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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

what is principle of superposition
Jyoti Reply
what are questions that are likely to come out during exam
King Reply
what is electricity
Jyoti Reply
watt is electricity.
Adam
electricity ka full definition with formula
Jyoti
If a point charge is released from rest in a uniform electric field will it follow a field line? Will it do so if the electric field is not uniform?
Sadaqat Reply
Maxwell's stress tensor is
Ami Reply
Yes
doris
neither vector nor scalar
Anil
if 6.0×10^13 electrons are placed on a metal sphere of charge 9.0micro Coulombs, what is the net charge on the sphere
Rita Reply
18.51micro Coulombs
ASHOK
Is it possible to find the magnetic field of a circular loop at the centre by using ampere's law?
Rb Reply
Is it possible to find the magnetic field of a circular loop at it's centre?
Rb Reply
yes
Brother
The density of a gas of relative molecular mass 28 at a certain temperature is 0.90 K kgmcube.The root mean square speed of the gas molecules at that temperature is 602ms.Assuming that the rate of diffusion of a gas in inversely proportional to the square root of its density,calculate the density of
Gifty Reply
A hot liquid at 80degree Celsius is added to 600g of the same liquid originally at 10 degree Celsius. when the mixture reaches 30 degree Celsius, what will be the total mass of the liquid?
Gifty
Under which topic
doris
what is electrostatics
Yakub Reply
Study of charges which are at rest
himanshu
Explain Kinematics
Glory Reply
Two equal positive charges are repelling each other. The force on the charge on the left is 3.0 Newtons. Using your notes on Coulomb's law, and the forces acting on each of the charges, what is the force on the charge on the right?
Nya Reply
Using the same two positive charges, the left positive charge is increased so that its charge is 4 times LARGER than the charge on the right. Using your notes on Coulomb's law and changes to the charge, once the charge is increased, what is the new force of repulsion between the two positive charges?
Nya
A mass 'm' is attached to a spring oscillates every 5 second. If the mass is increased by a 5 kg, the period increases by 3 second. Find its initial mass 'm'
Md Reply
a hot water tank containing 50,000g of water is heated by an electric immersion heater rated at 3kilowatt,240volt, calculate the current
Samuel Reply
what is charge
Aamir Reply
product of current and time
Jaffar
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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