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प्रश्न
Obtain the macroscopic form of Ohm’s law from its microscopic form and discuss its limitation.
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उत्तर
- Consider a segment of wire of length l and area of cross-section A
- Electric field is created when a potential difference V is applied
- If ‘E’ is uniform, then, V = El
- Current density, J = σ E = σ`"V"/l`
Since J = `"I"/"A"`
`"I"/"A" = sigma "V"/l`
Rearranging the above equation, Current through the conductor
Current through the conductor
V = `"I"(l/(sigma"A"))`
Where `(l/(sigma"A"))` → resistance of conductor (R)
∴ R `alpha (l/(sigma"A"))`
∴ The macroscopic form of Ohm's law is
V = IR ...[V α I]
Limitations:
There are certain materials and devices where the proportionality of V and I does not hold good.
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संबंधित प्रश्न
Graph showing the variation of current versus voltage for a material Ga As is shown in the figure. Identify the region of
(i) negative resistance
(ii) where Ohm's law is obeyed.
The relationship between the potential difference and the current in a conductor is stated in the form of a law.
1) Name the law.
2) What does the slope of V-I graph for a conductor represent?
3) Name the material used for making the connecting wire.
Fill in the following blank with suitable words:
Resistance is measured in .............. The resistance of a wire increases as the length ..............; as the temperature ..............; and as the cross-sectional area .............. .
The resistors R1, R2, R3 and R4 in the figure given below are all equal in value.
What would you expect the voltmeter A, B and C to read assuming that the connecting wires in the circuit have negligible resistance?
- Draw a V-I graph for a conductor obeying Ohm’s law.
- What does the slope of V–I graph for a conductor represent?
What are non-ohmic conductors? Give one exmaple. Draw a current-voltage graph for a non-ohmic conductor.
The slope of voltage (V) versus current (I) is called:
The temperature of a conductor is increased. The graph best showing the variation of its resistance is:
State Ohm’s law? How can it be verified experimentally? Does it hold good under all conditions? Comment.
A metal rod of length 10 cm and a rectangular cross-section of 1 cm × `1/2` cm is connected to a battery across opposite faces. The resistance will be ______.
