31 practice MCQs on the photoelectric effect, photons, atomic spectra, lasers, X-rays, relativity and semiconductor electronics. Every question has the correct answer and an explanation.
Start free — 20 questionsModern Physics and Atomic Spectra is part of the MDCAT Physics syllabus. This page collects Modern Physics and Atomic Spectra MCQs in the style of past MDCAT papers — below are 12 of them with answers and explanations, and the full set of 31 questions is in the HighYield MDCAT QBank.
This chapter covers: the photoelectric effect, photons, atomic spectra, lasers, X-rays, relativity and semiconductor electronics.
Correct answer: D. There is a population inversion of photons
Lasers work by achieving a population inversion among excited atoms, which upon stimulated emission produces coherent, monochromatic light.
Correct answer: A. hf Kα = E L – E K
When an electron from the L shell fills a vacancy in the K shell, the emitted photon's energy is given by hfKα = EL − EK, the energy difference between the two shells.
Correct answer: C. Surveying for construction of tunnels
Helium-neon lasers, producing a precise, coherent red beam, are widely used in surveying applications such as alignment for tunnel construction.
Correct answer: C. Computerized Axial Topography
Computerized Axial Tomography (CAT/CT scanning) is a direct practical application of X-rays, producing detailed cross-sectional body images.
Correct answer: C. Holography
Holography is the process of generating three-dimensional images of objects using coherent laser light.
Correct answer: D. 60%
In a helium-neon laser gas mixture, helium typically makes up the larger proportion (around 85%), since it serves to efficiently transfer excitation energy to the neon atoms.
Correct answer: A. 10-6 m
The base region of a transistor is extremely thin, typically on the order of 10⁻⁶ m, to allow efficient charge carrier transfer between emitter and collector.
Correct answer: C. Zero
Photons are massless particles, meaning they have no rest mass. They only have energy and momentum.
Correct answer: C. Greater energy and momentum
The correct statement is C. Greater energy and momentum. In the Compton effect, the incident photon has greater energy and momentum compared to the scattered photon, as energy and momentum are conserved during the scattering process.
Correct answer: C. Voltage and current
B is the correct option. A diode characteristic curve, also known as the I-V (current-voltage) curve, illustrates the relationship between the current flowing through the diode and the voltage across it.This curve helps in understanding the behavior of the diode in different operating conditions, including forward bias (where current flows) and reverse bias (where very little current flows).Thus, the correct answer is that a diode characteristic curve is a plot between Voltage and current.
Correct answer: B. Law of conservation of mass-energy
In the special theory of relativity, Albert Einstein showed that mass (m) and energy (E) are equivalent and can be converted into each other, as expressed by the famous equation:E = mc^2This means that the laws of conservation of energy and conservation of mass are no longer separate, but are combined into a single law: the law of conservation of mass-energy. This law states that the total mass-energy of a closed system remains constant over time.
Correct answer: A. Zero
Photons, being massless particles, have a rest mass of zero. According to special relativity, photons always travel at the speed of light (c) and have no rest mass. This means that a photon's energy (E) is equal to its momentum (p) multiplied by the speed of light (E = pc), and its rest mass is zero.
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