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Electric Current — Revision Notes

NIOS · Class 12 · Physics

Electric Current revision notes for NIOS Class 12 Physics: 4 topics in quick points. Part of the NIOS Class 12 Physics syllabus.

45 questions35 flashcards18 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

Electric Current — Definition and Basics

  • Electric current is the rate of flow of electric charge through a cross-sectional area of a conductor.
  • Conventional current flows from higher potential to lower potential (positive to negative terminal outside the cell). Electrons actually move in the opposite direction.
  • If charge ΔQ flows in time Δt, average current I_av = ΔQ / Δt.
2

Ohm's Law, Resistance and Resistivity

  • Ohm's Law: At constant temperature and pressure, the current through a conductor is directly proportional to the potential difference across it: V = IR.
  • Resistance (R) = V/I. It opposes the flow of current. SI unit: Ohm (Ω). 1 Ω = 1 V/A.
  • Ohmic conductors: Those that obey Ohm's Law (e.g., metals). Their I-V graph is a straight line through the origin.
3

Grouping of Resistors — Series and Parallel

  • Series combination: Resistors are connected end-to-end. The SAME current flows through all resistors. Voltages add up.
  • Series equivalent resistance: R_eq = R₁ + R₂ + R₃ + ... (always GREATER than any individual resistance).
  • Parallel combination: Resistors share the same two terminal points. The SAME voltage appears across all resistors. Currents add up.
4

EMF, Internal Resistance, and Types of Cells

  • EMF (Electromotive Force) of a cell = potential difference between terminals when NO current is drawn (open circuit). It is the maximum possible voltage of the cell.
  • Internal resistance (r) is the resistance offered by the electrolyte and electrodes inside the cell to the flow of current.
  • When current I is drawn: Terminal voltage V = E - Ir (less than EMF during discharge).

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Full Notes

Key Concepts

Electric current is defined asOhm's Law (1828) states thatExperiments show that resistance ofCarbon resistors use a standard colourFor most metals

Frequently Asked Questions

What are the important topics in Electric Current for NIOS Class 12 Physics?
Key topics in Electric Current include Electric Current — Definition and Basics, Ohm's Law, Resistance and Resistivity, Grouping of Resistors — Series and Parallel, EMF, Internal Resistance, and Types of Cells. Study these first, then practise questions on each for the NIOS Class 12 board exam.
How should I revise Electric Current for the NIOS Class 12 board exam?
Learn the core ideas first, then work through the 45 practice questions on Electric Current. 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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