Xiaobai is in class. Why can resistors limit current?

The external load r =12 ÷ 5 = 2.4 Ω. If 4A is limited by a resistor, the total resistance value is =12/4 = 3 Ω.

Power =I*IR=4*4*3=48VA=48W

The current of the resistor obtained by ohm's law is the same as that of the series circuit. The current of the resistor itself is equal to the voltage applied to the resistor divided by the resistance value, that is, I=U/R, and the current flowing through the total resistor is the current flowing through the current-limiting resistor. Power consumed on the current limiting resistor = 4 * 4 * (3-2.4) = 4 * 4 * 0.6 = = 9.6W..