What is current?

What is current? In this article, you will learn the difference between current and voltage, as well as the types of current and how to measure it.

We all touch and use electricity on a daily basis. However, there are many things about electricity that you may not know. In this article, we will introduce you to the basics of current, the difference between current and voltage, types of current, and how current is measured in an easy-to-understand manner.

By reading this article you will be able to master the basics of electric current.

■ Definition of current

In electromagnetism, the amount of electricity that passes through any cross-section of a conductor per unit of time is called current strength, or current for short, and is measured in amperes (A).The larger the value of A, the greater the current passing through the circuit.

Electricity may be easier to understand if you imagine it as the flow of water in a river. The number of particles of electrons that gather and flow in 1 second is the current.

■ The difference between current and voltage

In electronic circuits, the key word that appears with the same frequency as current is voltage. The unit is the volt (V). Voltage, like current, is related to the flow of electrons in a circuit. Current is the flow of electrons, while voltage is the force that drives the flow of electrons.

The higher the voltage, the higher the current; the lower the voltage, the lower the current.

Apart from voltage, the main factor that increases current is "resistance". Think of resistance as the width of the flow of electrons. When resistance increases, the width of the electron flow decreases, resulting in a smaller current. Conversely, when resistance decreases, the width of the electron flow increases, and therefore the current flowing at one time increases.

If a higher current is required with the same resistance, this can be achieved by increasing the voltage. In general, power can be calculated as "current (A) x voltage (V)", where power is expressed as P in "watts (W)". Thus, although current and voltage are quite different, they are both important factors in the electrical world.

▪ DC and AC

There are different types of current and voltage, which can be broadly categorized as direct current (DC) and alternating current (AC). Direct current, or DC (Direct Current) for short, is a one-way flow or movement of charge, usually electrons, with the current and voltage always in the same direction.

Representative examples include dry cell batteries, batteries used in automobiles, etc., and lithium-ion batteries. In DC, the voltage is always positive (or always negative) and the current always flows in the same direction, so they may not work if installed with incorrect polarity.

Alternating current, abbreviated as "AC (Alternating Current)", refers to the periodic changes in the direction and magnitude of current and voltage over time. Its waveforms vary and have the shapes of sine, square, sawtooth and triangle waves.

Industrial power supplies, represented by household power outlets, generally utilize alternating current (AC). However, in the circuits of common electronic devices, AC is converted to DC. So now there's the question, "Why AC?"

The reason lies in the transmission of electricity. Due to the resistance of the wires, current is prone to losses during transmission, but these can be reduced by increasing the voltage. However, since it is difficult to generate high voltages from direct current, it can only be transmitted as alternating current, which is stepped down through a transformer and then supplied to electrical equipment as a power supply at industrial frequencies. The current is then usually converted to DC in the circuit of the electrical equipment.

■ Methods of measuring current

Measuring current requires a measuring instrument such as a digital multimeter. Digital multimeters vary by device, but they can measure not only current, but also voltage, resistance, and so on, allowing for a variety of measurements.

When measuring with a digital multimeter, set it to the current function before measurement. The display units include "µA", "mA" and "A", so please select the measurement range that matches the current current.

To measure current, connect the negative terminal to "COM" and the positive terminal to "A", and then connect the digital multimeter in series to the circuit.

As a precaution, do not apply a voltage to the current function. Failure to do so will cause an overcurrent to flow through the measuring instrument and burn out the circuitry. The measuring instrument is actually equipped with a fuse protection circuit, but be aware that this may also be the cause of malfunction. To prevent danger, some digital multimeters do not have a current input terminal.

■ Measuring current with a digital multimeter

As the name suggests, current is the flow of charge in an electronic circuit, and the greater the flow, the greater the current value. Although current and voltage are different, both are important factors in circuits and should be understood in relation to each other.

You can measure current using a digital multimeter. When measuring current, you can refer to the information provided in this article.