Before we begin looking into how transistors work, it would be helpful to revisit the relationship between the distribution of charge and electric field.
Let's assume we have an infinitely large two dimensional plane sheet
of charge.
Click on the plane to positively charge it.
In practice, the plane does not need to be infinite. If we only look
at the points in space close to the plane, (i.e. x much smaller than
the plane size in y and z directions) we can consider the plane
infinite.
Note that charge is evenly distributed on the plane and the finite
number of + signs is for representation purposes. In reality, the
number of charged particles is many, many orders of magnitude
larger.
Can you explain why the electric field is perpendicular to the
plane? (Hint: Think about symmetry)
What happens if we change the charge density?
(Use the slidebar)
What happens if you negatively charge the plane?
Let’s look at what happens when we put two sheets of opposite
charges together. This effect is called screening.
You can click and drag to move the negatively charged sheet...
Use the buttons below to show the screening effect or toggle the
arrows.
The charge density in the two plane sheets may not always match exactly. Let’s see what happens in that case.
What if we add an additional plane sheet of negative charge such that the total negative charges become equal to the positive charges?
The full screening may happen via multiple sheets of charge of
varying densities.
Use the slider to gradually move negative charges left and right.
What if the negative charges are evenly distributed within a given volume? One can consider this as an extreme case of having a large number of plane sheets of negative charge.
Use the slider to change the width of the volume.