MCQs of blackbody & its radiation

1. Questions & answers of blackbody & its radiation BY JAYAM CHEMISTRY ADDA

2. 01. What is a blackbody? Explanation: A. A celestial object A hollow solidified enclosure having an opaque surface with a pinhole is an assumption of a perfect blackbody by the physicist Gustav Kirchhoff. B. A chemical substance 01. C. A rigid solid enclosure Answer: A rigid solid enclosure Jayam chemistry adda

3. 02. Which of the following is not an example of a partial blackbody? Explanation: Heating filament of a toaster A. A perfect blackbody is unreal. All earthly objects with absorbing abilities greater than 0.95 are imperfect blackbodies called grey bodies. Thin gold foil absorbing ability is much less than the said value. Hence, it is not an example of a partial blackbody. B. Thin gold foil 02. C. Platinum black Answer: Thin gold foil Jayam chemistry adda

4. 03. A blackbody emits_________ Explanation: Heat-assimilated electromagnetic radiations A. The thermal electromagnetic radiation emitted from a blackbody is known as blackbody radiation. A blackbody emits the absorbed electromagnetic light only on heating. Hence, it is a heat-combined electromagnetic radiation. B. Thermal radiations 03. C. Light radiations Answer: Heat-assimilated electromagnetic radiations Jayam chemistry adda

5. 04. Which of the following substance has the highest absorbing power? Explanation: A. Polished Silver Lamp black is a partial blackbody with 0.98 absorbing power. It implies lamp black can intake 98% of the incident that falls on its surface. The diamond and polished silver are not partial blackbodies whose absorbing capacities lie below 0.95. B. Diamond 04. C. Lamp black Answer: Lamp black Jayam chemistry adda

6. 05. What is the emissivity of a pure copper filament? Explanation: Less than one A. When an object and a perfect blackbody are at a fixed temperature state, their radiant emittances ratio is called emissivity. Anyhow the emissivity of an ideal blackbody is always one. But all other earthly materials' emissivity lies below one. B. Greater than one 05. C. Equal to one Answer: Less than one Jayam chemistry adda

7. 06. Which of the following is an application of blackbody radiation? Explanation: A. Cellular communications A burglar alarm is a security device with a loud alarm to alert about the opening of doors and windows. It consists of blackbody radiation detectors and sensors that connect with the control panel systems. B. Satellite communications 06. C. Burglar alarm Answer: Burglar alarm Jayam chemistry adda

8. 07. Blackbody radiations comprise _____________ Explanation: A. Protons Following Planck's law, blackbody radiation comprises discrete radiant energy particles called photons. B. Photons 07. C. Positrons Answer: Photons Jayam chemistry adda

9. 08. The following are examples of hot bodies identical in every respect in thermal equilibrium conditions. Which one among them cools last? Explanation: A. A solid cube The rate of thermal emissions of a blackbody varies directly with its surface area. Objects with a large surface area have high emissive power. The solid sphere has a low surface area than the other hot bodies. Hence, it cools last. A solid sphere B. 08. C. A solid cone Answer: A solid sphere Jayam chemistry adda

10. 09. What is the color of blackbody radiation? Explanation: A. Red The color of blackbody radiation depends only on the enclosure's temperature. The blackbody radiation exhibit colors when its wavelength lies between 350-750 nm, and the enclosure's temperature ranges between 3800-8300 Kelvin approximately. Initially, at 3800 K, the radiation appears in dull red. At higher temperatures, the radiation color follows the reverse VIBGYOR pattern. Finally, the radiation becomes violet- colored at 8257 Kelvin. At above 12000 K, the radiation becomes white. Then it enters the ultraviolet region part of the spectrum with further temperature rise. B. Blue 09. It depends upon the enclosure's temperature C. Answer: It depends upon the enclosure's temperature Jayam chemistry adda

11. 10. Which of the following surfaces are good reflectors of blackbody radiations? Explanation: Black coarse surfaces A. Polished surfaces are even that makes them better reflectors of light. They reflect light parallel to the incident light ray. B. Polished surfaces 10. C. Rough surfaces Answer: Polished surfaces Jayam chemistry adda

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13. 11. Intensity of blackbody radiation is maximum at____________ Explanation: Longer radiation wavelengths A. The blackbody curve depicts that energy distribution is not uniform over broad wavelength ranges. As a result, the blackbody radiation intensity rises with emissive power at shorter wavelengths. It continues until it reaches the peak wavelength position λmax. For a fixed temperature T, the radiation intensity is maximum at λmax. B. Shorter radiation wavelengths 11. λmax C. Answer: λmax Jayam chemistry adda

14. 12. The blackbody curve is the variation of ______ and ______ Explanation: Emissive power and temperature A. A blackbody curve is a graph between blackbody radiations' emissive power and their wavelength at fixed temperature conditions. The blackbody radiation graph is a hill-shaped curve depicting non-uniform spectral energy densities of blackbody radiation emissions. Moreover, the crest position of the blackbody curve shifts towards shorter wavelengths at higher temperatures by Wien's displacement law. B. Emissive power and wavelength 12. C. Temperature and wavelength Answer: Emissive power and wavelength Jayam chemistry adda

15. 13. Blackbody spectrum is a _______________spectrum Explanation: Continuous radiation emission A. The blackbody spectrum is a patterned arrangement of blackbody radiation emissions in the increasing order of frequencies or in the decreasing order of their wavelengths. Besides, it is a continuous emission spectrum due to the absence of distinct boundary separation between the spectral bands. In the blackbody spectrum, one spectral band merges into the other without partition. Like the electromagnetic spectrum, it is a never-ending blackbody radiation emission spectrum. B. Discontinuous radiation absorption 13. Line spectra of emitted blackbody radiations C. Answer: Continuous radiation emission spectrum Jayam chemistry adda

16. 14. By Lambert's law, the distribution of blackbody radiation in various directions is __________ Explanation: A. Identical Blackbody radiation emissions are homogeneous in all directions. Hence, they are isotropic. B. Irregular 14. C. Intermittent Answer: Identical Jayam chemistry adda

17. 15. The blackbody emissions obey __________law Explanation: Quantum law A. Planck's quantum law was the first theory that invented the particle character of energy. And it successfully explained the energy distributions of blackbody curves for shorter and longer radiation wavelengths, unlike Rayleigh-Jeans law and Wien displacement law. It elucidated the interaction of electromagnetic radiations with the matter. Further, it calculated the magnitude of blackbody emission energies from the radiation frequencies. B. Energy conservation law 15. C. Biot-savart law Answer: Quantum law Jayam chemistry adda

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