Ohm's Law and Current Strength

Ohm's law is a law discovered by Ceorg Simon Ohm (1787-1854, German) in 1827. Ohm's law is the most basic calculation formula in electrical engineering. As shown in Figure 1-1, the current flowing through a circuit is proportional to the voltage across the circuit and inversely proportional to the resistance of the circuit. It can be expressed as:

Where U is the voltage across the resistor, V;
R is the resistance, Ω.

In any complete closed circuit, there are voltage, current and resistance at the same time, and their respective codes are U, I and R. The relationship between the three is: U=I×R or I=U/R and R=U/I, and can be symbolically represented by a triangle for easy memorization, as shown in Figure 1-2.

[Example 1] When a voltage of 100V is applied to the two ends of a 25l'3 resistor, what is the current flowing through the resistor?
Solution: Substitute the relevant values ​​into formula (1-1), and we get I=U/R=100/25=4(A).
[Example 2] If a current of 30mA flows through a 5kll resistor, what is the voltage applied to the two ends of the resistor?
Solution: Substitute the relevant values ​​into formula (1-1), and we get U=RI=5x103x 30X10-3=150(V).
Current intensity (current is sometimes also referred to as "current intensity") is the amount of electricity passing through the cross-section of a conductor per unit time. It can be expressed as:
I=Q/r (1-2)
[Example 3] If a current of 3A flows in a wire for 1 minute, how many electrons flow through it? It is known that the charge of an electron is -1.602x10-19C.
Solution: Assuming that the charge of an electron is e(C), the number of electrons flowing through it

[Example 4] A charge of 50C flows through a wire within 10s, what is the current in the wire?
Solution: Substituting the relevant values ​​into formula (1-2), we get I=Q/t=50/10=5(A).