| From: | JmW |
| Date: | 1 Feb 2000 at 11:48:33 |
| Subject: | RE: Re: 'O'-level physics (was "PFS3") |
From: "JmW" <John@wasilewski.co.uk>
-----Last Message-----
From: Michael Bourne [mailto:michael@veil.circleware.org]
> From: "Michael M. Rye" <mrye@execpc.com>
>> From what I remember, lightning strikes are high _voltage_ ,
> not high amperage.
To put it simply:
It's both. A very high voltage is required initially to ionize the
air but the current which then flows is very high indeed, as
stated.
Its current (rate of flow) that vaporizes copper etc not voltage...
that's just "pressure" and does nothing but, by analogy, "push" the
coulombs/sec (amperes) through whatever the conducting medium
happens to be.
-----Comment by JmW-----
Sorry, chaps, I can't resist the urge to intervene in this erudite debate.
MB was right in his assertion that "its both," and he earned quite a few
marks by his "pressure" analogy. However, as every - erm - /civil/ engineer
knows, MB then lost marks in claiming that the current does the work.
It is NOT the "pressure" (voltage).
It is NOT the "flow rate" (current).
It is the POWER (no analogy).
Direct current
POWER (watts) = VOLTAGE (volts) x CURRENT (amps)
For Alternating current, the same applies exceptht hat it varies
continuously so it is usually averaged over the AC cycle. AFAI can
remember, a typical sinusoidal AC cycle has
Avge POWER = 2/3 x (PEAK Voltage) x (PEAK current).
And in case anyone is in any doubt about it, although the ultimate bearing
capacity of a driven or bored pile in building foundations equals the sum of
the total shaft resistance and the total end-bearing capacity, the two
components are not mobilised in equal proportions under normal service
loading.
John Wasilewski
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