Force of electric current is measured in amperes. Therefore to calculate amperes, it is necessary to find this physical quantity. Current can be measured by a tester. If there is no such opportunity, it is possible to recognize current in a chain or the specific consumer by the law of Ohm.
It is required to you
- - tester;
- - documentation on consumers;
- - current source.
Instruction
1. To find amperes which measure current use the usual tester adjusted for measurement of this size. Include it in a chain consistently with consumers. On the display the value of current will appear. If the tester is ready for multiple or submultiple sizes, use rules of their transfer to usual. For example, if the device in a chain shows current 120ma, then divide this number into 1000 and receive value 0.12 A. If current is equal to 2.3 kA, then now increase value by 1000 and receive 2300 A.
2. If to measure current there is no opportunity, find it on tension which is necessary for work of the consumer and to his electrical resistance (Ohm's law for subcircuit). For this purpose tension on this site of a chain of U divide R (I=U/R) into its resistance. For example, if in household network the iron with a resistance of 160 Ohms is connected, then current in it is equal to tension relation (in household network it equally to 220 V) to resistance of I=220/160=1.375 A.
3. To determine current in a chain, without measuring tension on the consumer, learn the EMF (electromotive force) of a source of current and its internal resistance. Determine chain resistance. Find current, having divided EMF into the sum of internal resistance of a source of r and external resistance of R (I= EMF (/R+r)). For example, if the lamp is connected to the accumulator with the EMF of 12 V, and has resistance of 20 Ohms, and internally accumulator resistance equally in 4 Ohms, then current will be equal in a lamp to I=12/(20+4)=0.5 And.
4. On some devices, for example lamps, their power is specified with a rated voltage. Determine the nominal current which proceeds on such device, P power relation to the rated voltage of U (I=P/U). For example, if on a lamp it is specified, 100 W, 220 V, then the current proceeding on it will be equal to I=100/220? 0.45 A.