SAT Subject Physics Practice Question 164: Answer and Explanation
10. Which principle could be used to help calculate the amount of radiation emitted by a star?
A. Newton’s law of universal gravitation
B. Red shift of light from other galaxies
C. The fact that every element of atomic number greater than 83 is radioactive
D. The zeroth law of thermodynamics
E. Mass–energy equivalence
Correct Answer: E
Stars are huge nuclear-fusion reactors. When nuclei fuse, the mass of the product nucleus is less than the combined masses of the original nuclei. The “missing” mass has become energy, which is radiated away. Einstein’s famous mass-energy equivalence equation, E = mc2, can be used to calculate the amount of energy resulting from a fusion reaction.