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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
If the potential difference across the ends of a conductor is 220 V and the resistance of the conductor is 44 Ω (ohm), then the current flowing through is _________.
- 0.2 A
- 0.5 A
- 2 A
- 5 A
Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
Write the formula of resistivity
The graph between V and I for a conductor is a straight line passing through the origin.
What should remain constant in a statement of this law?
Define ampere and volt with respect to Ohm’s law.
An ammeter placed in series with an electric radiator reads 0.5 amps and a voltmeter placed across it reads 230 volts. What is the resistance of the radiator?
Define temperature coefficient of resistance.
Which of the following I-V graph represents ohmic conductors?
A student carries out an experiment and plots the V-I graph of three samples of nichrome wire with resistances R1, R2 and R3 respectively. Which of the following is true?
The circuit depicted in the figure is employed for studying Ohm’s Law. Instead of using a standard resistor, a student opts for a glass tube filled with mercury (tube 1), connected to the circuit through two electrodes, E1 and E2. He records the readings of the ammeter and voltmeter, thereby calculating the resistance. The student repeats the experiment by substituting tube 1 with tube 2, where the same amount of mercury fills tube 2.
Neglecting internal resistance of the cell use (> or < or =) to compare:
- the resistance in both the cases.
- the voltmeter readings in both the cases.
- the specific resistance in both the cases.
