1. A current flowing through you of more than 5ma is considered dangerous. Why do we see...
Question:
1.A current flowing through you of more than 5ma is considered dangerous.
Why do we see warnings about high voltage, rather than highcurrent?
What voltages are dangerous even if the skin is dry? (Dry skinhas a resistance of 100 kohms while wet skin can be much less.)
An electroencephalogram (EEG) is a recording of differences involtage observed on the scalp by attaching electrical contacts. Ifvoltage differences that are observed are about 0.5 mv, and theresistance of the skin is about 10 kohms, what size currents areinvolved?
2.Suppose you fall from a building and on theway down you grab a high voltage wire. Assuming that the wire holdsyou, will you be electrocuted? If the wire breaks, should youcontinue to hold on as you fall?
3. A cloud can discharge as much as 20 coulombsin a lightning bolt. If the bolt lasts only 0.1 msec, how many ampsis that?
4. Imagine a copper wire 10 km long that needsto supply a city with 10 Mwatts of power--say from a waterfall. Ifthe city ran on DC power, with voltages of 100 V, how much currentwould run through that wire? If you were willing to lose 1% of yourpower as heat in the wire, how thick would such a wire have to be?The resistivity of copper is 1.7 x 10-8 W-m.
5.Which has greater resistance: a 75 watt bulbor a 100 watt bulb?
Suppose you connect a 75 watt bulb across only 50 volts: willyou still get 75 watts of power?
Suppose you connect a 100 watt lamp and a 75 watt lamp in seriesand then connect the combination to a regular 110 volt line. Whichlamp (if either) will burn brighter?
(note that we are talking about incandescent bulbs here... thenewer types are quite different.)
Income Tax Fundamentals 2013
ISBN: 9781285586618
31st Edition
Authors: Gerald E. Whittenburg, Martha Altus Buller, Steven L Gill