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Si presenta una nuova tecnica calorimetrica per la determinazione della costante di Stefan-Botzmann alla temperatura del ghiaccio fondente. La tecnica non. (s) For a discussion of the experimental verification of Planck's law, see also L. .. della costante di Stefan-Boltzmann alla temperatura del ghiaceio fondente. This file has an extracted image: File:Boltzmann posavski-obzor.info Extracted Ludwig Boltzmann · Costante di Boltzmann · Viaggio nel tempo.
Photoelectric effect The photoelectric effect is the emission of electrons called "photoelectrons" from a surface when light is shone on it. It was first observed by Alexandre Edmond Becquerel inalthough credit is usually reserved for Heinrich Hertz who published the first thorough investigation in Another particularly thorough investigation was published by Philipp Lenard in The energy transferred by a wave in a given time is called its intensity.
The light from a theatre spotlight is more intense than the light from a domestic lightbulb; that is to say that the spotlight gives out more energy per unit time and per unit space and hence consumes more electricity than the ordinary bulb, even though the colour of the light might be very similar.
Boltzmann constant - Wikipedia
Other waves, such as sound or the waves crashing against a seafront, also have their own intensity. However, the energy account of the photoelectric effect didn't seem to agree with the wave description of light. The "photoelectrons" emitted as a result of the photoelectric effect have a certain kinetic energywhich can be measured.
This kinetic energy for each photoelectron is independent of the intensity of the light,  but depends linearly on the frequency;  and if the frequency is too low corresponding to a photon energy that is less than the work function of the materialno photoelectrons are emitted at all, unless a plurality of photons, whose energetic sum is greater than the energy of the photoelectrons, acts virtually simultaneously multiphoton effect.
Planck constant - Wikipedia
The size of these "packets" of energy, which would later be named photonswas to be the same as Planck's "energy element", giving the modern version of the Planck—Einstein relation: I n fact, all the radiation e m i t t e d b y the b l a c k - b o d y aperture, even if p a r t i a l l y diffracted, contributes w i t h o u t losses to the sample cooling. This is essentially t h e s a m e one employed 9 for m e t a l emissivity studies, the only difference being in t h e f o r m of t h e sample.
A few milliwatt of radiation f r o m a H e - N e laser is shone f r o m the exterior on the cylinder t h r o u g h two prisms. At the b o t t o m of the cylinder a copper disc is suspended b y m e a n s of similar silk threads. This disc constitutes t h e top wM1 of a cylindrical resonant c a v i t y excited at 25 G I t z in the TE01 mode. Since for t h e TE01n modes no current flows between t h e t e r m i n a l walls and the sides of the cylinder, no electrical contact between t h e disc a n d the cylinder is required for t h e working of t h e cavity.
Another identical resonator whose top wall consists of a piston is used as a reference. I n order to detect and to record t h e change in t h e r e s o n a n t frequency of the cavity, caused b y the expansion of the cylindrical sample, a technique is used which was previously developed b y BATTAGLIA et al.
I t is, therefore, possible to record the evolution of t h e sample t e m p e r a t u r e almost in conditions of t h e r m a l equilibrium with the eha.
Equazione di Butler-Volmer
I n order to minimize t h e r m a l drifts, which affect t i m e constant deter- minations, b o t h microwave cavities are set, in the present experiment, in the same b a t h of m e l t i n g ice, whose t e m p e r a t u r econtrolled with a quartz t h e r m o - meter, r e m a i n s constant for a few hours within -2 K.
I n the cylindrical top surface a circular aperture of 1. This aperture can be closed b y means of a cap made of the same copper foil used for t h e cylindrical walls, as shown in fig.
First of all we verified t h a t the decrease of t h e sample temperature, during the cooling process, followed an exponential law see fig.
This allowed us to conclude t h a t the t h e r m a l gradients on the cylinder surface were negligible. This is in agreement with the considerations reported in the appendix.
The evaluation of the sample heat capacity involves an u n c e r t a i n t y t h a tin fact, produces the largest u n c e r t a i n t y in the present preliminary determination of the Stefan-Boltzmann constant.
This limit is actually not an intrinsic one for t h e present method, b u t is rather related to t h e fortuitous circumstance t h a t in our laboratory no high-accuracy calorimeter was available.
W e gratefully acknowledge t h e assistance of E. I n our case, as is show in fig.
I f we assume t h a t the inner surface of the c a v i t y of emissivity c has a constant t e m p e r a t u r e T and is a perfectly diffusing gq: