2
$\begingroup$

I apologize before hand if this seems too naive. I'm having a really tough time understanding the relation between voltage and current. I read that 1 Volt is the amount of work done to move a $1As$ charge (which is a finite number of electrons). So how can we have cases of voltage and current being different.

My next doubt is when we connect electrical components in series. The current remains same but voltage drops at every electrical component. But from the above doubt; how can we achieve same number of electron flow when the work done (Voltage) is being reduced. With respect to the waterfall analogy. But here as the voltage drops isn't the height of the waterfall itself being manipulated with.

$\endgroup$
1
1
$\begingroup$

You're allowed to be confused on this issue - for many students it's a new phenomenon for which no analogy is perfect.

Current is very easy to understand. As you mentioned it's basically just electrons flowing past per second. However, as it would be rather time-consuming always saying things like "the current is 1000000000000000000 electrons per second", we tend to talk about Coulombs per second, where 1 Coulomb is equivalent to $6.241\times 10^{18}$ electrons. If 1 Coulomb is flowing past every second, then we say the current is 1 Ampere.

Voltage is a little more subtle. I assume you understand the idea of gravitational potential energy - if an object is far from the earth, it has a higher gravitational potential energy than a closer object, and we can convert that potential energy into kinetic energy by dropping it. In a similar way, if you have two charged objects (say of opposite charge) then the further away they are, the more electric potential energy they have - again you can convert this electric potential energy into kinetic energy by releasing them and watching them fly towards each other.

Now in the gravitational case, the heavier your object, the more gravitational potential energy it will have (that's why falling pianos hurt more than falling hailstones) and in the Earth's gravitational field we can quantify this exactly. If an object is 1 metre off the ground then we know its gravitational potential energy is 9.81 Joules per kg.

And this quantity is analogous to the Voltage. It has units of Joules per kg, while Voltage has units of Joules per Coulomb. Just like we can talk about the gravitational potential energy per kg at a height above the earth, so we can talk about the electric potential energy per Coulomb of electrons, and we call this the Voltage.

Finally, you talked about electric components in series. It should be clear to you that the current is constant at all points: unless electrons are disappearing or building up somewhere (and we'd notice the later pretty quickly) then the flow must be constant at each point. But over time, as the electrons pass through each element of the circuit, they can lose electric potential energy, or Voltage. There's no contradiction here. With your waterfall analogy, you could just think of a multi-tiered waterfall - going through each resistor, the potential drops a little, but the overall flow remains constant.

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.