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Two lightbulbs have cylindrical filaments much greater in length than in diameter. The evacuated bulbs are identical except that one operates at a filament temperature of 2 100°C and the other operates at 2 000°C. (a) Find the ratio of the power emitted by the hotter lightbulb to that emitted by the cooler lightbulb. (b) With the bulbs operating at the same respective temperatures, the cooler lightbulb is to be altered by making its filament thicker so that it emits the same power as the hotter one. By what factor should the radius of this filament be increased?
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Chapter 19 Solutions
Bundle: Physics for Scientists and Engineers with Modern Physics, Loose-leaf Version, 10th + WebAssign Printed Access Card for Serway/Jewett's Physics for Scientists and Engineers, 10th, Multi-Term
- A cylindrical resistor element on a circuit board dissipates 0.15 W of power in an environment at 40°C. The resistor is 1.2 cm long, and has a diameter of 0.3 cm. Assuming heat to be transferred uniformly from all surfaces, determine the amount of heat this resistor dissipates during a 24 h period;arrow_forward(a) How much energy is necessary to heat 7.0 kg of water from room temperature (20°C) to its boiling point? (Assume no energy loss.)(b) If electrical energy were used, how much would this cost at 19¢ per kWh?arrow_forwardAn infrared heater for a sauna has a surface area of 0.050 m2 and an emissivity of 0.84. What temperature must it run at if the required power is 360 W? Neglect the temperature of the environment.arrow_forward
- Diameter of a Solid conductor wire is 2.54 cm and the thickness of the insulation is 3 mm. When the current is flowing, the rate of heat dissipation from the wire is 417 W per unit length of wire. If the outer surface temperature of the insulation is 28 °C, Calculate the inner surface temperature of the insulation. Take the thermal conductivity of the insulation material as 0.44 W/m K.arrow_forwardA bulb delivers 25 W of radiant energy when its filament is at 1500 °C . If the temperature increases by 300 °C , what is the new rate of energy radiated by this bulb?arrow_forwardA long length of copper wire is initially at room temperature (23∘C) when it is connected across the terminals of an ideal potential source of V0=10V. The power dissipated by the wire as heat is initially measured to be Pinitial = 50W. The wire begins to heat up, but eventually reaches a "steady state" temperature (i.e., the wire is now warmer than the original room temperature, but it is no longer getting any hotter.) At this point, the power dissipated by the same circuit is Pfinal = 44.3 W. Calculate the final temperature of the copper wire. (You can find the temperature coefficient of resistivity for copper from the table in the text above.)arrow_forward
- What is the role of “loose” electrons in heat conductors? (A) Loose electrons move quickly away from hot locations, making it impossible for energy to move and making the object a good insulator. (B) Loose electrons absorb energy, giving materials a high specific heat capacity. (C) Loose electrons vibrate and emit radiation that carries energy through the material at the speed of light. (D) Loose electrons transfer energy rapidly through a solid.arrow_forwardIn the comparison of heat and electrical energy flowing along a well insulated conductor which of these is/are true? 1) The Pd across the ends of the conductor is analogous to the temperature difference 44. between the ends of the conductor. 2) The electric current is analogous to the rate of flow of heat 3) The electrical resistance is analogous to the of thermal conductivityarrow_forwardA fluorescent tube has a power rating of 52 W. It is also left on for 3 hours, and 92 170 J of energy was used to produce radiant energy. What is the efficiency of the fluorescent tube?arrow_forward
- Physics for Scientists and Engineers: Foundations...PhysicsISBN:9781133939146Author:Katz, Debora M.Publisher:Cengage LearningPrinciples of Physics: A Calculus-Based TextPhysicsISBN:9781133104261Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningPhysics for Scientists and Engineers, Technology ...PhysicsISBN:9781305116399Author:Raymond A. Serway, John W. JewettPublisher:Cengage Learning
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