Electronic – DC Voltage Polarity and Current Flow

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So I'm getting pretty familiar with Electrical Theory but one issue keeps bringing me problems. In a DC circuit, there is a negative (-) and a positive (+). I am aware that in electron flow theory, current flows from the negative (-) to positive (+). See Figure 1.
But in a car battery, the positive terminal is considered the hot lead and the negative terminal is ground. If you take a wrench and connect the negative (-) terminal to the metal chassis of the car, it won't short, but when you short the positive (+) terminal to the metal chassis, it does. See Figure 2.
My question is.. How is it possible for the positive terminal of the battery to be hot when, there is positive charge on the terminal? ? If electrons are supposed to flow from negative(-) to positive(+), wouldn't the negative terminal be considered hot and not at ground potential? Also, when the positive(+) terminal is shorted to ground, is that positively charged terminal just allowing negatively charged electrons to flow from the ground? Please Help!

schematic

simulate this circuit – Schematic created using CircuitLab

Best Answer

Electrons are flowing from negative to positive when there is a connection for them to flow. You can also think of it as "holes" (or the absence of electrons in an atom) flowing from positive to negative.

Because of historic reasons, we generally think of conventional current, or the "holes", rather than the actual electron current. You are correct that the positive terminal just "pulls negatively charged electrons."

There is also no magical node called "ground." We simply assign a point that is easy to keep track of to refer to as ground. In a circuit, you could refer to the positive terminal of the battery as ground, and simply be working with negative voltages (though it would likely cause some confusion for others interpreting your work).

Likely in the case of shorting the battery to the chassis of the car, the negative terminal of the battery is already connected to the chassis. Possibly this is done for some sort of EM shielding (vehicles are inherently very noisy environments). When you make another connection from the negative terminal of the battery to the chassis, no current flows. When you connect the positive terminal, current flows through the chassis of the vehicle to the negative terminal.