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Electric potential or potential difference?
You can compare 'potential' with height, and 'potential difference' with the difference in height. The height of an object depends upon from where you measure it. For exampl…e an object three-quarters of the way up a 1000 m mountain is +750 m from the base of the mountain, but -250 m from the top of the mountain. Note how we apply a positive or a negative sign to indicate whether we are measuring upwards or downwards. The same applies to potential. It's value depends upon from where it is measured. For example, two charged objects could have a potential of , say, +5 V with respect to earth (ground) and a potential of -15 V with respect to earth. But the potential difference between them will be +5 - (-15) = 20 V. Notice how, in the above example, we always show a positive or negative sign when we talk about potential, but we don't use these signs when we talk about a potential difference. Furthermore, it is important that we must ALWAYS specify the reference point when we describe potential -e.g. "What is the potential at point A, with respect to (say) earth?" Taking this further. It's important to know that the term 'voltage' means 'potential difference', and not 'potential'! It would be quite wrong to say that the 'voltage of an object is (say) -200 V with respect to earth'. The correct expression would be the 'potential of an object is -200 V with respect to earth'. (MORE)
