ISBN: 9781154907902

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustra… More...

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1897 Excerpt: ...equivalent of one watt. As one heat unit equals 778 foot-pounds, 1 foot-pound is yj of a heat unit, and.75 of a footpound.75 X =.00096. This means that 1 watt, in 1 second, will heat a pound of water.00096, and may be considered as the heat equivalent of a watt in a second. From Ohm''s Law we have E--CR. If this value of E be substituted for the E in EC, which represents electrical energy, we shall have OR X C= CPR as an equivalent expression for electrical energy in terms of current and resistance. It shows that the energy or heating power is proportional to the square of the current, and this must be remembered. Two amperes will heat 4 times as much as 1, and 10 amperes 100 times as much, and so on. If the resistance be doubled, the heat will be doubled, that is, the heating is proportional to the resistance. It might be supposed that if the current was maintained for 2 seconds, it would develop twice as much as it would in 1 second, and in t seconds t times as much. Putting all these factors together, the amount of heat developed is equal to.00096 X A For instance, how much heat would be developed in 1 minute by a current of 10 amperes in a wire having 3 ohms resistance?.00096 X 102 X 3 X60 = 17.28, or 1 pound of water would be heated 17.28 by it. An apparatus suitable for studying the heating power is shown in the adjacent figure (49). It is a bottle for holding a known quantity of water, through the cork of which is fixed a coil of wire of known resistance, submerged in the water; a thermometer extends into the water, on which the rise in temperature may be observed during the passing of the current. The temperature to which a given body will be raised by a definite amount of heat depends upon its specific heat (p. 92). As water has the highest specific... Amos Emerson Dolbear, Books, Fiction and Literature, Fiction, First principles of natural philosophy Books>Fiction and Literature>Fiction <