A photocathode has a work function of 2.4 eV. The photocathode is illuminated with monochromatic radiation whose photon energy is 3.5 eV. The wavelength of the illuminating radiation is closest to:
A) 350 nm
B) 330 nm
C) 300 nm
D) 380 nm
E) 410 nm
A
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Suppose that Earth's ice caps melted, but everything else about the Earth's surface and atmosphere stayed the same. What would happen to Earth's average surface temperature?
A) The surface temperature would increase. B) The temperature would not be affected at all. C) The surface temperature would decrease. D) The surface temperature would change radically, until it was equal to the melting temperature of ice.
Briefly describe how human activity is affecting Earth's ozone layer
What will be an ideal response?
Given that the universe is about 14 billion years old, which of the following statements is logically valid?
A) All galaxies nearby us are about 14 billion years old. B) All galaxies that we can see are about 14 billion years old. C) All galaxies that we see have an age that is approximately equal to the age of the universe today, minus the lookback time (or light travel time) corresponding to the redshift of that galaxy. D) The oldest galaxies we see at great distances are younger than the oldest galaxies we see nearby.
Which of the beams is due to a positively charged helium nucleus?
A) a B) b C) c D) all of the above E) none of the above