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Have two different loads on two circuits, the first circuit is running at 3.3V, second is 5V. Those two loads draw exactly 100mA on each. The question is, does those two circuits have the same amount of electrons transfered in the same period of time?

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Short answer, yes. Both the circuits have same amount of electrons transferred in the same period of time.

Theory behind it:

Current is the rate of flow of charge and voltage is the amount of work done in moving that charge from some point to another point.

Now since both the circuits are drawing 100mA of current that means both the circuits have same no of electrons flowing at any particular point. But different amount of work needs to be done to achieve that same flow and hence different amount of power in both the circuits (P=VI)

A good analogy is a water, so current (rate of flow) is a flow of water where as the voltage is analogous to pressure in the system that will cause the water to flow (ie current).

So both the systems have the same amount of water flowing in given time period but one system needs to work more than the other to achieve the same rate of flow.

That means 5V circuit is putting more amount of work to maintain 100mA in circuit compared to 3.3V circuit.

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  • \$\begingroup\$ perfect explanation to clear my confusion, thank you :) \$\endgroup\$ Jul 22, 2017 at 5:36
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    \$\begingroup\$ @Mayank Why would it be more work for 5V? Isn't 5V stronger than 3.3V? It makes it looks like it needs less work because 5 volts is "stronger." \$\endgroup\$
    – johnny
    Sep 25, 2018 at 19:19
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Yes, the same number of electrons is being transferred per unit of time in each case.

Nonetheless, more power is being delivered to the load in the case with higher voltage.

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Practically, I have two situations where that amperage is the same. My Electric Vehicle charges at 16 Amps with either a 110 Volt charger or a 220 Volt charger. The 110 Volt charger takes twice the time to charge the car battery at the same amperage. When I look at my electric company's energy use in kWh the total cost to charge my car battery is approximately the same. Hence with 1/2 of the voltage, only 1/2 of the power is delivered per hour.

Back to the water analogy. Is it the case that with the 220 Volt charger, my "water flow" is the same per hour, but with the 220 Volt charger I am using "two 110 Volt hoses" (hence 2x the amount of power per hour compared to a 110 Volt charger)??

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    \$\begingroup\$ Is this an answer, or a question? You've typed it in the space reserved for answers, but you end it with a question. \$\endgroup\$
    – Hearth
    Jul 15, 2021 at 15:38

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