1 2 3 4 5 exercises EXERCISES 67 EXERCISES 1. Derive the form of eqn (2.5) using

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1 2 3 4 5 exercises

EXERCISES 67 EXERCISES 1. Derive the form of eqn (2.5) using dimensional analysis. Estimate the characteristic timescale for heat to conduct through a heat shield of thickness 1 cm (p= 5 × 103 kg m 2.2 Explain qualitatively what the 'greenhouse effect' is. Why is it enhanced when the con- centration of CO2 in the atmosphere is increased, and what is the role of water vapour? What are the main concerns about the Earth's climate that arise from increased atmos- pheric GHG concentrations? 2.3 Re-do the calculation in Example 2.3 for a tube with a diameter of 10 mm, with the rest of the data unchanged. 2.4 In a solar cooker, 400 W of sunlight is focused on the underside of a hotplate of area 0.04 m2. The receiving surface of the hotplate has an emissivity of 0.95 for radiation with a wavelength less than 2 m and 0.05 for wavelengths greater than 2 m, when the hotplate has a temperature of 200 °C, estimate the net radiative input and compare with that obtained with a surface with a constant emissivity of 0.95. 5 Consider the following simple model to describe solar radiation incident on the Earth, in which the atmosphere is included. A fraction f of the incident solar flux is absorbed y the atmosphere and a fraction A is reflected, the rest being absorbed by the Earth. Assume that the only heat transfer to the atmosphere from the Earth is by radiation and that,f= 0.25 and A 0.3. Find the temperature TE of the surface of the Earth for radia tive equilibrium 2.6 Balancing the weight pgöz of an element of the atmosphere of unit area and thickness oz with the force arising from the pressure difference-op across it, gives the pressure nation in an atmosphere as dp/dz=-pg. Noting that d(pv-vdp+pd V, = M/K Cp Cv +R, and dU= C dT (for an idealgas), show that the variation of temperature riüht r in an tmhere where the conduction of heat is negligible (adiabatic) is K for

Explanation / Answer

Greenhouse effect is a process by which the earth's atmosphere itself makes the surface of the earth very hot ie it rises the temperature of the earth's surface to an amount which it is not supposed to be in. The temperature change is above that of the temperature that would without the atmosphere. The troposphere which is the lowest layer of the earth's atmosphere and the surface are the warmed up areas. The natural effect of greenhouse supports human life on earth, but the usage of green house gases have lead to global warming and increase in the greenhouse effect.
The greenhouse gases are primarily water vapour , carbon dioxide, methane, nitrous oxide and ozone. These gases contribute to global warming and greenhouse effect. CO2 is a greenhouse gas and is a primary reason for increase in global warming when released into the atmosphere. Emission of CO2 from various fuels and vehicles have contributed a lot to global warming. CO2 in the atmosphere allows solar radiation to pass to the surface of the earth and also energy is absorbed by Co2 and water vapor and acts as a blanket around earths atmosphere.
Water vapor accounts for largest % of greenhouse effect. Increase in water vapor concentrations is partially due to human activities and this is a major greenhouse gas.
Increase in carbon dioxide levels have increased radioactive forcing and this in turn have increased the warming of the atmosphere and the climate changes. Burning of fossil fuels are them major reason to this warming. This has caused a blanket over the earth and allows sunlight radiation to pass onto the earth.

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