CBSE Physics class 12 Ohm’s Law and Resistance
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Ohm’s law: It states that “the current flowing through a conductor is directly proportional to potential difference between the ends of the conductor provided physical conditions like temperature, pressure etc. remain the same”.
or V = IR
Here V is apotential difference,I is current and R is Resistance of the conductor.
Resistance: It is the ability of a conductor to oppose the flow of electric current.
SI unit of resistance is ohm.
Factors on which resistance of a conductor depends:
- Nature of the material of the conductor
- Length of the conductor ‘l’
- Area of cross-section ‘A’
ie R ∝l
R ∝ 1/A
Where ? is resistivity of the material of the conductor.
What to study thesame topic in Hindi? click on Physics in Hindi
The resistivity of thematerial of a conductor:
If we have A=1m2 and l=1m
The resistivity of the material of a conductor is defined as the resistance of the conductor having unit length and unit area of cross section. S.I. unit is ohm-meter (Ω – m).
For the practice of Current Electricity problems & more, NCERT Physics Class 12.
Ohmic conductors: Ohmic conductors are the conductors which obey ohms law and for which V-I graph is linear.Eg: Metallic conductor.
Non-Ohmic conductors are the conductors which do not obey Ohm’s law and for which V-I graph is nonlinear.Eg:junction diodes and transistors.
Ques:Why copper is used as for making connecting wires?
Ans:BecauseCopper has low resistivity.
Ques:Why Nichrome is used as aheating element of electrical devices?
Ans: BecauseNichrome has
- i) High resistivity
- ii) High melting point.
Ques:Why aluminium wires are preferred for overhead power cables?
Ans: Aluminium has low resistivity. It is cheaper and lighter.
Ques:Ohm’s law is not a universal law. Explain.
Ans: All materials do not obey Ohm’s law. Metals obey ohms law while semiconductors, electrolytes, diodes etc. do not obey Ohm’s law. So Ohm’s law is not a universal law.
Click on Physics notes Class 12 for notes on various chapters and NCERT Solutions.
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