ACT Science Practice Question #1831 (Hard (600)) | Test Citadel
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ACT Science Difficulty: Hard (600)

Digital ACT Science Practice Question #1831

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How can Star 4 (Sirius B) possess an extremely hot surface temperature of 25,000 K while radiating a luminosity of only 0.003 L_sun? Experiment Context (Hertzsprung-Russell Stellar Data): Astrophysicists surveyed four representative stars, compiling surface temperatures (in Kelvin) and luminosities relative to the Sun (L_sun = 1.0): Table 26: - Star 1 (Betelgeuse): Surface Temp = 3,500 K; Luminosity = 100,000 L_sun; Spectral Class = M - Star 2 (Sun): Surface Temp = 5,800 K; Luminosity = 1.0 L_sun; Spectral Class = G - Star 3 (Sirius A): Surface Temp = 9,900 K; Luminosity = 25 L_sun; Spectral Class = A - Star 4 (Sirius B): Surface Temp = 25,000 K; Luminosity = 0.003 L_sun; Spectral Class = DA
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Tiny radius (white dwarf) yields low luminosity despite high temperature.

Masterclass Solution & Distractor Trap Analysis

Stefan-Boltzmann law: L = 4*pi*R^2 * sigma * T^4. To have tiny L with huge T, radius R must be minuscule....

Distractor Analysis: Trap choice eliminates careless test-takers who confuse roots with coordinates...

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