The uniform field: the same everywhere

Where is the field stronger?

Most fields in this topic change from place to place: stronger here, a new direction there. One field does not change at all. Between two oppositely charged parallel plates, the field keeps the same strength and the same direction everywhere, and its drawing shows that at a glance.

The drawings come first; the name comes after.

Here are three drawn fields, one after another. At each place, the lines show the direction of the force on a small probe placed there.

This field is not the same everywhere. Its lines point different ways in different parts of the field.

This field is the same everywhere. Its lines are straight and parallel, with even gaps, all pointing one way: same direction and same spacing, so same strength, from point to point.

This field is not the same everywhere. Its lines curve, and their gaps change from place to place.

Only the second field has the same strength and the same direction at every point. A field with the same strength and direction at every point is called a uniform field.

In one field, the force on a given object keeps the same strength and direction at every point. Is the field uniform?

A uniform field is drawn as parallel, evenly spaced field lines. That is the drawing's way of promising no change from point to point.

In another field, the force direction on a given object swings around from point to point. Is that field uniform?

The field between two oppositely charged parallel plates is the classic uniform field: every line straight, parallel, evenly gapped, pointing from the positive plate to the negative plate.

A field with the same strength and direction at every point is called a ___ field. Type the missing word.

Your turn

Which drawing shows a uniform field?

In a uniform field, how does the force on a given object compare from place to place?

The drawn field is uniform. A ball near the top of the region and the same ball near the bottom each feel the field's force. Compare the two forces.