The effect of all known electrical appliances is due to the electrical energy. As a result, we get light, heat, sound, mechanical motion, that is, different types of energy. In this article, we will discuss and explore such physical concepts as the power of an electric current.

Formula power supply

Under the current capacity in the same way as in mechanics, understand the work that is performed per unit time. To calculate power, knowing the work that carries the electric current for a certain period of time will help the physical formula.

Formula power supply

Current, voltage and power in electrostatics associated with equality, which can be derived from the formula A = UIt. It determines the work done by electric current:

P = A/t = UIt/t = UI
Thus, the formula for DC power on any part of the circuit is expressed as the product of the current on the voltage between the ends of the plot.

The units of power

1 W (watt) - current power of 1 A (ampere) in a conductor, between the ends of which a voltage of 1 V (volt) is maintained.

A device for measuring electric current power is called a wattmeter. Also formula power current allows to determine the power with a voltmeter and ammeter.

Off-system unit power – kW (kilowatt) to GW (gigawatt), mW (milliwatt). this is related and some non-si units of measurement, often used in the home, for example (kilowatt·hour). Since 1 kW = 10 3 watts and 1 hour = 3600с. it

1kW·  h = 10 3 W · 3600s = 3.6 · 10 6 W · s = 3.6 · 10 6 J.

Ohm's law and power

Using Ohm's law, formula power supply P = UI written in this form:

P = UI = U 2 /R = I 2 /R
Thus, the power allocated to the conductors, directly proportional to the current flowing through the conductor, and the voltage at its ends.

Actual and nominal power

When measuring the power of the consumer formula of power supply allows to determine its actual value, that is the one that really stands out in a given time by the user.

In passports of various electrical appliances also note the value of the power. It is called nominal. In the passport of the electric appliance is usually indicated not only nominal power, but the power for which it was designed. However, the voltage may be slightly different from the one in the passport, for example, increase. With the increase in voltage increases the current in the network, and hence the capacity of the current consumer. That is, the value of the actual and the nominal power of the device may vary. The maximum actual capacity of the electric devices is larger than the nominal. This is done to prevent the failure of the device with little voltage variations in the network.

If the circuit consists of multiple consumers, then calculating their actual capacity, it should be remembered that any connection of consumers is the total power in the whole circuit equals the sum of the capacities of individual consumers.

The efficiency of the electric appliance

As you know, the ideal of machinery and mechanisms do not exist (that is, those that have fully converted one form of energy to another, or would generate energy). During operation of the device a necessary part of the energy is spent on overcoming the unwanted forces of resistance or simply "scatters


A physical quantity that shows which part of the useful work expended is called the efficiency (more efficiency).

In other words, efficiency shows how efficiently the spent work is used when it is performed, for example, by an electrical device.

Efficiency (denoted by the Greek letter

Efficiency is determined (as in mechanics) by the formula:

If you know the power of an electric current, the formula for determining the CCC would look like this:

Before determining the efficiency of a certain device, it is necessary to determine what is useful work (which created the device), and what is spent (work in progress, or what energy is spent performing useful work).

A conventional electric bulb has a power of 60 watts and an operating voltage of 220 V. What kind of work does the electric current in the lamp, and how much you pay for electricity during the month, at the rate T = 28 rubles, using the bulb 3 hours every day?
  What is the current strength in the lamp and the resistance of its spiral in working condition?

1. To solve this problem:
a) calculate the operating time of the lamps during the month
  b) we calculate the work of the current in the lamp;
C) computed cost per month at the rate of 28 rubles
g) calculate the current in the lamp
  d) calculate the resistance of the spiral lamp in working condition.

2. The work current is calculated according to the formula:

The strength of the current in the lamp will help to calculate the formula power current:

The resistance of the spiral lamp in working condition from Ohm's law equals:

[I] = 1B·1A/1V = 1A

t = 30 days · 3 h = 90 h;
A = 60·90 = 5400 W·h = 5,4 kW·h
  I = 60/220 = 0.3 A;
  R = 220 / 0.3 = 733 Ohm;
  B = 5.4 kW · h · 28 k / kW h = 151 rubles.

Answer: A = 5.4 kWh; I = 0.3 A; R = 733 Ohm; B = 151 ruble.

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