A metal having a work function of 2.4 eV is illuminated with monochromatic light whose photon energy is 4.0 eV. What is the maximum kinetic energy of the photoelectrons produced by this light? (h = 6.626 × 10-34 J • s, 1 eV = 1.60 × 10-19 J)
A) 2.6 × 10-19 J
B) 3.8 × 10-19 J
C) 4.7 × 10-19 J
D) 5.5 × 10-19 J
E) 6.4 × 10-19 J
A
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Potassium-40 decays into daughter isotopes with a half-life of _____
A) 1.25 billion years B) 1.5 billion years C) 1.75 billion years D) 2 billion years
When astronomers first saw the spectrum of a quasar they did not recognize it because
a) the lines were so far shifted towards the red b) its spectral signature was masked by the presence of the central supermassive black hole c) the chemical elements present in a quasar were unfamiliar d) the lines were so far shifted towards the blue e) it was too faint to produce spectral lines of any sort
Ellen says that whenever the acceleration is directly proportional to the displacement of an object from its equilibrium position, the motion of the object is simple harmonic motion. Mary says this is true only if the acceleration is opposite in direction to the displacement. Which one, if either, is correct?
A. Ellen, because ?2 is directly proportional to the constant multiplying the displacement and to the mass. B. Ellen, because ?2 is directly proportional to the mass. C. Mary, because ?2 is directly proportional to the constant multiplying the displacement and to the mass. D. Mary, because ?2 is directly proportional to the mass. E. Mary, because the second derivative of an oscillatory function like sin(?t) or cos(?t) is always proportional to the negative of the original function.
You leave a black, spherical bowling ball out in the hot sun and it warms to a scalding hot temperature of 80ºC. The ball has a radius of 0.25 m (25 cm). What is the total power being radiated outward from this hot ball at this temperature?