Which variable would be most useful in determining the number of people eligible for retirement benefits in a certain year?
a. birthrate
b. death rate
c. growth rate
d. age structure

Modern physics a photon emitted from an excited hydrogen atom has an energy of 3.02 electron volts. which electron energy-level transition would produce this photon? a. n=1 to n=6 b. n=2 to n=6 c. n=6 to n=1 d. n=6 to n=2 i chose b but the correct answer is d can someone tell me why? and what's the difference?

Find the magnetic field a distance r from the center of a long wire that has radius a and carries a uniform current per unit area j in the positive z direction.

In science and physics what is the standard unit of measure for speed?