The strength of the current represents the movement of charged particles in a certain direction, in the taken conductor. Many physicists in the past were worried about the question: what is the current measured and how to measure what is invisible and intangible. But thanks to a number of discoveries, the situation began to become clearer. In order for the movement of charged particles to appear, the action of an electric field is needed.
Content
- Units
- Different values
- Power measurement
- Frequency definition
- Practical use
At the same time, charged particles appear constantly, due to tight contact in any substance:
- conductors
- semiconductors
- dielectrics.
Charged particles are capable of free movement in different directions. Materials where charged particles move freely are called conductors: metal, salt solutions.
Materials where electrical particles cannot move are called dielectrics: gas, quartz, wood.
Materials that have not only electronic, but also "hole" conductivity, which depends on many external factors (light, temperature, magnetic and electric fields) are called semiconductors: selenium, silicon, germanium.
Units
The current is subdivided into several types. The main ones are presented as follows:
-
Constant - meaning and direction do not change over time; - Sinusoidal - the value changes according to the sinusoidal law;
- High-frequency - the frequency starts from tens of kilohertz;
- Periodic - the values of which are repeated in time with the same frequency;
- Pulsing - periodically changing a value in time, other than zero.
Scientists have often wondered in what units the current strength is measured. For measurement, use a physical quantity. This physical quantity is equal to the ratio of the value of the charge Q, which has flowed through the cross-section of the conductor for some time, to the value of this time period: I = Q / t. And it is measured in amperes and shows the designation of the current strength: A.
The electric current is measured in what it is calculated in - on schematic diagrams. This definition helps to calculate power supplies of a certain power.
In electrical circuits, indicators are calculated according to Ohm's law, and this is what answers the question of what the current is. Force I at a certain section of the circuit is directly proportional to the voltage supplied to it and is inversely proportional to the resistance R of the section of the circuit: I = U / R.
Different values
If there is an alternating current in the section of the circuit, the voltage is constantly changing, so if we take the average voltage values, then they will be equal to zero, and the average power will not be equal to zero. For this, the following concepts began to be used:
- instantaneous values;
- amplitude values;
- effective values.
Instantaneous values are those that occur at a given moment in time. Amplitude values are the highest. The effective values are determined by the thermal property of the current flowing through the cross-section of the conductor, and the direction of the vector value coincides with the directions of movement of positive particles.
For accurate measurements, basic parameters are needed: voltage, power, resistance, frequency.
Power measurement
Power is called a certain amount of work that is done in one second of time.
To measure power, the unit was adopted - watt.
Therefore, a power of 1 W is called a power of 1 A with a voltage value of 1 V.
In order to calculate the power, you need to multiply the current by the voltage.
If the power is denoted by the letter P, then the formula will take the form:
P = I * U.
Power is calculated using resistance. The amperage and resistance of the circuit are often known, but the voltage is usually unknown.
Therefore, using Ohm's law:
U = IR
we get the formula: P = I2* R
Frequency definition
The movement of electrons in a conductor in one direction and then in the other is usually called one vibration. One hesitation is followed by another. With such oscillations, a corresponding oscillation of the magnetic field occurs in the conductor.
The time spent on one oscillation is called a period and is denoted by the letter T. The period is indicated in seconds.
Frequency is one of the important quantities. It shows the number of vibrations per second and is denoted by the letter f. The name of the unit of frequency is hertz, (Hz).
Practical use
Electric direct current always always has one direction, which is called constant. It is widely applied to power electronic devices.
If the current changes direction, it is called alternating, and it is used to transfer energy through wires over long distances.
