OHM'S LAW

Radio Record, Volume I, Issue 26, 13 January 1928, Page 15

OHM'S LAW

FORMULA EXPLAINED,

The relation between voltage, current strength and resistance of a circuit is expressed by the law which was set forth by Ohm and this law is called Ohm’s law in his honour. "The strength of the current in amperes in any given circnit is directly proportional’ to the resistance of the circnit." ‘his is’ one of the most important Taws for a_ student of electricity or radio to know. ‘The formula, which can easily be rememberéd in the following form-amperes equals ‘yolts over ohhms-should be committed to memory, so that one can recite it backward. With this law it is. possible to find either one of the three values if the other two are known, and. because the formula is so simple it should be possible for any one to learn and use. Tt is learned from this law that to increase the amperage in a circuit containing resistance it is necessary to increase the voltage. ‘fhe correct increase may be easily figured out by using the above formula. With the aid of this formula it will be found that in a circuit containing three resistances in paraflel across the circuit that if each resistance has a different value a different amount of current will flow through each resistance, the smaller the resistance the greater the amount of current.

Units of Electricity. The practical units of electricity may be defined as follows: The practical unit of electromotive force is the volt . A volt is that pressure of electromotive force that is required to maintain a flow of current one ampere strong through a resistance of one ohm. The unit of current strength in an electrieal efrcuit is the ampere, which is explained as the strength of current maintained by a pressure of one volt! through a resistance of one ohm. The unit of resistance is the ohm. This is defined as the resistance of a conductor that permits the passage of current of one ampere at a pressure of one volt. The coulomb is the current qnantity flowing in a circnit when one ampere passes a given point in one secovd, The next unit of electrical measurement is the joule. The explanation of the joule is as follows: When a current of electricity flows through a conductor it encounters a certain amount of frictional resistance and some of the energy is turned into heat. This development of heat is proportional to the time the current flows to the square of the current and to the resistance of the conductor. ‘The unit joule is’ the amount of energy expended in heat during one second by a current of one ampere at a pressure of one volt through a resistance of one ohm. 746 Watts, one Horsepower. The joule per second is the practical unit of électrical power which has been named the watt. ‘the unit of power may be expressed in units of cerrent strength and pressure. ‘The power in watts in a given circuit in which a direct current is flowing is eaual to the product obtained by multiplying the current (ampercs) by tlc pressure (volts). To rate the power in watts of most motors or cther electrical devices would necessitate the use of figures that are too large for everyday. use, so the kilowatt i: uscd. A kilowatt is equal to 1000 watts. In mechanics a horsepower is equal to 83,000 foot pounds per minute, or, 550 foot pounds rer second . Jn electrical work the rating of motors mav be given in horsepower by finding the watt rating of the motor and dividing it by 746 watts. which is the electrical equivalent of 550 foot pounds, or one horsepower.