An incandescent lightbulb is an inexpensive but highly inefficient device that converts electrical energy into light. It converts about 10 percent of the electrical energy it consumes into light while converting the remaining 90 percent into heat. (A fluorescent lightbulb will give the same amount of light while consuming only one-fourth of the electrical energy, and it will last 10 times longer than an incandescent lightbulb.) The glass bulb of the lamp heats up very quickly as a result of absorbing all that heat and dissipating it to the surroundings by convection and radiation. Consider a 10-cm-diameter 100-W lightbulb cooled by a fan that blows air at 30°C to the bulb at a velocity of 2 m/s. The surrounding surfaces are also at 30°C, and the emissivity of the glass is 0.9. Assuming 10 percent of the energy passes through the glass bulb as light with negligible absorption and the rest of the energy is absorbed and dissipated by the bulb itself, determine the equilibrium temperature of the glass bulb. Assume a surface temperature of 100°C for evaluation of ms. Is this a good assumption?
Energy transfer
The flow of energy from one region to another region is referred to as energy transfer. Since energy is quantitative; it must be transferred to a body or a material to work or to heat the system.
Molar Specific Heat
Heat capacity is the amount of heat energy absorbed or released by a chemical substance per the change in temperature of that substance. The change in heat is also called enthalpy. The SI unit of heat capacity is Joules per Kelvin, which is (J K-1)
Thermal Properties of Matter
Thermal energy is described as one of the form of heat energy which flows from one body of higher temperature to the other with the lower temperature when these two bodies are placed in contact to each other. Heat is described as the form of energy which is transferred between the two systems or in between the systems and their surrounding by the virtue of difference in temperature. Calorimetry is that branch of science which helps in measuring the changes which are taking place in the heat energy of a given body.
An incandescent lightbulb is an inexpensive but
highly inefficient device that converts electrical energy into
light. It converts about 10 percent of the electrical energy it
consumes into light while converting the remaining 90 percent
into heat. (A fluorescent lightbulb will give the same
amount of light while consuming only one-fourth of the
electrical energy, and it will last 10 times longer than an
incandescent lightbulb.) The glass bulb of the lamp heats up
very quickly as a result of absorbing all that heat and dissipating
it to the surroundings by
Consider a 10-cm-diameter 100-W lightbulb cooled by a
fan that blows air at 30°C to the bulb at a velocity of 2 m/s.
The surrounding surfaces are also at 30°C, and the emissivity
of the glass is 0.9. Assuming 10 percent of the energy passes
through the glass bulb as light with negligible absorption and
the rest of the energy is absorbed and dissipated by the bulb
itself, determine the equilibrium temperature of the glass
bulb. Assume a surface temperature of 100°C for evaluation
of ms. Is this a good assumption?
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