E2=- 13.6/4ev=-3.4ev

When n=2, the energy △E required for hydrogen atom to transition from ground state to steady state.

△E=E2-E 1= 10.2ev

Under the irradiation of visible light, this transformation will not happen.

The photon of reason E= 10.2ev is in the ultraviolet region.

Constant, a mathematical term, refers to a specified quantity and number, such as the ratio of the circumference to the diameter of a circle π, and the expansion coefficient of iron is 0.0000 12. Constant is a name with a certain meaning, which is used to replace numbers or strings, and its value never changes. In mathematics, the capital letter "c" is usually used to represent a constant. And generally classified as transcendental numbers (such as π, σ 10-j! ), irrational numbers (such as e and φ), uncountable numbers (such as√ 2 and ω u) and computable numbers (such as δ and γ).