大学物理双语2012-2013-1月A

一、Choice (4pts*5)

1. Free expansion . A adiabatic

container has two parts connected by

a valve (阀门). The volume of the

two parts is the same ( Fig.1 ). The

left part is filled with ideal gas (diatomic molecule 双原子分子)

with temperature T . When the valve is opened, the gas will expand freely to fill both parts. After the system reach thermal equilibrium, the temperature of the gas is () (a) T (b) 2/T (c) 3/22/T (d) T 2

2 A red star and a blue star, which has higher surface temperature?

(a) The red star (b) The blue star

(c) They have the same surface temperature (d) Unable to determine

3. A particle’s location is measured and specified as being exactly at x = 0, with zero uncertainty in the x direction. How does that location affect the uncertainty of its momentun component in the y direction?

(a) It does not affect it. (b) It makes it infinite. (c) It makes it zero.

4. Unpolarized light passes through two polarizers whose optical axes are in the same direction. The intensity of the emerging light is I 0. If a third polarizer is placed between the polarizers so that its axis is at an angle θ with the other two, the intensity of the emerging light is

(a) zero (b) I 0 (c) I 0 cos 2θ (d) I 0 cos 4θ

5. The following functions may represent the wave motion f (x ,t ) in a one-dimensional elastic medium in terms of position x , time t , and positive

constants A , a , and b . Which function represents a traveling wave moving in the negative x-direction?

(a) ()()bt ax A

t x f +=sin , (b) ()()bt ax A t x f -=sin ,

(c) ()bt ax A t x f cos cos ,= (d) ()bt ax A t x f sin sin ,=

Fig.1

二、Blanks (20pts)

6. (8 pts) A 500 g mass is undergoing simple harmonic oscillation that is described by the following equation for its position x (t ) from equilibrium:

()⎥⎦

⎤⎢⎣⎡+=rad 0.6rad/s 0.6cos )m 50.0()(ππt t x The amplitude A of the oscillation is m. The frequency of the oscillation is Hz. The period T of the oscillation is s. The phase of oscillator at t = 0 s is rad. The maximum speed of the oscillator is m/s .

7. (3pts) When Newton ring apparatus is immersed in a liquid, the diameter of the eighth dark ring decreases form 2.92cm to 2.60cm, the refractive index of the liquid is .

8. (3pts) In single slit diffraction experiment, 680nm light falls on a slit 0.0345mm wide. The angular width of the center diffraction peak is .

9. (3pts) The angular separation of the two components of a double star is 8×10-3 rad and the light from the double stat har a wavelength of 550 nm. According to the Rayleigh criterion, the smallest diameter of a telescope mirror that will resolve the double star is ______ m.

10. (3pts) The De Broglie wavelength of a electron moving at 5.9×106m/s is .

三、Questions (10pts)

11. (5pts) The oceans contains a tremendous amount of thermal energy. Why, in general, it is not possible to put it into useful work.

12. (5pts) what are the two postulates of Einstein ’s Special Theory of Relativity?

四、Problems (50pts)

13. (10pts) For 1 mole O 2 at room temperature (20℃),

(1) what is the average transitional kinetic energy of the molecules?

(2) what is the rms speed of the molecules?

(3) what is the internal energy of the gas?

14. (10pts) The PV diagram of the cycle in Carnot ’s engine is shown in Fig 2. The Carnot cycle has 4 processes:

1 2: Isothermal expansion with addition of heat |Q H |;