Tamil Nadu Board of Secondary EducationHSC Science Class 12th
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Ohm's Law

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Ohm’s Law states that the potential difference between two points is directly proportional to the electric current.


Or V/I=R        . . .1

Or 1/I=R/V

Or I=V/R        . . .2

Or V=IR          . . .3


Where R is constant for the given conductor at a given temperature and called resistance. Resistance is the property of conductor which resists the flow of electric current through it.

SI Unit:-

SI unit of resistance is ohm. Ohm is denoted by Greek letter ‘Ω’.

R = `"V"/"I"`

If the potential difference across the two ends of a conductor is 1 V and the current through it is 1 A, then the resistance R, of the conductor is 1 Ω. That is,

1 ohm = `(1 "Volt")/ (1"Ampere")`

I = `"V"/"R"`


-It is obvious that the current through a resistor is inversely proportional to its resistance. If the resistance is doubled the current gets halved. In many practical cases it is necessary to increase or decrease the current in an electric circuit.

-A component used to regulate current without changing the voltage source is called variable resistance.

-In an electric circuit, a device called rheostat is often used to change the resistance in the circuit.


  • Ohm's law
  • Statement of Ohm's law
  • Unit of resistance
  • Conductance
  • I-V graph
  • Slope of I-V graph
  • Limitation of Ohm's law
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Shaalaa.com | Electricity part 5 (Ohms Law & resistivity)


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Electricity part 5 (Ohms Law & resistivity) [00:10:41]
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