Engineering Physics Multiple Choice Questions on “Mechanism of Light Emission”.
1. In X-ray emission tubes, X-ray is emitted by the acceleration of _____
a) Atoms
b) Protons
c) Electrons
d) Neutrons
Answer: c
Clarification: In X-ray emission tubes, the electrons are accelerated by a very high voltage and then decelerated very fast by introducing a metal plate. In this process, the Kinetic energy of electrons is converted into light energy and, thus, X-ray is emitted.
2. Hot bodies emit a specific type of radiation. What are they called?
a) X-rays
b) Black-body radiation
c) Gamma radiations
d) Visible light
Answer: b
Clarification: The phenomenon of black—body radiations was given by Max Planck. He stated that hot bodies emit radiation over a wide range of wavelengths. An ideal body is the one that emits and absorbs radiation of all frequencies. Such a body called a Black Body and the radiations are called Black body radiations.
3. An iron rod is heated. As it gets heated, it changes color. Which of the following colors indicates a very high temperature?
a) Red
b) Orange
c) White
d) Blue
Answer: d
Clarification: As the body gets hotter, the frequency of the emitted radiation keeps on increasing. Blue color has the highest frequency out of red, orange and white. Thus, as the iron rod gets heated first it would become red, then orange, then white and then finally blue.
4. Which of the following may not be conserved in a photon-particle collision?
a) Total Energy
b) Total momentum
c) Number of photons
d) Number of particles
Answer: c
Clarification: In a photon-particle collision, total energy and the total momentum are conserved. However, the number of photons may vary. Some photons may get absorbed or new photons may be created. Thus, the number of photons may not be conserved in a collision.
5. When an electron jumps from an excited state to ground state it __________
a) Emits a photon having energy 13.6 eV
b) Absorbs a photon having energy 13.6 eV
c) Emits a photon having energy the same as the energy difference between the two states
d) Absorbs a photon having energy the same as the energy difference between the two states
Answer: c
Clarification: Electron in the ground state is extremely stable. Hence, when an electron is in an excited state it tends to come back to its ground state. In this process, a photon is emitted. The Emitted photon has energy equal to the energy difference between the two energy states.
6. Stimulated emission is used for the production of ____________
a) Laser
b) X-rays
c) Gamma rays
d) Infrared rays
Answer: a
Clarification: Stimulated emission is the process in which matter at high energy state is perturbed by a photon having energy equal to the energy difference between the current excited state and a lower state. The matter jumps back to the lower state releasing another photon of the same energy. This process is used for the generation of LASERS.
7. Radioactive decay of the nucleus emits ____________
a) Ultraviolet rays
b) X-Rays
c) Infra-red
d) Gamma rays
