8 26.2 The appearance of Plank' s constant h In 1901, Plank assumed that the energy e associated with the light inside the cavity was present only in finite packets(bundles proportional to the frequency v E=hy Where h was an unknown constant that he hoped to be able to set to zero after taking appropriate mathematical limits. h=6.626×10J.s It is a fundamental constant of nature. called by plank the quantum of action Now we called it plank’ s constant 826.3 The photoelectric effect 1. Apparatus and phenomenon a photocell is made by enclosing a metal plate and a collecting wire in an evacuated glass tube EM radiation(visible or 光电管 UVB) falls on the metal plate; some of the emitted electrons make = their way to the collecting g wire, which complete the circuit. An ammeter measures the current in the circuit 安培表9 §26.2 The appearance of Plank’s constant h In 1901, Plank assumed that the energy E associated with the light inside the cavity was present only in finite packets (bundles ) proportional to the frequency ν. E = hν Where h was an unknown constant that he hoped to be able to set to zero after taking appropriate mathematical limits. 6.626 10 J s 34 = × ⋅ − h It is a fundamental constant of nature, called by Plank the quantum of action. Now we called it Plank’s constant. §26.3 The photoelectric effect 1. Apparatus and phenomenon A photocell is made by enclosing a metal plate and a collecting wire in an evacuated glass tube. EM radiation(visible or UVB) falls on the metal plate; some of the emitted electrons make their way to the collecting wire, which complete the circuit. An ammeter measures the current in the circuit