Ohm's Law: U=IR(I is current and R is resistance), but this formula is only applicable to pure resistance circuits.

Series voltage, the total voltage is equal to the sum of the partial voltages, U=U 1+U2.

Characteristics of parallel voltage, branch voltage is equal to power supply voltage, U=U 1=U2.

The voltage law of series circuit: the total voltage at both ends of series circuit is equal to the sum of the voltages at both ends of each part of the circuit.

Formula: σ u = U 1+U2.

Voltage law of parallel circuit: the voltage at both ends of each branch of parallel circuit is equal, which is equal to the power supply voltage.

Formula: σ u = U 1 = U2.

Extended data

In the international system of units, the main unit of voltage is volt (V), which is denoted by the symbol V. 1 volt is equivalent to 1 joule per 1 coulomb charge, that is, 1 V = 1 J/C, and strong voltage is usually kilovolts (kV).

The transformation relationship between them is:

1kV= 1000V .

1V= 1000mV .

1mV= 1000μv .

If the magnitude and direction of the voltage do not change with time, it is called steady voltage or constant voltage, which is referred to as DC voltage for short, and is represented by the capital letter U. If the magnitude and direction of the voltage change with time, it is called transformation.

For circuit analysis, one of the most important variable voltages is sinusoidal alternating voltage (AC voltage for short), whose magnitude and direction change periodically according to sinusoidal law with time. The instantaneous value of AC voltage should be represented by lowercase letters u or u(t). The device that provides voltage in the circuit is the power supply.