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Faraday's ice pail experiment is a simple electrostatics experiment performed in 1843 by British scientist Michael Faraday that demonstrates the effect of electrostatic induction on a conducting container. For a container, Faraday used a metal pail made to hold ice, which gave the experiment its name.〔John Ambrose Fleming, 〕 The experiment shows that an electric charge enclosed inside a conducting shell induces an equal charge on the shell, and that in an electrically conducting body, the charge resides entirely on the surface. It also demonstrates the principles behind electromagnetic shielding such as employed in the ''Faraday cage''. The ice pail experiment was the first precise ''quantitative'' experiment on electrostatic charge. It is still used today in lecture demonstrations and physics laboratory courses to teach the principles of electrostatics. ==Description of experiment== Below is a detailed modern description of the experimental procedure:〔〔〔〔 #The experiment uses a conductive metal container ''A'' open at the top, insulated from the ground. Faraday employed a 7 in. diameter by 10.5 in. tall pewter pail on a wooden stool,(B)〔 but modern demonstrations often use a hollow metal sphere with a hole in the top,〔 or a cylinder of metal screen,〔 mounted on an insulating stand. Its outside surface is connected by a wire to a sensitive electric charge detector. Faraday used a gold leaf electroscope, but modern demonstrations often use an electrometer instrument〔 because it is far more sensitive than an electroscope, can distinguish between positive and negative charge, and gives a quantitative readout.〔, p.4-5〕 The container is discharged by connecting it briefly to a large conducting object, called a ground (earth); this can be done by touching it with a finger, using the conductive human body as a ground. Any initial charge drains off into the ground. The charge detector reads zero, indicating that the container has no charge. #A metal object ''C'' (Faraday used a brass ball suspended by a nonconductive silk thread,〔 but modern experiments often use a small metal ball or disk mounted on an insulating handle〔) is charged with electricity using an electrostatic machine and lowered into the container ''A'' '' without touching it ''. As it is lowered the charge detector's reading increases, indicating that the outside of the container is becoming charged. Once the object is well inside the lip of the container the charge detector levels off and registers a constant charge, even if the object is lowered further. The charge on the outside of the container is the same polarity as that on the object. If the charge detector is touched to the inside surface of the container, it is found to be charged with opposite polarity. For example, if the object ''C'' has a positive charge, the outside of the container ''A'' will be found to have a positive charge, while the inside of the container has a negative charge. #If the object ''C'' is moved about inside the container without touching the walls, the charge detector's reading will not change, indicating that the charge on the outside of the container is not affected by where the charged object is inside the container. #If the charged object ''C'' is lifted out of the container again, the charge detector will decrease to zero again. This shows the charges on the container were induced by ''C'', and the container has no net charge. Therefore the opposite charges induced on the inside and the outside must be equal in size. #The charged object ''C'' is touched to the inside of the container. The charge detector reading does not change. However if the object is now withdrawn from the container, the reading stays the same, indicating that the container now has a net charge. If the object is then tested with the charge detector, it is found to be completely uncharged, and the inside of the container is also found to be uncharged. This indicates that all the charge on ''C'' has been transferred to the container, and has exactly neutralized the opposite charge on the inside surface of the container, leaving only the charge on the outside. So the charge on the inside of the container was exactly equal to the charge on ''C''. Kits are available from educational supply firms〔 containing all the apparatus needed for students to perform the experiment. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Faraday's ice pail experiment」の詳細全文を読む スポンサード リンク
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