The Metonic cycle is
A) used to keep lunar calendars approximately synchronized with solar calendars.
B) used to predict the future orientation of the Earth's axis in space.
C) the ancient Greek name for the cycle of lunar phases that repeats every 29 1/2 days.
D) the 18-year, 11-day period over which the pattern of eclipses repeats.
A
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Weight and g: At a given point above Earth's surface, the acceleration due to gravity is equal to 7.8 m/s2. What is the altitude of this point above Earth's surface? (G = 6.67 × 10-11 N ? m2/kg2, Mearth = 5.97 × 1024 kg, Rearth = 6.38 × 106 m)
A. 770 km B. 970 km C. 1500 km D. 2000 km E. 2400 km
How does the slope of the graph in Procedure 1 compare with the average value of C d?
Magnifying Glass With the Image at Infinity: What is the angular magnification of a magnifying glass of focal length 4.0 cm if the image is to be viewed by a relaxed eye having a near point of 25 cm?
A. 2.0 B. 3.0 C. 3.6 D. 4.0 E. 6.3
A filament of tungsten wire is 0.001 m in diameter, and the filament is heated to 2500 K. The work function of tungsten is 4.5 eV.
(a) Calculate the probability of electrons having sufficient energy to be emitted from the filament. (b) Calculate the emission current density from the tungsten wire. (c) What length of wire can produce a thermionic electron current of 1 A?