The Solution for GRE Physics Practice Test [41-60]
추천글 : 【GRE】 Solution for GRE Physics Practice Test
41. In an experimental observation of the photoelectric effect, the stopping potential was plotted versus the light frequency, as shown in the figure below. The best straight line was fitted to the experimental points. Which of the following gives the slope of the line? (The work function of the metal is ϕ.)
⑴ answer: B
⑵ E = eV = hf - ϕ ⇔ ΔV / Δf = h / e
42. Two sinusoidal waveforms of the same frequency are displayed on an oscilloscope screen, as indicated below. The horizontal sweep of the oscilloscope is set to 100 ns/cm and the vertical gains of channels 1 and 2 are each set to 2V/cm. The zero-voltage level of each channel is given at the right in the figure. The phase difference between the two waveforms is most nearly
⑴ answer: E
⑵ Δϕ = 4 bins / 6 bins × 360° = 240° ≡ 120° (mod 360°)
43. In the diamond structure of elemental carbon, the nearest neighbor of each C atom lie at the corners of a
⑴ answer: D
⑵ diamond : tetrahedron
⑶ graphite : hexagon
44. According to the BCS theory, the attraction between Cooper pairs in a superconductor is due to
⑴ answer: D
45. During a hurricane, a 1,200 Hz warning siren on the town hall sounds. The wind is blowing at 55 m/s in a direction from the siren toward a person 1 km away. With what frequency does the sound wave reach the person? (The speed of sound in air is 330 m/s.)
⑴ answer: C
⑵ The same frequency is calculated when the observer and the source moves backward by 55 m/s without wind.
⑶ f = f0 × (330 - 55) / (330 - 55) = f0 = 1200 Hz
46. Sound waves moving at 350 m/s diffract out of a speaker enclosure with an opening that is a long rectangular slit 0.14 m across. At about what frequency will the sound first disappear at an angle of 45° from the normal to the speaker face?
⑴ answer: D
⑵ d sin θ = 0.14 / √2 = λ = 350 / f ⇔ f = 3,536 Hz
47. An organ pipe, closed at one end and open at the other, is designed to have a fundamental frequency of C (131 Hz). What is the frequency of the next higher harmonic for this pipe?
⑴ answer: D
⑵ λn = 4L / (2n-1) = v / fn ⇔ fn = v / 4L × (2n-1)
48. For the logic circuit shown below, which of the following Boolean statements gives the output E in terms of inputs A, B, C, and D?
⑴ answer: C
⑵ combinational logic circuit : ° means "NOT".
49. Which of the following lasers utilizes transitions that involve the energy levels of free atoms?
⑴ answer: D
50. Which of the following expressions is proportional to the total energy for the levels of a one-electron Bohr atom? (m is the reduced mass, Z is the number of protons in the nucleus, -e is the charge on the electron, and n is the principal quantum number.)
⑴ answer: C
⑵ velocity
⑶ radius
⑷ energy
51. True statements about the absorption and emission of energy by an atom include which of the following?
⑴ answer: D
⑵ Ⅲ. As the temperature increases, the relativistic effects of atomic motion can cause differences in the absorption and emission spectra.
52. X rays of wavelength λ = 0.250 nm are incident on the face of a crystal at angle θ, measured from the crystal surface. The smallest angle that yields an intense reflected beam is θ = 14.5°. Which of the following gives the value of the interplanar spacing d? (sin 14.5° ≈ 1/4)
⑴ answer: C
⑵ Bragg's law : 2d sin θ = nλ = 1 × 0.250 nm
⑶ ∴ d = 0.500 nm
53. Astronomers observe two separate solar systems, each consisting of a planet orbiting a sun. The two orbits are circular and have the same radius R. It is determined that the planets have angular momenta of the same magnitude L about their suns, and that the orbital periods are in the ratio of three to one; T1 = 3T2. The ratio m1 / m2 of the masses of the two planets is
⑴ answer: D
⑵ L = Iω = mR2ω = 2π mR2 / T = constant
54. If the Sun were suddenly replaced by a black hole of the same mass, it would have a Schwarzschild radius of 3,000 m. What effect, if any, would this change have one the orbits of the planets?
⑴ answer: E
⑵ Schwarzschild radius, also called gravitational radius, the radius below which the gravitational attraction between the particles of a body must cause it to undergo irreversible gravitational collapse.
55. A distant galaxy is observed to have its hydrogen-β line shifted to a wavelength of 580 nm, away from the laboratory value of 434 nm. Which of the following gives the approximate velocity of recession of the distant galaxy? (Note: 580/434 ≈ 4/3)
⑴ answer: A
⑵ red shift due to cosmological Doppler effect
56. A small plane can fly at a speed of 200 km/h in still air. A 30 km/h wind is blowing from west to east. How much time is required for the plane to fly 500 km due north?
⑴ answer: D
⑵ T = 500 / √(2002 - 302) = 50 / √391 (h)
57. Each of the figures below shows blocks of mass 2m and m acted on by an external horizontal force F. For each figure, which of the following statements about the magnitude of the force that one block exerts on the other (F12) is correct? (Assume that the surface on which the blocks move is frictionless.)
⑴ answer: B
58. In the figure below, A has mass mA = 25 kg and block B has mass mB = 10 kg. Both blocks move with constant acceleration a = 2 m/s2 to the right, and the coefficient of static friction between the two blocks is μs = 0.8. The static frictional force acting between the blocks is
⑴ answer: A
⑵ f = ma = 10 × 2 = 20 N
59. A simple pendulum of length ℓ is suspended from the ceiling of an elevator that is accelerating upward with constant acceleration a. For small oscillations, the period, T, of the pendulum is
⑴ answer: C
⑵ simple pendulum
⑶ accelerating frame : g → g + a
60. Three long, straight wires in the xz-plane, each carrying current I, cross at the origin of coordinates, as shown in the figure below. Let x̂, ŷ, and ẑ denote the unit vectors in the x-, y-, and z-directions, respectively. The magnetic field B as a function of x, with y = 0 and z = 0, is
⑴ answer: C
⑵ Btot = μ0I / 2πx + μ0I / 2π(x / √ 2) + μ0I / 2π(x / √ 2)
입력: 2023.10.07 13:47
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