Which of the following is true about all electromagnetic waves in a vacuum?
a. they all carry the same energy.
b. they all travel at the same speed.
c. they all have the same frequency.
d. the all have the same wavelength.

How does a sample of helium at 15 degree celsius compare to a sample of helium at 215 k? a) the helium at 15 degrees celsius has a higher average kinetic energy that the sample at 215 k. b) the helium at 15 degrees celsius has lower nuclear energy that the sample at 215 k. c) the helium at 15 degrees celsius has slower- moving atoms that the sample at 215 k. d) the helium at 15 degrees celsius has smaller atoms than the sample at 215 k.