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

[Neesha]

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?

 

[rock.freak667]

Homework Equations

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

The Attempt at a Solution

You need to show some attempt before anyone at PF can help you.

 

[Neesha]

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.

 

[rock.freak667]

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?

 

[Neesha]

probably the +ve plate attracting the electron

 

[rock.freak667]

probably the +ve plate attracting the electron

Which causes what type of force to be exerted on the electric charge?

 

[Neesha]

electric force.i think that's what its called?

 

[sagardip]

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??

 

[Neesha]

yeah i get your last sentence but i thought the acceleration increased and that it wasn't constant.

 

[rock.freak667]

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.

 

[Neesha]

oh ok yh thanks :)