What, roughly, is the percentage of the mass-energy of the universe that is thought to consist of dark matter?
A. 27%
B. 68%
C. 80%
D. 5%
The correct answer is: A
Rationale: Dark matter makes up about 27% of the universe's mass-energy, while dark energy constitutes about 68%, and normal matter makes up about 5%.
In a thought experiment, an observer is enclosed in a windowless elevator that is in freefall. According to the equivalence principle, how would the observer perceive their own state of motion?
A. Moving upwards at an increasing speed.
B. As being at rest or moving with a constant velocity.
C. Accelerating downwards.
D. Moving downwards at a constant speed.
The correct answer is: B
Rationale: The equivalence principle states that the effects of gravity are indistinguishable from those of acceleration. In freefall, the observer and the elevator are accelerating at the same rate, creating the sensation of weightlessness and making it impossible to distinguish between being at rest or in constant motion.
What is the physical principle that prevents perpetual motion machines from being possible?
A. The second law of thermodynamics
B. The first law of thermodynamics
C. The third law of thermodynamics
D. The law of conservation of energy
The correct answer is: A
Rationale: The second law of thermodynamics, which states that the entropy of an isolated system always increases over time, prohibits perpetual motion machines. It implies that energy tends to disperse and become less useful, making it impossible to create a system that continuously produces energy without any input.
When light passes from a medium with a higher refractive index to a medium with a lower refractive index, what optical phenomenon can occur if the angle of incidence exceeds a certain critical angle?
A. Diffraction
B. Refraction
C. Total internal reflection
D. Dispersion
The correct answer is: C
Rationale: When light travels from a denser medium to a rarer medium at an angle greater than the critical angle, it undergoes total internal reflection, where all the light is reflected back into the denser medium.
Which fundamental force is responsible for the radioactive decay of atomic nuclei?
A. Strong nuclear force
B. Weak nuclear force
C. Electromagnetic force
D. Gravitational force
The correct answer is: B
Rationale: The weak nuclear force governs radioactive decay processes, such as beta decay, where a neutron in the nucleus transforms into a proton, an electron, and an antineutrino.
What is the name given to the hypothetical particle that mediates the gravitational force?
A. Higgs boson
B. Gluon
C. Graviton
D. Photon
The correct answer is: C
Rationale: The graviton is a hypothetical elementary particle that is thought to mediate the gravitational force, similar to how photons mediate the electromagnetic force. However, gravitons have not yet been directly observed.
What is the property of a material that determines its ability to resist the flow of electric current?
A. Resistance
B. Capacitance
C. Inductance
D. Conductance
The correct answer is: A
Rationale: Resistance is the property of a material that quantifies its opposition to the flow of electric current. A higher resistance indicates a lower ability to conduct electricity.
How does the wavelength of light change when it transitions from a vacuum into a medium with a higher refractive index?
A. It increases.
B. It remains the same.
C. It decreases.
D. It becomes zero.
The correct answer is: C
Rationale: When light enters a medium with a higher refractive index, its speed decreases, which in turn causes its wavelength to decrease as well. The frequency of the light remains constant.
What is the name of the phenomenon where two waves superimpose to form a resultant wave with a larger amplitude?
A. Interference
B. Diffraction
C. Polarization
D. Dispersion
The correct answer is: A
Rationale: Interference occurs when two or more waves overlap and combine to form a new wave. Constructive interference happens when the waves are in phase, resulting in a wave with a larger amplitude.
What is the name of the process by which a heavy atomic nucleus splits into two or more lighter nuclei, releasing a large amount of energy?
A. Nuclear fusion
B. Nuclear fission
C. Radioactive decay
D. Nuclear transmutation
The correct answer is: B
Rationale: Nuclear fission is the process where a heavy nucleus, such as uranium, splits into smaller nuclei, releasing a significant amount of energy. This process is the basis for nuclear power plants and atomic bombs.