Question

Electric fields and forces?? Please help?

Answer 1

Why isn't is A? Why is it going in a straight line?

Answer 2

The answer is B. But I don't get why.

Answer 3

Because it is attracted to the plate by a 1/(r^2) law and it is attracted to the earth by gravity which is also 1/(r^2) law. (i.e. its acceleration is the same down due to gravity as it is to the left by the Coulomb force) The equal acceleration in both directions gives a straight line.

Answer 4

But I haven't really done this law yet. Which law is it? Is there any simpler explanation?

Answer 5

Which law haven't you done yet? Newtonian gravity attraction is G(m1*m2)/R^2. The Coulomb force is Kc(q1*q2)/R^2. They have exactly the same form and as a result the particle will undergo the same acceleration due to both. At first the particle falls a little due to gravity and will move a little left due to electrical attraction. A little later it will be falling faster since gravity's attraction will still be applying a force (F=ma). But at the same time it will be moving to the left faster and faster too since the Coulomb force grows exponentially with distance. The point is the acceleration of both forces is exponential. Their velocities will increase at the same rate so the trajectory is linear. If things fell at a constant rate in a gravitational field, then "A" would be the right answer. Since they speed up in a gravitational field (as well as an electric field) they end up going in a straight line.

Answer 6

Oh, I understand now! Yeah, I did do those laws, just didn't know how to apply. Thanks!