The Solution for GRE Physics Practice Test [81-100]
추천글 : 【GRE】 Solution for GRE Physics Practice Test
81. White light is normally incident on a puddle of water (index of refraction 1.33). A thin (500 nm) layer of oil (index of refraction 1.5) floats on the surface of the puddle. Of the following, the most strongly reflected wavelength is
⑴ answer: C
⑶ wave 1. fixed end refraction : air → water → air. phase conversion by 180°
⑷ wave 2. free end refraction : air → oil → water → oil → air. no phase conversion
⑸ constructive interference condition
82. As represented in the figure below, a light ray refracts from air into a rectangular block of plastic with an index of refraction n > 1. At a point on the side of the block, the ray partly reflects (at an angle of 60°) and partly refracts. The value of the angle α is
⑴ answer: D
⑵ the law of reflection : θ = 30°
⑶ partly reflection = critical point : n sin 60 ° = 1 ⇔ n = 2 / √3
⑷ Snell's law : n sin θ = 1 / √3 = sin α
83. Assume that the solar flux at Earth's surface is 1,000 W/m2 and that the sunlight is normal to a completely reflecting surface with an area of 3 m2. What is the total radiation force exerted on the surface?
⑴ answer: C
⑵ special theory of relativity
84. The hydrogen lines observed in the spectrum of the quasar 3C9 are shifted so far into the red that their wavelengths are three times as long as those observed in the light from hydrogen atoms at rest in a laboratory on Earth. If it is assumed that the shift is entirely due to the relative motion of 3C9 and Earth, the relative speed of the quasar is
⑴ answer: C
⑵ redshift due to the cosmological Doppler effect (ref 1, ref 2)
85. Protons used in cancer therapy are typically accelerated to about 0.6c. How much work must be done on a particle of mass m in order for it to reach this speed, assuming it starts at rest?
⑴ answer: A
⑵ kinetic energy for the theory of relativity
86. The sign of the charge carriers in a doped semiconductor can be deduced by measuring which of the following properties?
⑴ answer: E
87. In the experimental setup below, two masses, m1 and m2, are connected by a massless string over a massless pulley. Mass m1 slides on a frictionless surface. The values of the two masses can be measured, as well as the distance d and the speed of mass m1 as it passes x1 and again at x2. The experiment can be used to do which of the following?
⑴ answer: E
⑵ Ⅰ. External force is applied so that momentum conservation cannot be established.
⑶ Ⅱ. The law of conservation of mechanical energy can be established.
⑷ Ⅲ. When Ⅱ corresponds to an integral analysis, Ⅲ corresponds to a differential analysis.
88. An airplane drops a payload while traveling due north, parallel to the ground, at a constant speed of 100 m/s. If air resistance is neglected, what is the velocity of the payload relative to the plane 4.0 s after it is released?
⑴ answer: B
⑵ horizontal : The airplane and payload are the same 100 m/s.
⑶ vertical : Only payload has a vertical velocity, which is 10 m/s2 × 4.0 s = 40 m/s.
89. Two balls, identical in every way except that one has twice the mass of the other, are dropped from rest from the same height so that they both reach terminal speed before hitting the ground. If it is assumed that the drag force varies like the speed squared, what is the ratio of the terminal speeds of the balls? (Note: The subscripts h and ℓ denote the heavy and light masses, respectively.)
⑴ answer: B
90. One end of a horizontal, massless spring is attached to a wall. A mass of 0.30 kg is attached to the other end of the spring and rests on a table. The mass is displaced 0.030 m from its equilibrium position and released. It has a speed of 0.040 m/s as it passes through its equilibrium position. In the absence of friction, what is the total mechanical energy of the system?
⑴ answer: A
91. The diagram below shows a Carnot cycle for an ideal air conditioner, which is to cool a house on a hot summer day. The air conditioner absorbs heat at the lower temperature inside and pumps it to the environment at the higher temperature outside. Which of the following gives the ratio of the heat Qbc absorbed in the house (i.e., between points b and c on the cycle) to the work done during the cycle?
⑴ answer: E
92. A particle in an infinite square well with walls at x = 0 and x = L has energy
The probability that the particle is between x = 0 and x = L/6 is
⑴ answer: B
⑵ the probability density function for particle in a box
⑶ energy formula : n is found to be 3.
⑷ By symmetry, the probability that the particle is between x = 0 and x = L/6 is one-sixth of the total probability, which is 1.
93. An inertial reference frame S' moves at constant speed with respect to a second inertial reference frame S. An observer in S measures the energy E, momentum p, and position x of a moving particle at time t for a particular event. An observer in S' measures energy E' , momentum p' , and position x' at time t' for the same moving particle at the same event. Which of the following is an expression of a relativistic invariant for this event?
⑴ answer: E
⑶ x', t'
⑷ p' = γp
⑸ E' = γE
⑹ E2 = p2c2 + (m0c2)2
94. Consider three identical, ideal capacitors. The first capacitor is charged to a voltage V0 and then disconnected from the battery. The other two capacitors, initially uncharged and connected in series, are then connected across the first capacitor. What is the final voltage on the first capacitor?
⑴ answer: D
⑵ Each identical, ideal capacitor has a capacitance of C.
⑶ The other two capacitors in series can be indicated as C/2.
⑷ Capacitor terminal characteristic
95. A charge of -5.0 µC is distributed uniformly around a ring 1.0 m in radius. A point charge of +3.0 µC is at the center of the ring. The work required to move the point charge 1.0 m in a direction normal to the plane of the ring is most nearly
⑴ answer: A
⑵ Coulomb potential
⑶ calculation
96. The magnetic field inside a long coil of wire (solenoid) has a certain magnitude and direction when the coil is air filled. If a diamagnetic material is inserted in the coil, how do the magnitude and direction of the magnetic field change?
⑴ answer: C
⑵ An diamagnetic object generates a weak magnetic field in the opposite direction to the external magnetic field.
97. The figure below shows two identical simple pendulums, each with mass m and suspended by a massless rod of length a. The pendulums are coupled by a massless spring of force constant k. The coordinates θi measure the angular displacements from vertical, as shown. Which of the following gives the Lagrangian for the system? (Assume small angular displacements θi.)
⑴ answer: A
⑵ Lagrangian analysis : An analysis through the scalar amount such as energy.
⑶ kinetic energy
⑷ gravitational potential energy
⑸ elastic potential energy
⑹ I'm not sure the signs.
98. The spacing between the parallel Bragg planes in a certain crystal is d. Electrons of fixed energy, corresponding to a given wavelength λ, are incident on the crystal. Which of the following is the minimal condition for strong reflection for at least two different angles?
⑴ answer: D
99. Consider an electron in the n = 4, ℓ = 1 state in hydrogen. Which of the following final states can NOT be reached by an allowed transition?
⑴ answer: B
⑵ selection rule : the change in the number quantum of angular momentum, Δℓ, should be ±1.
100. A room-temperature Mössbauer absorption spectrum for the 14.4 keV gamma-ray transition of 57Fe is illustrated in the figure below. From the data, it can be deduced that the lifetime of the 3/2- excited state is approximately
⑴ answer: C
입력: 2023.01.01 02:06
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