【GR1776】 The Solution for GRE Physics Practice Test [01-20]

The Solution for GRE Physics Practice Test [01-20]

 

추천글 : 【GRE】 Solution for GRE Physics Practice Test 

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1. A net force F_A acts on object A, and a net force F_B acts on object B. The mass of object B is twice the mass of object A, and the acceleration of object B is twice that of object A. Which of the following is true of forces F_A and F_B?

 

 

⑴ answer: E

⑵ F_B = m_Ba_B = (2m_A)(2a_A) = 4m_Aa_A = 4F_A 

 

 

2. Two objects sliding on a frictionless surface, as represented below, collide and stick together. How much kinetic energy is converted to heat during the collison?

 

 

⑴ answer: E

⑵ final state : 1.5 kg, 2/3 m/s upward, 2/3 m/s right

⑶ converted energy 

 

 

 

3. Two simple pendulums A and B consist of identical masses suspended from strings of length L_A and L_B, respectively. The two pendulums oscillate in equal gravitational fields. If the period of pendulum B is twice the period of pendulum A, which of the following is true of the lengths of the two pendulums?

 

 

⑴ answer: E

⑵ period of pendulum

 

 

⑶ 2π √(L_B / g) = 2 × 2π √(L_A / g) ⇔ L_B = 4 L_A 

 

 

4. For the circuit shown in the figure below, what is the current i through the 2 Ω resistor?

 

 

⑴ answer: B

⑵ total resistor = 1 + (1/1 + 1/2)^-1 = 5/3 Ω

⑶ total current = 12 A

⑷ i = 12 × 1/(2+1) = 4 A

 

 

5. By definition, the electric displacement current through a surface S is proportional to the  

 

 

⑴ answer: E

⑵ there 4 kinds of currents: drift current, diffusion current, polarizing current, and displacement current

 

 

6. The electric field of a plane electromagnetic wave of wave number k and angular frequency ω is given by E = E₀ (e_x + e_y) sin (kz - ωt). Which of the following gives the direction of the associated magnetic field B ? 

 

 

⑴ answer: B

⑵ point 1. B is placed on x-y plane

⑶ point 2. B is perpendicular to E 

⑷ point 3. Poynting vector equation can indicate the direction of B 

 

 

 

7. Which of the following is true about any system that undergoes a reversible thermodynamic process?

 

 

⑴ answer: C

⑵ A reversible process is a process in which the total entropy change is zero.

 

 

8. For which of the following thermodynamic processes is the increase in the internal energy of an ideal gas equal to the heat added to gas?

 

 

⑴ answer: B

⑵ Q = U + W can be equal to U if and only if W = ∫ P dV = 0, thus constant volume is related. 

 

 

9. The root-mean-square speed of molecules in an ideal gas of molar mass M at temperature T is  

 

 

⑴ answer: D

⑵ proof

 

 

 

10. Light of variable frequency ν shines on the metal surface of a photoelectric tube. Einstein's theory of the photoelectric effect predicts that the 

 

 

⑴ answer: D

⑵ maximum kinetic energy of electron = | eV | - Φ = h(f - f_threshold) (cf. Φ : work function)

 

 

11. Characteristic X rays, appearing as sharp lines on a continuous background, are produced when high-energy electrons bombard a metal target. Which of the following processes results in the characteristic X rays?

 

 

⑴ answer: C

⑵ the principle of characteristic X rays

 

출처 : 이미지 클릭

Figure. 1. the principle of characteristic X rays

 

 

12. A single-electron atom has the electron in the ℓ = 2 state. The number of allowed values of the quantum number m_ℓ is 

 

 

⑴ answer: E

⑵ orbital theory : m_ℓ = -ℓ, -ℓ+1, ..., 0, ..., ℓ-1, ℓ. Thus, the possible number of m_ℓ is (2ℓ + 1).

 

 

13. A particle of mass m is confined inside a one-dimensional box (infinite square wall) of length a. The particle's ground state energy is which of the following?

 

 

⑴ answer: D

⑵ particle in a box 

 

 

 

14. The Planck length is the only combination of the factors G (Newton's gravitational constant), ℏ (Planck's constant / 2π), and c (the speed of light) that has units of length. Which of the following gives the Planck length? 

 

 

⑴ answer: A

⑵ dimension analysis : [ℏG / c3] = [L²T^-1M] [L³T^-2M^-1] [L^-3 T³] = [L²] 

 

 

15. The speed of light inside of a nonmagnetic dielectric material with a dielectric constant of 4.0 is 

 

 

⑴ answer: C

⑵ how to derive the speed of light 

 

 

 

16. Fermat's principle of ray optics states, "A ray of light follows the path between two points which requires the least time." This principle can be used to derive which of the following?

 

Ⅰ. Snell's law of refraction

Ⅱ. The law of reflection

Ⅲ. Rayleigh's criterion for resolution

 

 

⑴ answer: D

⑵ Fermat's principle can be used in geometrical optics. 

 

 

17. Consider two identical systems, 1 and 2, each consisting of a planet in circular orbit about a much heavier star. For system 1 the radius of the orbit is a, and for system 2 the radius of the orbit is 4a. Which of the following gives the ratio, T₁ / T₂, of the period of system 1 to the period of system 2?

 

 

⑴ answer: D

⑵ Kepler's 3rd law : T₁² : T₂² = a³ : 64a³ 

 

 

 

18. Two identical satellites, A and B, are in circular orbits around Earth. The orbital radius of A is twice that of B. Which of the following gives the ratio of the angular momentum of A to the angular momentum of B?

 

 

⑴ answer: C

⑵ angular momentum formula

 

 

 

19. A 10 kg box slides horizontally without friction at a speed of 1 m/s. At one point, a constant force is applied to the box in the direction of its motion. The box travels 5 m with the constant force applied. The force is then removed, leaving the box with a speed of 2 m/s. Which of the following gives the magnitude of the applied force?

 

 

⑴ answer: C

⑵ F × 5 = 0.5 × 10 × (2² - 1²) = 15 ⇔ F = 3 (N)

 

 

20. What is the magnitude of the magnetic field at the center of a circular conducting loop of radius a that is carrying current I? 

 

 

⑴ answer: D

⑵ based on Biot-Savart law 

 

입력: 2022.12.26 22:37