Just had this at school and don’t get it
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It means that if an electron were to go in the loop, it would end up at the same energy level as when it started.
Think about if this wasn’t true, you could create or destroy energy by moving electrons around in a circle!
E: If water falls 10m down and then is pumped 8m back up to the top, you would be really confused about how this is possible.
Voltage is a level. A voltage can be higher or lower than the voltage in a nearby section of the circuit. If you put the red probe of a voltmeter on point A of the circuit and the black probe on point B the meter reads 4 volts, it means that point A is 4 volts higher than point B. If you had an electron at point B, it will want to go to point A. The measure of how badly it wants to get to point A is voltage. An electron wants to flow from low voltage to high voltage. (I imagine you’re already familiar with that, but if it still troubles you, imagine a particle identical to the electron but with a positive charge. Well call it a positron. A positron wants to flow from high voltage to low voltage. The voltage is a measure of how much the positron wants to go from high voltage to low voltage).
So check out [this diagram](https://imgur.com/a/x98DZPC) if you notice, current flows through the resistor on the bottom. The voltage drop across the resistor is V=IR. I’ve labeled that voltage drop with a + and -. So this shows that blue is 2.5V higher than green. Similarly, since the bottom and top resistor are in series so the same current flows through both of them. They also have the same resistance, so they have the same voltage drop across them. That means red is 2.5V higher than green. But due to the associative property of addition, we can know that red is 5 V higher than green. This also makes sense because the 5V battery is connected from green to red.
KVL applied to the loop in this picture basically says that 2.5+2.5=5. If you get back to where you started, you must end up at the same voltage you started at. Red is at 5V. If you start at red, run to blue, to green, and back to red, it doesn’t change the fact that red is still at 5V. Starting at red, you drop 2.5V to go to blue. Then drop another 2.5V to get to green. If you want to get back to red, you have to increase by 5V. 2.5+2.5=5 it’s that simple.
The voltage rise (increase in potential across an element) and voltage drop (decrease in potential across an element) is equal within a single loop.
It is impossible for the same point in the circuit to have different voltages at the same time. KVL is just saying that you must return to where you started after completing a full loop.
Think of an odd shaped race track in the mountains. The track is a closed loop (it has no start or end). The equivalent KVL for this track is that the sum of the elevation changes around the track must be 0. If this were not so, then after one loop around the track you’d be higher or lower than where you started–which clearly doesn’t make sense.
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