Questions & Answers

State and explain Ohm’s law.

Answer
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Hint: Ohm’s law gives the relation between current passing and voltage applied across any circuit.

Complete answer:
Ohm’s Law states that the current flowing through a conductor is directly proportional to the potential difference applied across its ends, provided the temperature and other physical conditions remain unchanged.

Current is directly proportional to voltage difference through a resistor. That is, if the current doubles, then so does the voltage. To make a current flow through a resistance there must be a voltage across that resistance. Ohm's Law shows the relationship between the voltage (V), current (I) and resistance (R).

\[\text{V}\alpha \text{I }\!\!~\!\!\text{ _or_ }\!\!~\!\!\text{ I}\alpha \text{V}\Rightarrow \text{V=IR}\]

Where R is a constant called resistance of the conductor. The value of this constant depends on the nature, length, area of cross section and temperature of the conductor.
Here,

V= potential difference in volt
I= current in ampere
R=resistance (which is a constant)

The SI unit of resistance is Ohm which is denoted by the symbol Omega \[\left( \Omega \right)\]

The necessary condition for Ohm’s law to be applicable is that temperature must be constant. The main applications of Ohm’s law are:

1. To determine the voltage, resistance or current of an electric circuit.
2. Ohm’s law is used to maintain the desired voltage drop across the electronic components.
3. Ohm’s law is also used in dc ammeter and other dc shunts to divert the current.

Note:
For ohm’s law it is a necessary condition that the temperature must be constant. It’s true only for linear electrical elements. For non-linear electrical elements with parameters like capacitance, resistance etc, the voltage and current won’t be constant with respect to time making it difficult to use Ohm’s law. Ohm’s law is not applicable for unilateral electrical elements like diodes and transistors as they allow the current to flow through in one direction only.

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