Describe how Eratosthenes measured the circumference of our planet
What will be an ideal response?
Using the fact that the noon solstice Sun was directly overhead at Syene, on the Tropic of Cancer, yet was 7 degrees south of the zenith in Alexandria, Eratosthenes realized this was due to the curvature of the Earth, and that the 7 degrees was about 1/50th of the Earth's total circumference, so the Earth must be about fifty times larger in circumference than the 800 kilometer separation between Alexandria and Syene, or about 40,000 kilometers around.
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Pulsars were discovered because they _____
a. provide the energy to ionize supernova remnants b. radiate gravitational waves c. absorb matter from a binary companion through an accretion disk d. emit short, regular bursts of radiation e. undergo nova eruptions on a regular period of a few years
It takes Neptune a longer time to orbit the Sun than Earth does because Neptune
A) has much further to go. B) goes much slower. C) both of these D) none of these
If the wave function for a free electron is given by ? = A sin kx + B cos kx, and the electron has a kinetic energy of 9.0 eV, what is the value for k?
A) 2.5 x 109 m-1 B) 1.0 x 1010 m-1 C) 1.5 x 1010 m-1 D) 4.5 x 1016 m-1 E) 9.7 x 1017 m-1
Which of the following scientists is most directly responsible for ushering in the communications age in the 20th century?