[試題] 清華大學 94下 普物期中考(第一次)
課程名稱: 普通物理A
課程性質:
課程教師: 余怡德
開課系所: 物理系
考試時間: 95.3.30
1.Two identical conducting spheres.fixed in place,attract each other with an
electrostatic force of 0.432 N when their center to center separation is
50.0 cm.The spheres are then connected by a thin conducting wire.When the
wire is removed,the spheres repel each with an electrostatic force of 0.144 N
Of the initial charges on the spheres,with a positive net charge,what was
(a)the negative charge on one of them and (b)the positive charge on the other
2.The charges and coordinates of two charged particles held fixed in a xy plane
are q_1 = 6.0(μC),(3.5cm,0.5cm),and q_2 = -8.0(μC),(-2.0cm,1.5cm).Find the
(a) x and (b) y coordinates should a third particles of charge q_3 = 8.0(μC)
be placed such that the net electrostatic force on particle 3 due to particle
1 and 2 is zero?
3.In the figure,two tiny conducting balls of identical mass m and identical
charge q hang from nonconducting threads of length L.Assuming that θ is so
small that tanθ can be replaced by its approximate equal,sinθ.What will be
the new separation if I increase (a) both charges from q to 4q,or (b) both
masses from m to 4m?
figure: ╴╴╴╴╴╴╴╴╴╴╴
╱╲
╱ ｜ ╲
L ╱ θ｜θ ╲ L
╱ ｜ ╲
╱ ｜ ╲
○ ○
q |--------x---------|
4.An electric quadrupole is shown below.It consists of two dipoles with dipole
moments that are equal in magnitude but opposite in direction.Use R to denote
the value of the electric field on the axis of the quadrupole for a point P
a distance z from its center (assume z >> d).By what factor is the magnitude
of electric field multiplied if I (a) triple the separation d to 3d,or (b)
measure it at a distance 3z?
figure:
|--d--| |--d--|
○ ●● ○ ☆P
q -q -q q
|-------------z-------------|
5.Figure 1 shows a nonconducting rod with a uniformly distributed charge Q.
The rod forms a three-quarter-cirlce with radius R and produces an eletric
field of magnitude E at its center of curvature P.If the arc is collapsed to
a point at distance R from P (figure 2),by what factor is the magnitude of
the electric field at P multiple?
Figure:很難畫...Orz
不過不看圖應該也作得出來 :p
6.Charge Q is distributed uniformly on the surface of a CD-like disk with inner
radius of R/2 and outer radius 2R,What are the (a) electric field and (b)
electric potential at a point which is along the central perpendicular axis
of the disk and at distance 2R from the disk.
7.A uniformly upward electric field E is set up between two parallel plates
with uniform charge densities σ= 2(C/m^2) on the lower plate and -σ on the
upper plate.(a) What is magnitude of this electric field? If the plates have
length L = 10.0(cm) and separation d = 2.00(cm).A electron is then shot
between the plates from the left edge of the lower plate.The initial velocity
v_0 of the election makes a angle θ= 60(度) with the lower plate.(b) What is
the minimum magnitude of v_0 required for the electron to reach the upper
plate? (c) At this minimum velocity,how far horizontally from the left edge
will the electron strike?
figure:
╴╴╴╴╴╴╴╴╴╴╴╴╴╴╴
↑
v_0 ↑E d
↗
╱θ ↓
￣￣￣￣￣￣￣￣￣￣￣￣￣￣￣
|---------------L--------------|
8.A Gaussian surface in the shape of a cube with edge length 4.0(m).What are
(a) the net flux through the surface and (b) the net charge enclosed by the
surface if E = (-4.0 , 6.0+3.0y , 0) N/C with y in meters.
9.A very large nonconducting slab of thickness d = 12.0(mm) and uniform volume
charge density ρ= 5.80 x 10^(-15) C/m^3.The origin of an x axis is at the
slab's center.What is the magnitude of the slab's electric field at an x
coordinate of (a) 2.00(mm),(b)26.0(mm)?
10.A nonconducting spherical shell of inner radius a = 2.00(cm) and outer
radius b = 2.40(cm) has(with its thickness) a positive bolume charge density
ρ = A/r,where A is a constant and r is the distance from the center of the
shell.In addition,a small ball of charge q = 55.0 x 10^(-15) C is located
at that center.What value should A have if the electric field in the shell
(a < r < b) is to be uniform.
= =
11.Two isolated,concentric,conducting spherical shells have radii R_1 = 0.50(m)
and R_2 = 1.00(m),uniform charge q_1 = 6.00(μC) and q_2 = 3.00(μC),and
negligible thicknesses.With the electric potential V = 0 at infinity,what
is V at (a) r = 4.00(m),(b) r = 7.00(m)?
13.A 20.0(V) battery is connected across capacitors of capacitances
C_1 = C_2 = 4.0(μF) and C_3 = C_5 = 2C_2 = 2C_4 = 4.0(μF).What are (a) the
equivalent capacitance of the capacitors and (b) the charge stores in
capacitor 2?
figure: C_2
┌───┬─────┬─││──┐
│ │ ─ │
│ ─ C_4 ─ C_5 │
---- ─ │ │
V ─ │ ─ │
│ │ ─ C_3 │
│ ├─────┼─────┘
│ │ │
│ ─ C_6 │
│ ─ │
│ │ │
└───┴──││─┘
C_1
14.A parallel-plate capacitor of plate area A = 10.5(cm^2) and plate separation
2d = 9.00(mm).The left half of gap is filled with material of dielectric
constant κ_1 = 21.0;the top of the right half is filled with material of
dielectric constant κ_2 = 42;the bottom of the right half is filled with
dielectric constant κ_3 = 58.0.What is the capacitance?
15.Current is set up through a truncated right circular cone of resistivity
600(Ω*m),left radius a = 2.00(mm),right radius b = 2.30(mm),and the length
L = 1.94(cm).Assume that the current density is uniform across any cross
section taken perpendicular to the length.What is the resistance of the cone?
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※ 編輯: Serge45 來自: 61.231.30.102 (07/05 12:20)
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