Re: Power Measurent: Watts Vs. Volts

Kaimbridge wrote:


> For instance, "Danger, Keep out: 50,000 volts!" (or just "High
> Voltage"). Static electricity can zap you with 50,000 volts, and
> you'll just feel a snap--Why?: Because there is very little amperage,

No, the current is determined from the voltage and resistance (body
resistance and ground resistance in series) by Ohms law R = U/I. But in
the case of static electricity the current will stop immediately,
because the capacity of the "power source" is extremly low.

> Similarly, product "letter" batteries (A, AA, AAA, C, D) are all
> measured as "1.5 volts" (I believe 2 equal 3 volts, 4 equal 6,
> etc.--?). Don't the batteries have a defined amperage (maybe that's
> the difference between A and AA and C, etc.?), thus why aren't they
> defined as "___watt" batteries (if the amperage--and therefore the
> wattage-- decreases as the battery weakens, its defined value would be
> its full, maximum strength)?

Again current is determined by Ohms law. There are two main differences
between a C battery and an AAA: Capacity and internal resistance. A
battery converts chemical into electrical energy, a C battery has more
of the chemicals and hence can sustain a given current for a longer
time. In addition, its electrodes are bigger, hence internal resistance
is lower. The voltage across a battery is determined by the kind of
chemicals used inside, for example Zn/C = 1.5 V.

> Finally, radio signal strength: Why is it measured as "microvolts" and
> not "microwatts", especially since a station's transmitter output power
> *is* measured in wattage?

The field strength is V/m, this will result in a certain voltage across
the poles of an antenna. Given the antennas resistance (usually 220 or
75 Ohm) this will result in a certain power, since R = U/I and P = U*I
the power is P = U^2/R.

A good high school physics textbook will cover these fundamentals in
more detail.
.

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