# Is current pushed through the circuit or taken by the circuit?

I am not an electrical engineer so my concept about the practical side of ohm's law is very flimsy. What I am going to ask may sound childish but please try to explain as best as possible.

When you put let's say two things in series; an led (let's assume 150ohm) and a small 100ohm resistor, then you attach it to eight(8) 1.5v batteries, the current flowing through the circuit can be calculated by the ohms law as follows:

I = V/R = 12/250 = 0.048 amperes

A lot of internet articles say "provide" a certain current to the circuit. Does it mean that let's say if for the above circuit if you had to run 1 ampere through it, you will have to ramp up the voltage to 250?

My understanding that if the supply has no current limitation, then the current flowing through a circuit will be as per the Ohm's law. Otherwise you have to play with voltage to get a certain current flow through the circuit.

I mean can you actually force a certain current through a circuit without playing with voltage or the resistance? Could there be 2 similar voltage supplies but one with higher current than the other?

Words like "provides", "accepts", "consumes" are all just euphemisms for the circuit is on and working. It makes speaking about the circuit nicer in English.

In reality, if you have a voltage source and a load is connected to it, current will flow in the whole circuit. The magnitude of the current is dependent on the magnitude of the voltage and the magnitude of the resistance.

As you said to get more current flowing either the voltage must be increased while maintaining the same load resistance or the load resistance must be decreased while maintaining the same voltage.

• I was looking at lithium ion battery charging methodology. It talked about a "constant current- constant voltage" mechnism whereby you first keep current constant until you reach a specific voltage then you adopt constant coltage until you reach a low current when you cut off. Does "applying" current to batteries also used in the same sense or is it different? – A. Munir Apr 3 '19 at 19:43
• Same. When "applying" constant current - the voltage is varying. When applying constant voltage - the current is varying. – Eugene Sh. Apr 3 '19 at 19:48
• @A.Munir The magnitude of the current can be either positive or negative. If the charger has a higher voltage than the battery then current will flow from the charger to the battery. As the battery charges, its voltage will increase. The charger will then increase its voltage to compensate and keep the current the same. With constant voltage, it's just as it seems. The charger keeps the voltage the same and as the battery voltage increases less and less current will flow. – vini_i Apr 3 '19 at 20:04
• One other thing to note is that when a device or document instructs you to provide a current or a voltage, they almost always phrase it that way for a reason. LEDs for example, require some form of current control, the simplest form being a series resistor, due to thermal runaway. When the LED heats up, it's resistance decreases, so current will increase and with it, rate of heating. A resistor in series will increase in resistance as it heats up, and compensate. In your example, the 7.2V LED is using 0.3456W and the resistor is completely wasting 0.2304W. – K H Apr 3 '19 at 22:53
• In order to get rid of the resistor, you must provide some other form of current regulation, so even though you must regulate voltage in order to regulate current, it is better to specify the current provided, as it is the relevant data to the function of the device, and it's easier to simply say "Provide 1A" than it is to say "Vary the voltage in such a way as to cause one amp of current to flow." – K H Apr 3 '19 at 22:56

Benjamin Franklin, owner of print shops in the 1700s thus rather wealthy for that time, provided empirical tests for what became Ohms Law. When George Ohm finally had access to the steady voltage sources of the Cavendish Lab in Britain, he measured various combinations of V,I,R and happily proclaimed what we use today.

If there are 2 supplies, both providing 250 volts, one capable of 1 amp and one of 2 amps, the sole resistor being 250 ohms, then in either case only 1 amp will flow.