How to remember + or - (version 1)

On a battery or diagram, which is the +ve and which is the -ve end?

How do you know which end of a battery is the positive?

To remember the +ve end, first decide whether a +ve symbol ( + ) or -ve symbol ( – ) has a longer line in total:

Adding lines a and b gives you a longer total line length than just line a by itself.

As you can see the +ve needs a longer line in total, i.e. $a+b\ \mm$ .

So, in the diagram below, which is the longer line: $x\ \mm$ or $y\ \mm$ ?

Line x is bigger than line y.

Again, it's easy to see that $x\ \mm$ is the longer line.

We match the two longer lines together, i.e. the +ve with the longer line. Hence the electrical diagram is marked:

The positive end of a battery in a circuit diagram has the longer line.

Now, on a real battery, we can use the same idea.

So which is the longer line: $a+b+c+d+e\ \mm$ or $f\ \mm$ ?

Adding up the two sides of a battery.

Again, it's easy to see that $a+b+c+d+e\ \mm$ is the longer.

So we match the two longer lines together, i.e. the +ve with the longer line. Hence the battery is marked:

Positive end of a battery.