# ｔ＝ 98 學年度第 2 學期物理 Chap15 作業

```班級:光電一乙

98 學年度第 2 學期物理 Chap15 作業
1. Four point charges are situated at the corners of a square with sides of length
a, as in Figure 1. Find the expression for the resultant force on the positive
charge q.

2. (a) Determine the electric field strength at a point 1.00 cm to the left of the
middle charge shown in Figure 2. (b) If a charge of −2.00 μC is placed at this
point, what are the magnitude and direction of the force on it?
(a)
(b)
Ｆ＝Ｅｑ
＝
＝－40Ｎ（40N 向左）
Figure 2
3. In Figure 3, determine the point (other than infinity) at which the total electric
field is zero.
（先經過討論
=&gt;

=&gt;6
=&gt;3.5
(上一式乘 2)=&gt;7
r=
=左邊 1.82m(負不合)
r
Figure3
4. A point charge of +5.00 μC is located at the center of a sphere with a radius of
12.0 cm. Determine the electric flux through the surface of the sphere.
5. A small 2.00-g plastic ball is suspended by a 20.0-cm-long string in a uniform
electric field, as shown in Figure 4. If the ball is in equilibrium when the string
makes a 15.0&deg; angle with the vertical as indicated, what is the net charge on
the ball?
m=2
E=1
g=9.8
T 為繩之張力
=&gt;T
T=2.031
N
Figure 4
=&gt;T
=&gt;5.256
q=5.256
=5.256
```