SOLUTIONS – HW2
Q216) The net charge on a conductor is the sum over all positive and negative
charges. It is zero if positive and negative charges are equal.
Free charges are charges that can move inside the conductor. The conductors itself,
though, is still electrically neutral.
Q2114) Large test charges would distort the field we are trying to measure.
Q2115) Positive test charges feel a force along the field lines (from plus to minus).
We can of course also use a negative test charge, but we have to keep in mind that
for a negative test charge, the force is opposite to the field lines; we would thus
measure –
E
.
Q2117) We will put the origin at the position of the positive charge, thus the two
charges are at (0,0) and (12.0cm,0).
The total electric field is then given by the contributions from the two point charges.
We expect the field to be strongest to the right and weakest to the left, with
intermediate and equal values at top and bottom (due to symmetry). As the electric
field decreases with the distance squared, we also expect that the field will be mostly
dominated by the positive charge.
Let us first calculate the magnitude of both contributions for a test charge 2.5 cm
from the positive charge (this is in addition to what is asked in the homework set):
The contribution from the positive charge is the same for all four positions (left = (
2.5 cm,0), right = (+2.5 cm,0), top = (0, +2.5 cm), and bottom =(0,2.5cm), as the
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '08
 Jordan
 Charge, Electric charge

Click to edit the document details