Batteries are sources of Direct Voltage meaning the pressure it provides moves the electrons in a constant current in one direction, like the flow of water down a river.
Direct voltage is usually represented with a capital V with some dots above it and a small horizontal line. If we plotted this voltage against time, it would produce a straight line.
The voltage in our wall sockets is alternating voltage, this is a different type of electricity, in this type the electrons alternate between flowing forwards and backwards because the polarity of the circuit is changing like the tide of the sea, if we plotted this voltage against time, we get a sine wave as it moves forward and rises to its maximum and then starts to decline, it passes through the zero and then the current is flowing backwards but it hits its minimum and then reverses direction again.
This is usually represented with a capital V with a wave line above it.
The voltage at wall sockets varies depending on where in the world we are. The majority of the world uses 220-240V but North, central and some of south America as well as a few other countries scattered across the planet will use 100-127V.
We can measure the voltage at our sockets and see that it actually changes slightly throughout the day, by using a cheap energy meter.
The reason for the different voltages around the world goes all the way back to the beginning when electricity first started being distributed, there was no standardisation so each distribution network had it’s own voltage and frequency for whatever their engineers felt was best. Eventually over time some companies grew and dominated the market and so voltage and frequency standardised as their products and services expanded, governments also stepped in and passed laws so that people could buy products easily and also trade products with other countries.
This is still a problem to this day, for example if we take a hair drier from the US, rated at 110V and plug it into a wall socket in Europe which has 220V. The hair drier will burn out at full power because there is too much voltage or too much pressure and the device can’t cope.
If we took a hair drier from Europe and plugged it into a US socket, it probably won’t turn on and if it does it’s going to be very weak because there isn’t enough pressure for it to function.
Some products can be used in different voltages. You need to check the manufacturers lables on the product to first see if the product has been designed to cope with different voltages.
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