In each closed circuit, double conversion of energy takes place without fail. In the current source, some energy is modified (for example, in the generator - mechanical) into electrical energy, and in the current circuit it again turns into an equivalent amount of energy of a different kind. The measure of the transformation in the current circuit of electricity into any other types of energy is the magnitude of the current.
But we understand that the work and power of electric current is the work of electric field forces moving charges; therefore, it is easy to calculate.
The work of transferring an electric charge in an electric field is estimated by the product of the value of the transferred charge by the value of the potential difference between the points at the beginning and end of the transfer, i.e. voltage value:
A = qU.
Obviously, this ratio can also be applied to evaluate concepts such as work and electric current power. The magnitude of the charge flowing in the circuit, we can judge by the current flowing in the circuit, and the time of its flow, since q = It.
Using this ratio, we obtain a formula expressing the magnitude of the current in a separate section of the circuit having a voltage U:
A = UIt.
The work and power of the electric current are measured as follows: if you measure the current in amperes, the operating time in seconds, and the voltage in volts, then the work is in joules (J).
So 1 joule = 1 amp x 1 volt x 1 second.
Power is measured in watts (W):
1 watt = 1 joule / 1 second, or 1 watt = 1 volt x 1 amp.
The question of calculating the magnitude of the current in this section is completely unrelated to the question of what type of energy will turn into electric energy in this section. This work is a measure of electricity converted into other types.
While carrying out work, an electric current can glow the filament of an electric lamp, melt metals, rotate the armature of an electric motor, cause chemical transformations, etc. In all cases, the work and power of the electric current determine the level of conversion of electricity into other forms - mechanical energy, energy of thermal motion, etc.
Knowing that the power is P = A / t, we can obtain a formula with which the current power is calculated on a separate section of the circuit:
P = UI.
Work and DC power can be calculated using these formulas, as well as using an ammeter, voltmeter. In practice, the electric field is measured by a special device - a counter. Passing through the counter, a light aluminum disk begins to rotate inside it , and its rotation speed will be directly proportional to the current strength and voltage. The number of revolutions that he will make in a certain time will help to draw conclusions about the work completed during this time. Electricity meters can be seen in every apartment.
The current power is measured using a special device - a wattmeter. The device of this device combines the principles of a voltmeter and an ammeter.
Many electrical appliances and technical devices indicate their power. For example, the power of an incandescent bulb can be 25 W, 75 W, etc., the power of a vacuum cleaner or iron is about 1000 W, the power of electric motors can reach very large values ββ- up to several thousand kilowatts. At the same time, they mean the power of the current that passes through one or another device.
Operation and AC power are calculated differently. So, to calculate the work done by alternating current for a certain period of time, you can use the formula:
P = 1 / 2IβUβ cos Ο. Often this formula is written in the following form: P = IU cos Ο, where I and U are the voltage and current values, which are 2 times less than the corresponding amplitude values.
The formula for calculating AC power will be the same as for DC.
Units of energy and work:
1 watt-second = 1 J; 1 watt-hour = 3600 J;
1 hectowatt-hour = 360,000 J;
1 kilowatt-hour = 3600000j.
Power Units:
1 ampere-volt = 1 W;
1 hectowatt = 100 W;
1 kilowatt = 1000 watts.