A hydrogen atom that has an electron in the n = 2 state absorbs a photon. What wavelength must the photon possess to send the electron to the n = 4 state?

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

What is the speed of an object at a given moment?

Give one example to show that when substances are mixed,it may result in a chemical or a physical change depending on the conditions.