What do wind turbines, hydroelectric dams, and ethanol plants have in common?

a. all produce electrical current with pollution
b. all use generators to produce electrical current
c. all convert gravitational potential energy to electrical current
d. all convert thermal energy to electrical current

Glass is transparent to visibile light under normal conditions; however, at extremely high intensities, glass will absorb most of the light incident upon it. this works through a process known as multiphoton absorption. in this process, several photons are absorbed at the same time. if very intense light whose photons carry 2ev of energy is shined onto a material with a band gap of 4ev, that light can be absorbed through two-photon absorption, because two photons have the right amount of energy to bridge the band gap. what is the minimum number of photons of 800-nm light that are needed to equal or exceed the band gap of fused silica glass

If a simple machine reduces the strength of a force, what must be increased?

You've already seen the value of 9.8 in this lesson. what's this value called? what quantity does it represent?