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#1
December 13th 10, 07:42 PM
posted to rec.radio.amateur.antenna
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antenna physics question
On Dec 13, 7:32*pm, Registered User wrote:
On Mon, 13 Dec 2010 18:02:55 -0000, wrote: Registered User wrote: On Mon, 13 Dec 2010 00:13:10 -0000, wrote: Registered User wrote: On Sun, 12 Dec 2010 17:32:53 -0000, wrote: Registered User wrote: Efficiency is a measure so it must have one or more dimensions Efficiency is a ratio usually expressed as a percentage and has no dimensions. The efficiency of an antenna is the radiated power divided by the input power. There are two dimensions in the calculation, radiated power and input power. Although the units of measure associated with the dimensional data may cancel the dimensional metadata doesn't. x power/ y power = x/y The units cancel to form a dimensionles, unitless, ratio. This is grade school math. unitless yes and in the example given no metadata is provided. The result of the calculation is just a meaningless number. What of the equation : * * x units of radiated power / y units of input power The units cancel but the metadata doesn't. The result is a number that describes the ratio of radiated power to input power. 2 watt / 10 watt = 0.2 No "metadata". Yes no metadata beyond the UOM and when the UOMs cancel the result is a bare number. Twenty percent of what? If the 2 watts is the radiated power of an antenna and the 10 watts is the input power, the antenna efficiency is 0.2 or 20% since efficiency is normally expressed as a percentage. Now you're adding metadata to provide information about what the 0.2 or 20% means. If the 2 watts is the output power of some circuit and the 10 watts is the input power, the circuit has a gain of 0.2 or -7db. If the input energy to a heat engine is 10 joules and the output energy is 2 joules, the efficiency of the engine is: 100 * (2 joule / 10 joule) = 20% A selected calculated expression provides a ratio which resolved to a value of three-tenths. Which of the three previously shown expressions, if any, was selected to produced the result 0.3? A - antenna efficiency B - engine efficiency C - circuit efficiency D - none of the above It's a simple question with no metadata provided about the calculated expression arguments and no metadata associated with the result. In a nutshell, no metadata what so ever. If metadata is unimportant then there should be no problem answering the question. the answer is 42 |
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