Phy 132 – Assignment 1
A.

B. By definition, E ’s direction
is that of the force on a positive test charge.

Therefore, in each case, E points toward the origin, since opposites attract.
The question doesn’t specifically ask for component form, so it would be ok to
just leave it in terms of magnitude and direction. Or, you could keep going:
C.
D.
E. 1. a. The forces are the same size. F = qE (from E = F/q). The electron’s
charge is the same size as to the proton’s, and both are in identical E’s.
b. The electron has a larger acceleration. a = F/m (from F = ma). Both forces
are the same size, but the electron has less mass.
2.
F.1.
2. F
q1 q 2
1
4
0
r
2
8.988x10 9
(1.60 x10
19
)(1.60 x10
(3.80 x10
10 2
)
19
)
1.59 x10 9 N
(Repulsive because the charges are the same.)
3. F = ma = (9.110 x 10-31 kg)(1.8 x 1016 m/s2) = 1.640 x 10-14 N
E = F/q = (1.64 x 10-14 N)/(1.602 x 10-19 ) = 1.02 x 105 N/C
(I would accept it if you used –1.6 x 10-19 for q, giving a negative answer.
However, I took the question to be asking for just the magnitude of the field,
which is a positive number. The minus only matters if you’re interested in the
direction.)