Voltage and current are like close siblings. Current flows from the place with a higher voltage to the place with a lower voltage. The generation of current must be due to the existence of voltage. However, the existence of voltage doesn't necessarily mean that current will be generated. If there is only voltage but no current, it can prove that there is an open circuit in the circuit.
Voltage is actually the potential difference, that is, the energy difference between different electric potentials. It is denoted by the symbol "U" and its unit is V (volt).
We generally connect a voltmeter in parallel across the two ends of the device being measured to measure the voltage of the device. As shown in the figure, when measuring the voltage between points A and B, it is actually the voltage applied across the lamp L1.
Current is formed because voltage drives the movement of electric charges. The free charges in a conductor perform regular directional movement under the action of the electric field force, and thus current is generated.
In a conductor, the direction of the current always follows the direction of the electric field, pointing from the place with a higher electric potential to the place with a lower electric potential.
The symbol for current is I, and its units are A (ampere) or mA (milliampere).
Comparison of voltage and current values: In a circuit, voltage is directly proportional to current. The formula is I = U/Z, where Z in the formula represents the load impedance value in the circuit.
The Formation of Electric Current
When the water pressure is very high, it can generate a large enough water flow. The smaller the water pressure is, the smaller the water flow will be.
At the end:
If there is a power source but there are no devices and circuits, no electric current will be generated. However, if there is an electric current passing through the circuits and devices, it indicates that there must be a voltage applied across the two ends of the devices and circuits.
