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Question # 1: Conceptual (a) What is a blackbody? Does a blackbody actually exist? (h) What is on alaotromagnoti wovo? How does it differ from a sound wovo?

Question # 1: Conceptual (a) What is a blackbody? Does a blackbody actually exist? (h) What is on alaotromagnoti wovo? How does it differ from a sound wovo?

Elements Of Electromagnetics
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
Section: Chapter Questions
Problem 1.1MA
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Question # 1: Conceptual (a) What is a blackbody? Does a blackbody actually exist? (b) What is an electromagnetic wave? How does it differ from a sound wave? (c) Electricity is generated and transmitted in power lines at a frequency of 60 Hz (1 Hz = 1 cycle per second). Determine the wavelength of the electromagnetic waves generated by the passage of electricity in power lines. (d) Define the properties emissivity and absorptivity. When are these two properties equal to each other? (e) Define the properties reflectivity and transmissivity and discuss the different forms of reflection. (f) What is a graybody? How does it differ from a blackbody? What is a diffuse gray surface? Question # 2: Short Problems (a) A cordless telephone is designed to operate at a frequency of 8.5 x 108 Hz. Determine the wavelength of these telephone waves. (b) A microwave oven is designed to operate at a frequency of 2.8×10° Hz. Determine the wavelength of these microwaves and the energy of each microwave. (c) Consider a 20-cm × 20-cm × 20-cm cubical body at 1000 K suspended in the air. Assuming the body closely approximates a blackbody, determine (a) the rate at which the cube emits radiation energy, in W, and (b) the spectral blackbody emissive power at a wavelength of 4 µm. (d) The temperature of the filament of an incandescent lightbulb is 3200 K. Treating the filament as a blackbody, determine the fraction of the radiant energy emitted by the filament that falls in the visible range. Also, determine the wavelength at which the emission of radiation from the filament peaks. Question # 3: A surface has an absorptivity of as= 0.85 for solar radiation and an emissivity of ε = 0.5 at room temperature. The surface temperature is observed to be 350 K when the direct and the diffuse components of solar radiation are GD = 350 and Ga = 400 W/m², respectively, and the direct radiation makes a 30° angle with the normal of the surface. Taking the effective sky temperature to be 280 K, determine the net rate of radiation heat transfer to the surface at that time. Question # 4: A 3-mm-thick glass window transmits 90 percent of the radiation between λ = 0.3 and 3.0 μm and is essentially opaque for radiation at other wavelengths. Determine the rate of radiation transmitted through a 2-m × 2-m glass window from blackbody sources at (a) 5800 K and (b) 1000 K.
Transcribed Image Text:Question # 1: Conceptual (a) What is a blackbody? Does a blackbody actually exist? (b) What is an electromagnetic wave? How does it differ from a sound wave? (c) Electricity is generated and transmitted in power lines at a frequency of 60 Hz (1 Hz = 1 cycle per second). Determine the wavelength of the electromagnetic waves generated by the passage of electricity in power lines. (d) Define the properties emissivity and absorptivity. When are these two properties equal to each other? (e) Define the properties reflectivity and transmissivity and discuss the different forms of reflection. (f) What is a graybody? How does it differ from a blackbody? What is a diffuse gray surface? Question # 2: Short Problems (a) A cordless telephone is designed to operate at a frequency of 8.5 x 108 Hz. Determine the wavelength of these telephone waves. (b) A microwave oven is designed to operate at a frequency of 2.8×10° Hz. Determine the wavelength of these microwaves and the energy of each microwave. (c) Consider a 20-cm × 20-cm × 20-cm cubical body at 1000 K suspended in the air. Assuming the body closely approximates a blackbody, determine (a) the rate at which the cube emits radiation energy, in W, and (b) the spectral blackbody emissive power at a wavelength of 4 µm. (d) The temperature of the filament of an incandescent lightbulb is 3200 K. Treating the filament as a blackbody, determine the fraction of the radiant energy emitted by the filament that falls in the visible range. Also, determine the wavelength at which the emission of radiation from the filament peaks. Question # 3: A surface has an absorptivity of as= 0.85 for solar radiation and an emissivity of ε = 0.5 at room temperature. The surface temperature is observed to be 350 K when the direct and the diffuse components of solar radiation are GD = 350 and Ga = 400 W/m², respectively, and the direct radiation makes a 30° angle with the normal of the surface. Taking the effective sky temperature to be 280 K, determine the net rate of radiation heat transfer to the surface at that time. Question # 4: A 3-mm-thick glass window transmits 90 percent of the radiation between λ = 0.3 and 3.0 μm and is essentially opaque for radiation at other wavelengths. Determine the rate of radiation transmitted through a 2-m × 2-m glass window from blackbody sources at (a) 5800 K and (b) 1000 K.
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