The relationship between resistance, current and voltage, then we should understand what Ohm's law is. In the same circuit, the current passing through a certain conductor is proportional to the voltage at both ends of the conductor and inversely proportional to the resistance of the conductor. This is Ohm's law (I=U/R). Of course, Ohm's law applies to pure resistance circuits, metal conduction and electrolyte conduction, but Ohm's law does not apply to gas conduction and semiconductor components.

Voltage

If you want to have voltage, there must be something that provides voltage. This thing is called a power supply. The direction from the positive pole of the power supply to the negative pole of the power supply is specified as the current direction. Why after connecting multiple electrical appliances (loads) to the circuit, the voltage at both ends of each load cannot reach the power supply voltage? This is because when the voltage passes through the load, work needs to be done, and voltage loss will occur if work is done.

resistance

Resistance is a unique property of the load and is related to the load itself. The resistance value is determined by the load itself. The formula of Ohm's Law only allows the resistance value to be derived when the voltage and current are known, and cannot be used to determine the resistance value. Resistance can be understood as opposing voltage and weakening the effect of voltage doing work.

Current

The value of the current is determined by the formula of Ohm's Law. Only when the voltage and resistance are determined, the current can be calculated. In other words, when at least one of the voltage and resistance changes, the current value will change. However, we cannot say that when the voltage changes, the resistance value also changes. This is because the resistance value is not affected by the formula, but only related to the load itself, so the current should be changed instead of the resistance.

Therefore, what determines the brightness of the bulb is the effect of the current doing work, which we call electric power. According to the formula, it can be known that when the voltage is constant and the current is larger, the electric power is larger, and the light bulb is brighter. Of course, due to the different load conditions in the actual circuit, there are still errors when calculating with Ohm's law. In order to be more accurate, we should use reliable instruments for actual measurement.