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VICPhysicsQuick questions

Unit 1: How is energy useful to society?

Quick questions on The greenhouse effect and climate: VCE Physics Unit 1 Year 11

14short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is solar constant?
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Approximately 1370 W mβˆ’2^{-2} at Earth's mean orbital distance. This is the energy flux through a surface perpendicular to the sun at the top of the atmosphere.
What is average flux at Earth's surface?
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Earth intercepts solar power on a cross-section Ο€R2\pi R^2 but distributes it over a surface area 4Ο€R24 \pi R^2. So the average flux at the surface (before atmospheric effects) is 1370/4β‰ˆ3421370 / 4 \approx 342 W mβˆ’2^{-2}.
What is planetary albedo?
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Earth reflects about 30 percent of incoming solar radiation (clouds, ice, deserts). Albedo β‰ˆ0.30\approx 0.30. The absorbed fraction is 0.700.70, giving about 240 W mβˆ’2^{-2}.
What is radiative equilibrium?
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In equilibrium, Earth emits as much energy as it absorbs. Use Stefan-Boltzmann (P/A=ΟƒT4P/A = \sigma T^4) to find the effective radiating temperature: Teffβ‰ˆ255T_{\text{eff}} \approx 255 K (or βˆ’18-18 degrees C).
What is solar?
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Photovoltaic (PV) cells convert sunlight directly to electricity (photoelectric effect at semiconductor band gaps). Efficiency 15 to 25 percent for commercial silicon PV.
What is wind?
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Kinetic energy of wind converted by turbines. Power ∝ρAv3\propto \rho A v^3 (proportional to cube of wind speed). Wind farms produce 20 to 50 percent of theoretical maximum (Betz limit 59 percent).
What is hydro?
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Gravitational potential energy of water converted by turbines.
What is nuclear?
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Already discussed. Low CO2 emissions but waste and safety concerns.
What is geothermal?
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Earth's internal heat (largely from radioactive decay in mantle).
What is battery storage?
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Critical for intermittent renewables. Lithium-ion is current dominant technology.
What is linear extrapolation of warming?
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Climate response is non-linear due to feedbacks. The simple Stefan-Boltzmann argument captures only the direct response.
What is q1?
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Distinguish between the natural and the enhanced greenhouse effect. [2 marks]
What is q2?
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A planet with surface temperature 290290 K has albedo 0.300.30. Calculate (a) the power per square metre radiated by the surface, and (b) the absorbed solar power per square metre if the solar constant is 13611361 W mβˆ’2^{-2}. [4 marks]
What is q3?
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Refer to the Melbourne urban heat island. (a) Outline the role of albedo in surface temperature. (b) Calculate the increase in radiated power per square metre when a roof warms from 30∘30^\circC to 50∘50^\circC.

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