When the time of exposure is doubled:
The number of photons generated is doubled
The energy of photons generated is doubled
The velocity of photons is doubled
The mass of photons is doubled
EXPOSURE TIME (s):
Changing the exposure time—typically measured in fractions of a second (s)—modifies the duration of the exposure and thus the number of photons generated. When the exposure time is doubled, the number of photons generated at all energies in the X-ray emission spectrum is doubled. The range of photon energies is unchanged.