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Ohm’s Law

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Ohm’s law defines the relationships between current, voltage and resistance.
A good way to understand ohm’s law is an analogy with a domestic water system. The same way that an electric current flows through a copper wire, water flows through a copper pipe in a water system. Most people do not think to much about the fact but when they turn on tap the water comes out as a result of the pressure that is provided  by a pumping station some miles away. This water pressure is similar to that used to drive electricity around a circuit, the potential difference or pd for short is the term that is used.


1 Ohm
Can be defined as the amount of resistance that will produce a potential difference (p.d.) or voltage of 1 Volt across it when a current of 1 Ampere flowing through it.

1 Ampere
Can be defined as the amount of current which, when flowing through a resistance of 1 Ohm will produce a potential difference of 1 Volt across the resistance.

1 Volt
Can be defined as the difference in potential (voltage) produced across a resistance of 1 Ohm through which a current of 1 Ampere is flowing.

“When the temperature is constant, the potential difference across the ends of a resistance is proportional to the current flowing through it”


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9 years ago

One of the easiest formulas to understand and one that can point to many problems in old radio and TV sets.


5 years ago

A useful way for beginners to remember Ohms Law;

If you use E instead of V (E = Electromotive Force) and put the three letters in a triangle, ignore the one you want to find and the other two letters give you the formula.

If combined with the formula for power – W = EI – you can get additional useful formulae to use when you know the resistance but only one of the other values, thus:

W = — and W = i²R

The commonest mistake that is made with Ohm’s law is the “When the temperature is constant” bit. Ignore it at your peril!

5 years ago

‘put the three letters in a triangle’ shoulf have read: put the three letters in a triangle in alphabetical order.

That’s the reason for using E for voltage!

5 years ago

I used the triangle but I was OK with V for voltage, the V/IR just worked for me but yes I can see the merits of E/IR with it being in alphabetical order.


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