How do you define ohm's law?

Answer 1

Ohm's Law states that 'the current flowing through a conductor, at constant temperature, is directly proportional to the potential difference across that conductor'.

The ratio of voltage (U) to current (I) is called the resistance (R) of the circuit:

U/I = R

While the above equation will always determine the resistance of a circuit, Ohm's Law itself only applies to those circuits whose ratio of voltage to current remains constant over a range of voltages.

Answer 2

Ohm's law defines the relationship between current and voltage across a conductor.

It states that the voltage across two points on the conductor is proportional to the current flowing through the conductor.

Mathemetically :-

Voltage / Current = Resistance (constant).

or V / I = R.

Picking holes. The Resistance does not stay constant as the conductor heats up due to the flow of current and it changes. Practically, the change is small enough to be ignored in day to day life.

Additional Answer

Ohm's Law is not a universal law, and it only applies to certain conductors which are described as being 'linear' or 'ohmic'. Most materials and circuit components, however, are 'non-linear' or 'non-ohmic', and do not obey Ohm's Law.

For Ohm's Law to apply, the ratio of voltage to current must be constant for variations in voltage. In other words, if you were to draw a graph of changes in current as a result of changes in voltage, it must be a straight line. If the resulting graph is a curve, then Ohm's Law doesn't apply. For example, Ohm's Law doesn't apply to tungsten -so incandescent lamps do not obey Ohm's Law.

The ratio of voltage to current is, of course, resistance. So Ohm's Law is only true if the resistance of a device remains constant for variations in voltage. However, the equation R = E/I will always tell you what the resistance happens to be for any particular ratio.