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Electric Resistance and OHM's Law — Chapter Summary

ICSE · Class 12 · Physics

Summary of Electric Resistance and OHM's Law for ICSE Class 12 Physics. Part of the ICSE Class 12 Physics syllabus.

60 questions36 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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Overview

Current electricity deals with the motion of electric charge in conductors. Electric current is the rate of flow of charge, given by I = Q/t, and its instantaneous form is I = dQ/dt. In metallic conductors, current is carried by free electrons, which drift slowly under an applied electric field whil

Key Concepts

Electric current is the rate

Electric current is the rate of flow of charge: I = Q/t. One ampere means one coulomb of charge flows per second. Since one electron carries 1.6×10^-1

Current density is the current per

Current density is the current per unit cross-sectional area at a point: j = I/A. It is a vector quantity and its direction is the direction of motion

In metals

In metals, outer electrons become free electrons and move randomly with thermal speed of about 10^5 m/s. Under an electric field they acquire a small

Relaxation time is the average time

Relaxation time is the average time interval between two successive collisions of a free electron with metal ions, and it is of the order of 10^-14 s.

Ohm's law states

Ohm's law states that, for a metallic conductor kept under constant physical conditions, potential difference is directly proportional to current. Thu

Learning Objectives

  • Define electric current and current density with correct units and vector nature.
  • Explain free electrons, drift velocity, relaxation time, mean free path, and mobility.
  • State and apply Ohm's law for metallic conductors and distinguish it from the definition of resistance.
  • Relate current to drift velocity and current density in microscopic form.
  • Understand resistance, resistivity, conductivity, and conductance and their dimensional formulas.

Frequently Asked Questions

What are the important topics in Electric Resistance and OHM's Law for ICSE Class 12 Physics?
Key topics in Electric Resistance and OHM's Law include Electric Current and Current Density, Free Electrons, Relaxation Time, Drift Velocity and Mobility, Ohm's Law, Resistance and Resistivity, Derivation of Ohm's Law and Microscopic Form. Study these first, then practise questions on each for the ICSE Class 12 board exam.
How should I revise Electric Resistance and OHM's Law for the ICSE Class 12 board exam?
Learn the core ideas first, then work through the 60 practice questions on Electric Resistance and OHM's Law. 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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