This article contains basic terms, the correct perception of which is the foundation for understanding the work of radio electronic devices and circuits. This article briefly outlines the concepts known to many from the school physics course, but thanks to the brevity of the material, they will not be difficult to master and memorize the beginner amateur radio.

**Voltage:**

Electrical voltage is the potential difference between the points in a circuit. The voltage itself is a force that causes a current in the circuit. Voltage can be compared to a racket hitting a tennis ball. The way the ball flies represents the flow of electric current, and your racket is nothing more than the potential force that causes it.

There are two types of voltages – direct (often supplied by a battery) and alternating (the voltage that is available in the wall outlets). Current and voltage are interdependent and must be considered together.

**Electric current:**

If a voltage source is connected to the circuit, the electrons in it will move. In order for current to flow, the circuit between the positive and negative poles of the voltage source must be closed, i.e. there must be a kind of electrical “path” between the poles of the voltage source. When the circuit is interrupted, the current stops. The basic unit of measurement of current is the Ampere.

The amount of current is determined by the number of electrons passing through a given area of the conductor in a given time. Electrons always flow from the negative pole to the positive pole. For example, a current of one ampere corresponds to about six trillion electrons per second.

**Resistance:**

A quantity that describes the resistance of a material to an electric current is called resistance, and it is measured in ohms.

**Power:**

Power is the work done per unit of time. Watt is taken as the unit of power. In electrical circuits, power is equal to the voltage on a circuit component or circuit section multiplied by the current flowing through them, P = I*U, where P is power in watts, and I is current in amperes and U is voltage in volts.

Electrical energy (power) is released in the form of heat, which first increases the temperature of the material (resistor or conductor) and then through heat transfer or radiation passes into the air or heats the surrounding objects, so a value is given which characterizes its ability to dissipate power without overheating (dissipated power).

**Capacity:**

Electrical capacitance is a value that characterizes the ability to hold an electrical charge. Total charge, i.e. the total number of electrons that can be stored in a capacitor.

Imagine two metal plates that are close together, but not touching anywhere. If you connect an electric battery to these plates, with the positive pole to one and the negative pole to the other, the electrons from the battery will flow into the plate connected to the negative pole. At the same time there will be an outflow of excess electrons from the plate connected to the positive pole of the battery. If the battery is now disconnected, there will be an excess of electrons on one plate and a lack of electrons on the other, and a potential difference will remain between them (an electrical capacitor is formed).

The basic unit of measure for capacitance is the farada (F). A farad is a very large capacitance, not achievable in electronic circuits, so we usually deal with microfarads (µF) – millionths of a farad and picofarads (pF) – millionths of a microfarad.

**Inductance:**

The flow of current through a conductor causes a magnetic field, and energy is stored in this field surrounding the conductor. The main property of inductance is that it resists changes in the flowing current.

The basic unit for measuring inductance is the genri. In practice, the units used are milligeneri (mGn) – 1/1000 genri and microgenri – 1/1000 000 genri.

**Frequency:**

Frequency is simply the number of times something happens or is repeated over a period of time. In different contexts, “frequency” can refer to different things.

For example, in the context of sound, frequency refers to the number of vibrations or oscillations of a sound wave per second. It is measured in hertz (Hz). You can think of it as the rapidity with which a sound oscillates in the air. A low frequency corresponds to low sounds and a high frequency corresponds to high sounds.

In electronics, frequency usually refers to how fast periodic changes in electrical signals occur. This is measured in hertz (Hz) and indicates how many times a signal repeats in one second.

Thus, frequency in electronics is an important parameter that determines the rate at which electrical signals repeat or change and plays a key role in the functioning of various electronic devices. For example, in computers and devices such as smartphones, processor frequency is measured in gigahertz (GHz). This indicates how many operations a processor can perform in a second. For example, a 2.5 GHz processor can perform 2.5 billion operations per second.