Version One – Homework 1 – Juyang Huang – 24018 – Jan 16 ...

Version One – Homework 1 – Juyang Huang – 24018 – Jan 16, 2008 16
Explanation:
keywords:
The total electrostatic energy of the system
is the sum of the electrostatic energies
between each pair of charges:
U = U 12 + U 23 + U 31
The electrostatic energy between the charges
q i and q j is given by
U ij =
q i q j
4 π ɛ 0 r
−Q
where r is the distance between the charges,
so, since k e = 1 ,
4 π ɛ 0
]
U = k e a
[q 1 q 2 + q 2 q 3 + q 3 q 1
= ( 8.98755 × 10 9 N · m 2 /C 2)
[
× (0.2 m) (1.5 × 10 −6 C) (3 × 10 −6 C)
+ (3 × 10 −6 C) (−5 × 10 −6 C)
]
+ (−5 × 10 −6 C) (1.5 × 10 −6 C)
= −0.80888 J .
1. No charge flows.
keywords:
Moving a Charge
25:02, trigonometry, numeric, > 1 min, normal.
035 (part 1 of 1) 10 points
It takes 120 J of work to move 1 C of charge
from a positive plate to a negative plate.
What voltage difference exists between the
plates
Correct answer: 120 V.
Explanation:
Let : W = 120 J and
q = 1 C .
The voltage difference is
V = W q = 120 J
1 C = 120 V .
AP B 1993 MC 70
25:03, trigonometry, multiple choice, < 1 min,
fixed.
036 (part 1 of 1) 10 points
Two negatively charged spheres with different
radii are shown in the figure below.
−Q
The two conductors are now conneted by a
wire.
Which of the following occurs when the two
spheres are connected with a conducting wire
2. Negative charge flows from the larger
sphere to the smaller sphere until the electric
field at the surface of each sphere is the
same.
3. Negative charge flows from the larger
sphere to the smaller sphere until the electric
potential of each sphere is the same.
4. Negative charge flows from the smaller
sphere to the larger sphere until the electric
field at the surface of each sphere is the
same.
5. Negative charge flows from the smaller
sphere to the larger sphere until the electric
potential of each sphere is the same. correct
Explanation:
When the wire is connected, charge will flow
until each surface is at the same potential.
When disconnected the potential of each