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- Heat and heat transfer methods
- Radiation
Summary
- Radiation is the rate of heat transfer through the emission or absorption of electromagnetic waves.
- The rate of heat transfer depends on the surface area and the fourth power of the absolute temperature:
where
is the Stefan-Boltzmann constant and
is the emissivity of the body. For a black body,
whereas a shiny white or perfect reflector has
, with real objects having values of
between 1 and 0. The net rate of heat transfer by radiation is
where
is the temperature of an object surrounded by an environment with uniform temperature
and
is the emissivity of the
object .
Conceptual questions
Satellites designed to observe the radiation from cold (3 K) dark space have sensors that are shaded from the Sun, Earth, and Moon and that are cooled to very low temperatures. Why must the sensors be at low temperature?
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Why are thermometers that are used in weather stations shielded from the sunshine? What does a thermometer measure if it is shielded from the sunshine and also if it is not?
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Problems&Exercises
At what net rate does heat radiate from a
black roof on a night when the roof’s temperature is
and the surrounding temperature is
? The emissivity of the roof is 0.900.
Note that the negative answer implies heat loss to the surroundings.
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(a) Cherry-red embers in a fireplace are at
and have an exposed area of
and an emissivity of 0.980. The surrounding room has a temperature of
. If 50% of the radiant energy enters the room, what is the net rate of radiant heat transfer in kilowatts? (b) Does your answer support the contention that most of the heat transfer into a room by a fireplace comes from infrared radiation?
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Radiation makes it impossible to stand close to a hot lava flow. Calculate the rate of heat transfer by radiation from
of
fresh lava into
surroundings, assuming lava’s emissivity is 1.00.
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(a) Calculate the rate of heat transfer by radiation from a car radiator at
into a
environment, if the radiator has an emissivity of 0.750 and a
surface area. (b) Is this a significant fraction of the heat transfer by an automobile engine? To answer this, assume a horsepower of
and the efficiency of automobile engines as 25%.
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Find the net rate of heat transfer by radiation from a skier standing in the shade, given the following. She is completely clothed in white (head to foot, including a ski mask), the clothes have an emissivity of 0.200 and a surface temperature of
, the surroundings are at
, and her surface area is
.
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Suppose you walk into a sauna that has an ambient temperature of
. (a) Calculate the rate of heat transfer to you by radiation given your skin temperature is
, the emissivity of skin is 0.98, and the surface area of your body is
. (b) If all other forms of heat transfer are balanced (the net heat transfer is zero), at what rate will your body temperature increase if your mass is 75.0 kg?
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Questions & Answers
evolutionary history and relationship of an organism or group of organisms
AI-Robot
the study of living organisms and their interactions with one another and their environments
AI-Robot
HOW CAN MAN ORGAN FUNCTION
the diagram of the digestive system
allimentary cannel
Ogenrwot
They formed in two ways first when one sperm and one egg are splited by mitosis or two sperm and two eggs join together
Oluwatobi
Genetics is the study of heredity
Misack
how does twins formed?
Misack
discuss biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles
the study of living organisms and their interactions with one another and their environment.
Wine
discuss the biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles in an essay form
list any five characteristics of the blood cells
Shaker
lack electricity and its more savely than electronic microscope because its naturally by using of light
advantage of electronic microscope is easily and clearly while disadvantage is dangerous because its electronic. advantage of light microscope is savely and naturally by sun while disadvantage is not easily,means its not sharp and not clear
Abdullahi
cell theory state that every organisms composed of one or more cell,cell is the basic unit of life
Abdullahi
is like gone fail us
DENG
cells is the basic structure and functions of all living things
Ramadan
is organisms that are similar into groups called tara
Yamosa
in what situation (s) would be the use of a scanning electron microscope be ideal and why?
A scanning electron microscope (SEM) is ideal for situations requiring high-resolution imaging of surfaces. It is commonly used in materials science, biology, and geology to examine the topography and composition of samples at a nanoscale level. SEM is particularly useful for studying fine details,
Hilary
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Source:
OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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