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Current Electricity — Revision Notes

Jammu & Kashmir Board · Class 12 · Physics

Current Electricity revision notes for Jammu & Kashmir Board Class 12 Physics: 4 topics in quick points. Includes Electric Current and Current Density.

87 questions56 flashcards17 formulas & key relations5 concepts

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Graphs showing the variation of resistivity with temperature for different types of materials: metals, semiconductors, and alloys.
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Key Topics to Revise

1

1. Electric Current and Current Density

  • Electric current is the net charge crossing a cross-section per unit time.
  • For steady current, current is defined by I = q/t.
  • For non-steady current, current at time t is given by I(t) = lim_{Δt→0} ΔQ/Δt.
2

2. Ohm's Law, Resistance, Resistivity, and Conductivity

  • Ohm discovered the law in 1828 before the microscopic mechanism of current flow was understood.
  • Ohm's law states that V = RI for many conductors under suitable conditions.
  • The SI unit of resistance is ohm, symbol Ω.
3

3. Microscopic Origin of Resistance: Drift Velocity, Relaxation Time, and Mobility

  • Without an electric field, electrons move randomly and the average velocity is zero.
  • With an electric field, electrons acquire a small average drift velocity opposite to the field.
  • The average time between successive collisions is called relaxation time τ.
4

4. Limits of Ohm's Law and Materials Classification

  • Not all materials obey a linear V-I relation.
  • Three deviations are important: non-linear V-I relation, dependence on sign of V, and non-unique V-I relation.
  • A diode is an example where the V-I relation depends on the sign of V.

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Full Notes

Key Concepts

Current is the net charge passingCurrent is a scalar quantityFor a uniform conductorOhm's law states V = RIIn an electric field

Frequently Asked Questions

What are the important topics in Current Electricity for Jammu & Kashmir Board Class 12 Physics?
Key topics in Current Electricity include Electric Current and Current Density, Ohm's Law, Resistance, Resistivity, and Conductivity, Microscopic Origin of Resistance: Drift Velocity, Relaxation Time, and Mobility, Limits of Ohm's Law and Materials Classification. Study these first, then practise questions on each for the Jammu & Kashmir Board Class 12 board exam.
How should I revise Current Electricity for the Jammu & Kashmir Board Class 12 board exam?
Learn the core ideas first, then work through the 87 practice questions on Current Electricity. Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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All Jammu & Kashmir Board Class 12 Physics Revision Notes

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