課程名稱︰普通物理學甲下
課程性質︰系定必修
課程教師︰石明豐
開課學院：電資學院
開課系所︰電機系
考試日期（年月日）︰2007.4.26
考試時限（分鐘）：110
是否需發放獎勵金：是，謝謝
（如未明確表示，則不予發放）
試題 :
(5 pts for each of 1-14)
1. A 20-m-long spacecraft (as measured by a pilot on the spacecraft) travels
at a constant speed past a 40-m-long space dock (as measured by a worker
on the dock). The worker measures the length of the spacecraft as it
passes and finds it to be 18m long. The pilot measures the length of the
dock as
(A) 36m (B) 38m (C) 42m (D) 44m (E) 48m
2. Following 1. The dock worker observes a clock on the spacecraft for one
minute (according to a clock on the dock). The clock on the spacecraft,
however, will show an elapsed time of
(A) 48s (B) 54s (C) 60s (D) 67s (E) 78s
3. Two events occur on the x axis separated in time by Δt and in space by
Δx. A reference trame, traveling at less than the speed of light, in
which the two events occur at the same time: This reference frame
(A) exists no matter what values of Δt and Δx.
(B) exists only if Δx/Δt < c.
(C) exists only if Δx/Δt > c.
(D) exists only if Δx/Δt = c.
(E) does not exist under any condition.
4. A particle with zero mass and energy E carries momentum:
(A) Ec (B) Ec^2 (C) (Ec)^1/2 (D) E/c (E) E/c^2
5. The figure shows the electric field lines around an electric dipole.
Which of the arrows best represents the electric field at poiny P?
(A)↑ (B)↖ (C)↖(比前一個彎) (D)↗ (E)↙
6. The torque exerted by an electric field on a dipole is:
(A) ||E and ⊥P (B) ||E and ||P (C) ⊥E and ⊥P (D) ⊥E and ||P
(E) none of the above.
7. Consider Gauss' law:∮E‧dA = q/ε0. Which of the following is true?
(A) E must be the electric filed due to the enclosed charge.
(B) If q=0, then E=0 everywhere on the Gaussian surface.
(C) If the charge inside consists of only electric dipole, then the
integral is zero.
(D) On the surface E||dA.
(E) If a charge is placed outside the surface, then it cannot affect
E at any point on the surface.
8. An electric dipole parallel to x axis located at the origin experiences
an electrostatic force directed along the x axis. One can conclude that
at the origin
(A) V≠0 (B) aV/ax≠0 (C) a^2 V/ax^2 ≠0
(D) Two of A,B or C must be true. (E) All three must be true.
(PS.B和C選項的a是偏微分的符號)
9. The current is zero in a conductor when no potential difference is applied
because:
(A) the electrons are not moving
(B) the electrons are not moving fast enough
(C) equal numbers of electrons and protons are moving together
(D) for every electron with a given velocity, there is another with a
velocity of equal magnitude and opposite direction
(E) if not so, the Ohm's law would not be valid.
10. Consider a parallel-plate capacitor originally with charge q0 and
capacitance C0. There is an electrostatic force of magnitude F0 between
the plates, and the capacitor has a stored energy U0. The dielectric
slab with κe > 1 is inserted between the plates. Which quantities
increase? (choose all that are correct)
(A) q (B) C (C) △V (D) F (E) U.
11. Suppose the current charging a capacitor is kept constant. Which graph
correctly gives the potential difference V across the capacitor as a
function of time?
12. If the field is not uniform; it is stronger at the top than at the bottom
of the page. What is the direction of the torque on the current loop?
(A) Into the page (B) Out of the page (C) Up the page (D) Down the page
(E) The net force is zero.
13. A hollow cylinderical conductor (inner radius = a, outer radius = b)
carries a current i uniformly spread over its cross section. Which graph
below correctly gives B as a function of the distance r from the cylinder?
14. A rectangular loop of wire resistance R moves through a constant uniform
magnetic field B, perpendicular to the loop. If L is the length of each
side, the force that must applied by a person to keep the loop moving
with constant velocity v is:
(A) 0 (B) BLv (C) BLv/R (D) v(BL)^2/R (E) (BLV)^2/R
15. Estimate the number you answer correctly for Problems 1 to 14. 5 points
for bingo. -5 points if erring by more than 1. 0 points if you choose not
to estimate or you mistake by just 1.
(15 pts for each of 16 and 17)
16. A spherical region carries a uniform charge per unit volume ρ. A
spherical cavity is created in the sphere, the vector from the center of
the sphere to the center of the cavity is a. What is the electric field
at points ( r from the center of the cavity) within the cavity?
17. An electronicmagnetic brake consists of a disk of conductivity σ and
thickness t rotating about an axis through its center with a magnetic
field B applied perpendicular to the plate of the disk over a small area
a^2. If the area a^2 is at a distance r from the axis. Find the torque
tending to slow down the disk at the instant its angular velocity equals
ω.
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 140.112.252.89