Ohm's law : The current flowing through the electric circuit is
directly proportional to the potential difference across the circuit and
inversely proportional to the resistance of the circuit, provide the
temperature remains constant.
Where I is the current flowing in amperes, the V is voltage applied and
R is the resistance of the conductor, as shown in the fig 1.
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| Fig. 1 Ohm's law |
The unit of potential difference is defined in such a way such the constant of proportionality is unity.
The Ohm's law can be defined as,
The ratio of potential
difference (V) between any tow points of a conductor to the current
(I) flowing between them is constant, provided that the temperature of
the conductor remains constant.
Key point :
Ohm's law can be applied either to the entire circuit or to the part of
a circuit. If it is applied to entire circuit, the voltage across the
entire circuit and resistance of the entire circuit should be taken into
account. If the Ohm's law is applied to the part of a circuit, then the
resistance of that part and potential across that part should be used.
Limitations of Ohm's law
The limitations of Ohm's law are,1) It is not applicable to the non linear devices such as diodes, zener diodes, voltage regulators etc.
2) It does not hold good for non-metallic conductors such as silicon carbide. The law for such conductors is given by,
V = K Im Where K, m are constants.
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