【GR8677】 The Solution for GRE Physics Practice Test [41-60]

The Solution for GRE Physics Practice Test [41-60]

 

추천글 : 【GRE】 Solution for GRE Physics Practice Test 

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41. Which of the following nuclei has the largest binding energy per nucleon? (Consider the most abundant isotope of each element.)

 

 

 

⑴ answer: C

 

 

 

42. A proton beam is incident on a scatterer 0.1 centimeter thick. The scatterer contains 10²⁰ target nuclei per cubic centimeter. In passing through the scatterer, one proton per incident million is scattered. The scattering cross section is 

 

 

⑴ answer: C

⑵ 10²⁰ × 0.1 × A = 10^-6 ⇔ A = 10^-25 cm² 

 

 

43. Three masses are connected by two springs as shown below. A longitudinal normal mode with frequency 

 

 

is exhibited by 

 

 

⑴ answer: B

⑵ simple harmonic motion 

 

 

44. A uniform stick of length L and mass M lies on a frictionless horizontal surface. A point particle of mass m approaches the stick with speed v on a straight line perpendicular to the stick that intersects the stick at one end, as shown below. After the collision, which is elastic, the particle is at rest. The speed V of the center of mass of the stick after the collision is 

 

 

⑴ answer: A

⑵ momentum conservation : mv = Mv' ⇔ v' = mv / M

 

 

45. Photograph of wavelength λ scatter elastically on free protons initially at rest. The wavelength of the photon scattered at 90° is increased by 

 

 

⑴ answer: D

⑵ Compton scattering

 

 

 

46. A blackbody at temperature T₁ radiates energy at a power level of 10 milliwatts (mW). The same blackbody, when at a temperature 2T₁, radiates energy at a power level of 

 

 

⑴ answer: E

⑵ Stefan-Boltzmann law : P ∝ T⁴ 

 

 

47. The Frank-Hertz experiment and related scattering experiments show that

 

 

⑴ answer: C

⑵ Frank-Hertz experiment

 

GRE Physics (GR1775) #48

 

 

48. A transition in which one photon is radiated by the electron in a hydrogen atom when the electron's wave function changes from ψ₁ to ψ₂ is forbidden if ψ₁ and ψ₂ 

 

 

⑴ answer: D

⑵ electron transition rule

① rule 1. selection rule : Δ ℓ (angular momenta) = ±1

② rule 2. spin conservation law

 

 

49. The Hamiltonian operator in the Schrödinger equation can be formed from the classical Hamiltonian by substituting

 

 

⑴ answer: B

 

 

50. The Hall effect is used in solid-state physics to measure 

 

 

⑴ answer: C

⑵ Hall effect 

 

 

 

51. One feature common to both the Debye theory and the Einstein theory of the specific heat of a crystal composed of N identical atoms is that the 

 

 

⑴ answer: B

 

 

52. A cube has a constant electric potential V on its surface. If there are no charges inside the cube, the potential at the center of the cube is 

 

 

⑴ answer: E

⑵ V_center - V_surface = ∫ -E · dr = 0 (∵ E = 0)

 

 

53. A charged particle oscillates harmonically along the x-axis as shown below. The radiation from the particle is detected at a distant point P, which lies in the xy-plane. The electric field at P is in the 

 

 

⑴ answer: C

⑵ If the particle moves to +x axis, the electric field is towards +x axis (not 100% +x axis according to θ) and the magnetic field is on yz-plane. Also, you may be aware that the signal strength from antenna is the maximum at its vertical position.

 

 

 

54. A dielectric of dielectric constant K is placed in contact with a conductor having surface charge density σ, as shown below. What is the polarization (bound) charge density σ_p on the surface of the dielectric at the interface between the two materials?

 

 

⑴ answer: E 

 

 

55. The mean kinetic energy of electrons in metals at room temperature is usually many times the thermal energy kT. Which of the following can best be used to explain this fact?

 

 

⑴ answer: B

 

 

56. If ψ is a normalized solution of the Schrödinger equation and Q is the operator corresponding to a physical observable x, the quantity ψ*Qψ may be integrated in order to obtain the 

 

 

⑴ answer: C

⑵ For example, Q = 1, ∫ ψ*ψ dx = 1.

 

 

57. Which of the following is an eigenfunction of the linear momentum operator -iℏ∂ / ∂x with a positive eigenvalue ℏk; i.e., an eigenfunction that describes a particle that is moving in free space in the direction of positive x with a precise value of linear momentum?

 

 

⑴ answer: D

 

 

58. In an ordinary hologram, coherent monochromatic light produces a 3-dimensional picture because wave information is recorded for which of the following?

 

 

⑴ answer: B

 

 

59. The dispersion law for a certain type of wave motion is ω = (c²k² + m²)^1/2, where ω is the angular frequency, k is the magnitude of the propagation vector, and c and m are constants. The group velocity of these waves approaches 

 

 

⑴ answer: E

 

 

60. A particle of mass m that moves along the x-axis has potential energy V(x) = a + bx², where a and b are positive constants. Its initial velocity is v₀ at x = 0. It will execute simple harmonic motion with a frequency determined by the value of 

 

 

⑴ answer: C

⑵ simple harmonic motion 

 

 

입력: 2023.10.05 01:43