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You can explore a simulation of the greenhouse effect that takes the point of view that the atmosphere scatters (redirects) infrared radiation rather than absorbing it and reradiating it. You may want to run the simulation first with no greenhouse gases in the atmosphere and then look at how adding greenhouse gases affects the infrared radiation from the Earth and the Earth’s temperature.

Problem-solving strategy: effects of heat transfer

  1. Examine the situation to determine what type of heat transfer is involved.
  2. Identify the type(s) of heat transfer—conduction, convection, or radiation.
  3. Identify exactly what needs to be determined in the problem (identify the unknowns). A written list is useful.
  4. Make a list of what is given or what can be inferred from the problem as stated (identify the knowns).
  5. Solve the appropriate equation for the quantity to be determined (the unknown).
  6. For conduction, use the equation P = k A Δ T d . [link] lists thermal conductivities. For convection, determine the amount of matter moved and the equation Q = m c Δ T , along with Q = m L f or Q = m L V if a substance changes phase. For radiation, the equation P net = σ e A ( T 2 4 T 1 4 ) gives the net heat transfer rate.
  7. Substitute the knowns along with their units into the appropriate equation and obtain numerical solutions complete with units.
  8. Check the answer to see if it is reasonable. Does it make sense?

Check Your Understanding How much greater is the rate of heat radiation when a body is at the temperature 40 ° C than when it is at the temperature 20 ° C ?

The radiated heat is proportional to the fourth power of the absolute temperature . Because T 1 = 293 K and T 2 = 313 K , the rate of heat transfer increases by about 30% of the original rate.

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Summary

  • Heat is transferred by three different methods: conduction, convection, and radiation.
  • Heat conduction is the transfer of heat between two objects in direct contact with each other.
  • The rate of heat transfer P (energy per unit time) is proportional to the temperature difference T h T c and the contact area A and inversely proportional to the distance d between the objects.
  • Convection is heat transfer by the macroscopic movement of mass. Convection can be natural or forced, and generally transfers thermal energy faster than conduction. Convection that occurs along with a phase change can transfer energy from cold regions to warm ones.
  • Radiation is heat transfer through the emission or absorption of electromagnetic waves.
  • The rate of radiative heat transfer is proportional to the emissivity e . For a perfect blackbody, e = 1 , whereas a perfectly white, clear, or reflective body has e = 0 , with real objects having values of e between 1 and 0.
  • The rate of heat transfer depends on the surface area and the fourth power of the absolute temperature:
    P = σ e A T 4 ,

    where σ = 5.67 × 10 8 J/s · m 2 · K 4 is the Stefan-Boltzmann constant and e is the emissivity of the body. The net rate of heat transfer from an object by radiation is
    Q net t = σ e A ( T 2 4 T 1 4 ) ,

    where T 1 is the temperature of the object surrounded by an environment with uniform temperature T 2 and e is the emissivity of the object.

Questions & Answers

A proton initially at rest falls through a p.d of 25000V. what speed does it gain?
Minister Reply
what is the reaction of heat on magnet
ORIZINO Reply
what is a physical significant of electric dipole moment .
PRANAB Reply
A dipole moment it's a mechanical electrical effect used in nature
Antonio
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Malik Reply
at what temperature is the degree Fahrenheit equal to degree Celsius
Grace Reply
Celsius and Faharaneith are different, never equal
Antonio
find their liners express of n=a+b/T² ( plot graph n against T)
Donsmart Reply
Radio Stations often advertis "instant news,,if that meens you can hear the news the instant the radio announcer speaks it is the claim true? what approximate time interval is required for a message to travel from Cairo to Aswan by radio waves (500km) (Assume the waves Casbe detected at this range )
mahmod Reply
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thevenin
Oladejo Reply
Can someone please predict the trajectory of a point charge in a uniform electric field????
erlinda Reply
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zahid Reply
so basically the electric lines or the field lines
zach Reply
it's the measure of the flow of an electric field through a certain area
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What is electric flux
Pranju Reply
how to calculate the magnetic force if the B field is depend on the coordinate
Ivan Reply
Practice Key Terms 9

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Source:  OpenStax, University physics volume 2. OpenStax CNX. Oct 06, 2016 Download for free at http://cnx.org/content/col12074/1.3
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