, focusing on the concepts of force and acceleration.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the idea that the electron's direction changes while questioning whether its speed remains constant. There are discussions about the forces acting on the electron and the nature of acceleration in the electric field.

Discussion Status

The discussion is ongoing, with participants sharing their thoughts on the principles involved. Some have provided insights into the forces at play and the resulting changes in velocity, while others express uncertainty about the concepts and seek clarification.

Contextual Notes

Participants mention the influence of gravitational forces and the need to consider both horizontal and vertical components of velocity. There is a recognition of the complexity of the situation, particularly regarding the nature of acceleration experienced by the electron.

Neesha
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Homework Statement


a cathode ray tube contains parallel plates that are 30mm long and have an electric field strenght between them of 2.5x10^4. an electron traveling at 2.9x10^7m/s enters the field at right angles. explain why the electron experiences a change in velocity.

Homework Equations


The Attempt at a Solution


im thinking that only the direction of the electron changes but the speed stays the same. so the velocity changes in terms of direction. is that right?
 
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Neesha said:

Homework Equations


Do you have any idea of what principles you might need to apply?

Neesha said:

The Attempt at a Solution


You need to show some attempt before anyone at PF can help you.
 
okay i did make an attempt but I am not really sure about the principles i need to apply. i think only the direction changes but not the speed. but I am not sure why or if its true.
 
Neesha said:
okay i did make an attempt but I am not really sure about the principles i need to apply. i think only the direction changes but not the speed. but I am not sure why or if its true.

Well firstly what will cause a change in velocity?
 
probably the +ve plate attracting the electron
 
Neesha said:
probably the +ve plate attracting the electron

Which causes what type of force to be exerted on the electric charge?
 
electric force.i think that's what its called?
 
Listen no doubt the direction of velocity changes, but the electron also gathers a certain velocity in the upward direction towards the positive plate.And this velocity increases because of the constant acceleration the electron experiences.So now the net velocity of the electron is the resultant of both the initial horizontal component as well as the perpendicular component both in magnitude and direction.Got it??
 
yeah i get your last sentence but i thought the acceleration increased and that it wasn't constant.
 
  • #10
Neesha said:
yeah i get your last sentence but i thought the acceleration increased and that it wasn't constant.

Before the electron enters the electric field, it is in a gravitational field. So the effects of gravity are quite small. But as it enters the electric field, it causes an acceleration which affects the vertical component of its velocity.

F=ma=EQ.

So its horizontal velocity will stay the same, but the vertical velocity changes with time.
 
  • #11
oh ok yh thanks :)
 

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