Save your life
With a normal household AC electricity of say, 120 Volts, a great deal of current can flow if the resistance is low enough. That is why if you are holding a “hot” wire with 120V relative to ground the current will flow through you to ground. If you are in insulated shoes the Resistance will be high and you will probably survive a little current flow. However, if you are well grounded, say standing in water, or holding onto a water pipe, the resistance to ground will be low and enough current may flow through you to kill you.
There is an old saying. “Voltage doesn’t kill, Current does”. That is why a bird can land on a very high voltage wire and not be hurt. The resistance from the bird to ground is infinite and thus the current is zero and the bird is fine. On the other hand if you touch a high voltage line with a metal ladder, a good low resistance conductor, you will be electrocuted.
Ordinary household batteries usually have enough internal resistance so that the current that might pass through your body will be very small.
On the other hand, if you short them out with a good conductor they can cause excessive heat and be destroyed.
Another example, consider a 12 Volt battery. As the Load’s Resistance goes down the Current through the Load will increase. So for example, if you “short out” an automobile 12 Volt Battery, meaning you make the Resistance Zero, then the Current will be the maximum the battery can deliver considering its internal resistance. This is why you can melt jumper cables if you touch them together. This is also why a spark can jump from a battery terminal to jumper cable, which can cause a fire if there is a gas built up from the battery. This is a safety issue.
In the Killinger’s Practical Electricity you will see all of these things discussed plus much much more. If you are interested in Electricity for practical purposes or just want to be better educated, this will be an excellent investment.
To learn how to work safely with electricity see Practical Electricity for Non-Electricians
