Video: Understanding Electric Fields

The diagram shows the electric field produced by a negatively charged metal sphere. If a positively charged particle is placed at the point P, in which direction will it move?

02:10

Video Transcript

The diagram shows the electric field produced by a negatively charged metal sphere. If a positively charged particle is placed at the point P, in which direction will it move?

Looking at the diagram, we see the negatively charged metal sphere. That’s the blue circle at the center. Because the sphere has a net electric charge, that means it creates an electric field around itself. And the representation of that field is these hashed filed lines. Along with the field lines, we see three points that are marked out, point P, point R, and point S over here. We want to know if we take a positively charged particle and we locate it at point P, so right there, in which direction will that particle move.

To figure this out, there are two different ways that we could look at this situation. One is to consider the fact that we have a positively charged particle and a negatively charged metal sphere. This means we can recall how, unlike electric charges, positive and negative interact with one another.

If we have two electric charges, one positive and the other negative, then the force between them will be attractive. That is, the positive charge will be drawn towards the negative. And the negative charge will be drawn towards the positive. Going back to our diagram, we can say then that this positive particle will be drawn directly towards the negative metal sphere, along this field line. That’s one way to look at the question. And there’s a second approach we could take as well.

Notice that, on all these electric field lines, there are arrows indicating the direction of the field. We can see that this electric field is pointed inward straight towards the center of this metal sphere. Knowing this, we can recall a fact about electric field direction. We can remember that electric field direction, the arrows on the electric field lines, show which way a positive charge would move if it was in the electric field.

Of course in our case, we indeed have a positive charge in this field. And as we saw that all the field lines point in towards the metal sphere and that this positive charge is along the field line, this confirms that indeed this positive charge will be drawn in this direction along the electric field line toward the metal sphere. And that’s our final answer for which way the positively charged particle will move.

It will move towards the negatively charged metal sphere.

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