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

AI Thread Summary
An electron in a cathode ray tube experiences a change in velocity when it enters an electric field due to the force exerted by the field. While the electron's horizontal speed remains constant, its direction changes as it accelerates towards the positive plate, resulting in a vertical component of velocity. The acceleration is constant, leading to a resultant velocity that combines both horizontal and vertical components. The gravitational effects are negligible compared to the electric force acting on the electron. Thus, the electron's trajectory is altered primarily by the electric field's influence.
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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