Phy 132 - Assignment 2
A. 1. a. Equal. From ΔV = ⃑⃑⃑
= – E cos s, there is no difference in V if
you move across the field (cos 90° = 0). It’s only how much you move along
the field (cos 0 = 1) that matters. From A to B or A to C, it’s the same distance
horizontally.
b. More. From the same equation, ΔVBC = 0 because cos 90° = 0.
c. A . Electric field lines point from high to low potential, and they point from
A toward B and C. (If it was a gravitational field, the field lines would show
which way water runs; high to low in the steepest direction.)
2.
B. 1. U = UAB + UAC + UBC
Where U of each pair =
Since all masses and distances are the same,
UAB = UAC = UBC.
So, U = 3UAB = [
= – 1.67 x 10-9 J
]
2.
C. 1. The proton. One way to see this is to remember that field lines point from
+ to -, and to also remember that they point “downhill;” that is, toward lower
potential. So, + is at the higher potential.
2.
D. 1. Stays the same. Potential is a property of the field, and the field did not
change. (If you were looking at V = U/q, U goes up by the same factor as q.)
2.
E. 1. Any direction perpendicular to the field, such as
y or z. Work = ⃑
= F cosθ s. You want a
direction where cosθ = 0.
2.
F. 1. Remember to treat V as a scalar. There is no direction; just add numbers.
Remember to treat ⃑ as a vector. Think in terms of arrows on a picture.
(Formulas only tell you how long the arrows are.) A positive charge’s field
points away from it and a negative charge’s field points toward it, so
2.