30. A tube open at one end and closed at the other end produces sound having a fundamental frequency of 350 Hz. If you now open the closed end, the fundamental frequency becomes
(A) 87.5 Hz.
(B) 175 Hz.
(C) 350 Hz.
(D) 700 Hz.
(E) 1400 Hz.

26. At what rate is thermal energy being generated in the 2R-resistor when ε = 12 V and R = 3.0 Ω? (A)12 W (B) 24 W (C) 6.0 W (D)3.0 W (E)1.5 W

27. A charged capacitor stores energy U, Without connecting this capacitor to anything, dielectric having dielectric constant K is now inserted between the plates of the capacitor, completely filling the space between them. How much energy does the capacitor now store? (A)2KU (B)KU (C)U (D)U/K (E)U/(2K)

28. As shown in the figure, a wire and a 10-Ω resistor are used to form a circuit in the shape of a square, 20 cm by 20 cm. A uniform but nonsteady magnetic field is directed into the plane of the circuit. The magnitude of the magnetic field is decreased from 1.50 T to 0.50 T in a time interval of 63 ms. The average induced current and its direction through the resistor, in this time interval, are closest to  (A) 63 mA, from b to a. (B)38 mA, from b to a. (C) 63 mA, from a to b. (D) 38 mA, from a to b. (E) 95 mA, from a to b.

29. A transverse wave traveling along a string transports energy at a rate r. If we want to double this rate, we could (A) increase the amplitude of the wave by a factor of 8. (B) increase the amplitude of the wave by a factor of 4. (C) increase the amplitude of the wave by a factor of 2. (D) increase the amplitude by a factor of √2. (E) increase the amplitude by a factor of √8.

31. A solid nonconducting sphere of radius R carries a charge Q distributed uniformly throughout its volume. At a certain distance r1 (r1 ＜ R) from the center of the sphere, the electric field has magnitude E. If the same charge Q were distributed uniformly throughout a sphere of radius 2R, the magnitude of the electric field at the same distance r1 from the center would be equal to (A) E/8. (B) E/2.(C) 2E.(D) 8E. (E) E.

32. Determine the energy stored in C2 when C1 = 15 MF, C2 = 10 MF, C3 = 20 uF, and V0 = 18 V. Xx (A)0.72 mJ (B)0.32 mJ (C)0.50 mJ (D)0.18 m.J (E)1.60 mJ

33. A charge per unit length given by λ(x) = bx, where b = 12 nC/m2, is distributed along the x axis from x = +9.0 cm to x = +16 cm. If the electric potential at infinity is taken to be zero, what is the electric potential at the point P on the y axis at y = 12 cm? (A)5.4 V (B)7.2 V (C)9.0 V (D)9.9 V (E) 16 V

34. A 16-nC charge is distributed uniformly along the x axis from x = 0 to x = 4 m. Which of the following integrals is correct for the magnitude (in N/C) of the electric field at x = +10 m on the x axis?  (A)(B)(C)(D)

複選題35. The electric field in the region of space shown is given by ㆍ N/C where y is in m. What is the magnitude of the electric flux through the top face of the cube shown?  (AB) 90 N ㆍm2/C (AC) 6.0 N ㆍ m2/C (AD)54 Nㆍ m2C (AE)12 Nㆍ m2/C (BC) 126Nㆍ m2/C (BD)一律送分

36. A charge per unit length given by 1(x) = bx, where b = 12 nC/m2, is distributed along the x axis from x= t9.0 cm to x= +16 cm. If the electric potential at infinity is taken to be zero, what is the electric potential at the point P on the y axis at y = 12 cm? (A)5.4 V (B)7.2 V (C)9.0 V (D)9.9 V (E) 16 V