Mammoth Memory

How to remember + or -

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.

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