Why Does the Shuttle-Ball Experiment Graph Show Only Straight Lines?

[superconduct]

Homework Statement

Homework Equations

The Attempt at a Solution

By the inverse proportionality relation between electric potential energy and distance, why is the graph composed of straight lines only but not concave upwards slopes? My sketch and the solution are attached below.

 

[TSny]

By the inverse proportionality relation between electric potential energy and distance, why is the graph composed of straight lines only but not concave upwards slopes?

When you say "inverse proportionality" between U and distance, are you thinking of U = kq₁q₂/r? That formula is for the potential energy of two point charges. But the problem deals with a point charge between parallel plates.

 

[superconduct]

yeah I was thinking of that.
So the relation when in parallel plates is linear? Why??

 

[TSny]

Can you describe the properties of the electric field between the plates?

 

[superconduct]

the electric field is nearly uniform and varies linearly across the plates?

 

[TSny]

the electric field is nearly uniform and varies linearly across the plates?

E is (nearly) uniform, which means that it essentially doesn't vary at all as you move from one plate to the other. So, what can you conclude about the force acting on the ball as it moves between the plates?

 

[superconduct]

The force is constant and work done varies linearly with distance?

 

[TSny]

The force is constant and work done varies linearly with distance?

Yes, that's right.

 

[superconduct]

thanks a lot for clearing my concepts :)