Thread: electron question that I don't understand how to respond to.

This two part question really throws me because I don't really understand what it means.

Part one:
At different times,a proton and electron are placed equidistant from a point charge. How do the magnitudes and directions of the forces acting on them compare? Why?

Part two:
How do the accelerations and directions of travel of the electron and proton compare? Why?


What in the heck is a point charge?
Thank you.

A point charge is just an electrical charge that can be viewed as concentrated at a mathematical point. In other words, you don't have to worry about the geometry of the object that is generating the charge, you just need to worry about the quantity of charge. Does that make sense?

Ok, that makes sense.
However, this brings up another question: what do they want out of my answer? The polarity of the charge is undefined, so am I supposed to answer for both positive and negative instances?
If so would this answer satisfy the first part of the question?

The magnitude and direction of would be the same in either instance since, the direction is dependant on the polarity of the charge. If the charge was positive the the field would point away from the charge, if it was negative then the field would point toward the charge. In either case the magnitude would be approximately the same.

If the electron and proton are placed equidistant from a point charge,
then they lie on the circumference of a circle with the point charge at the centre.
The forces will differ depending on the proximity of the electron and proton.
They could be at opposite ends of a diameter or quite close.

Yes, you will have to answer with the possibilities of a positive or negative point charge in mind. The forces on the objects depend on the signs of the charges involved, the magnitude of the charges involved, and the distances between the charges involved.

For the second part, since you're asked about accelerations, the radically different masses of the proton and electron will figure largely.

Originally Posted by Archie Meade

If the electron and proton are placed equidistant from a point charge,
then they lie on the circumference of a circle with the point charge at the centre.
The forces will differ depending on the proximity of the electron and proton.
They could be at opposite ends of a diameter or quite close.

True, but the question said that they were placed there at different times-- so I assume that to mean that they are not orbiting simultaneously. I had not considered that possibility, however, if that is the case, then how would I answer that? The question gives very little info for me to work with, so I'm feeling a ittle lost....

Originally Posted by Ackbeet

Yes, you will have to answer with the possibilities of a positive or negative point charge in mind. The forces on the objects depend on the signs of the charges involved, the magnitude of the charges involved, and the distances between the charges involved.

For the second part, since you're asked about accelerations, the radically different masses of the proton and electron will figure largely.

Ok then...
So would these answer be workable?

Part one:
If the point charge had a negative sign, then it would attract the proton and repel the electron.
If the point charge were positive, then it would attract the electron and repel the proton.
The magnitude would be dependant on the distance between the charge and the particle, the greater the distance between the two, the weaker the effect would be .

Part two:
The acceleration of the proton would be slower than that of of the electron due to its greater mass compared to the elecrton, regardless of direction. The direction of the protons acceleration would be dependant on the sign of the charge; if positive then It's acceleration would be away from the charge, if negative than the proton would accelerate toward the charge. Similarly(Conversely), the electron would have greater acceleration because of It's smaller mass relative to the proton, regardless of direction. If the charge were negative, the electron would accelerate away from the charge. If the charge had a positive sign, then it would attract the electron.

Am I close?

Part one:
If the point charge had a negative sign, then it would attract the proton and repel the electron.
If the point charge were positive, then it would attract the electron and repel the proton.
The magnitude would be dependant on the distance between the charge and the particle, the greater the distance between the two, the weaker the effect would be .

Part two:
The acceleration of the proton would be slower than that of of the electron due to its greater mass compared to the electron, regardless of direction. The direction of the proton's acceleration would be dependant on the sign of the charge; if positive then its acceleration would be away from the charge, if negative than the proton would accelerate toward the charge. Similarly(Conversely), the electron would have greater acceleration because of its smaller mass relative to the proton, regardless of direction. If the charge were negative, the electron would accelerate away from the charge. If the charge had a positive sign, then it would attract the electron.

All that looks good to me.

Originally Posted by quikwerk

True, but the question said that they were placed there at different times-- so I assume that to mean that they are not orbiting simultaneously. I had not considered that possibility, however, if that is the case, then how would I answer that? The question gives very little info for me to work with, so I'm feeling a ittle lost....

Yes, I think it's safe to assume that the electron is removed
and the proton placed an equal distance from the charge,
rather than....
they are placed an equal distance from the charge, removed, and again placed an equal distance from the charge.