What does UNIT JAR stand for? 

Unit Jar

A Leyden jar which is used as a unit of measure of charge.

It consists of a Leyden jar about 4 inches long and 3/4 inch diameter, with about 6 square inches of its outer and the same of its inner surface coated with tinfoil. It is placed between a source of electricity and a larger jar or battery of jars which is to be charged. The inner coating connects with the machine; the outer coating with the jars to be charged. Short conductors terminating in knobs connect with inner and outer coatings, and the knobs are adjusted at any desired distance apart.

By the charging operation the large jar or battery of jars receives a charge by induction, and the charge of the small jar is at first equal to this quantity. After a while a spark passes from knob to knob, discharging the small jar. This indicates the reception by the large jars of the quantity of electricity represented by the charge of the small jar. The charging goes on, and for every spark approximately the same quantity of electricity is received by the larger jars.

The sparking distance m is directly proportional to the quantity of electricity, and inversely proportional to the area of coated surface, or is proportional to the potential difference of the two coats. This is only true for short sparking distance, hence for accuracy the knobs should be adjusted not too far from each other.

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