Summary

• Description:

  The PDF document comprises Form 3 Physics notes on the topic of Current Electricity.

  The topics and sub-topics covered in the document include:

  • Electric Potential Difference and Current
    • Electric potential difference (p.d.) is defined as the work done per unit charge in moving a charge from one point to another and is measured in volts.
    • Electric current is defined as the rate of flow of charge. The SI unit for current is the ampere (A).
    • A voltmeter measures p.d., while an ammeter measures current.
  • Ohm's Law
    • This law gives the relationship between voltage and the current flowing through a conductor.
    • Ohm's law states that the current flowing through a metallic conductor is directly proportional to the potential difference across it, provided physical conditions like temperature are kept constant.
    • The constant of proportionality is resistance (R), measured in ohms (Ω).
    • Conductors are classified as ohmic (obey Ohm's law, e.g., nichrome wire) and non-ohmic (do not obey Ohm's law, e.g., a bulb filament).
  • Resistance and Resistivity
    • Factors affecting the resistance of a metallic conductor include temperature, length of the conductor, and its cross-sectional area.
    • Resistivity (ρ) is defined as the resistance of a material of unit length and unit cross-sectional area. Its SI unit is the ohm-meter (Ωm).
    • The formula for resistivity is given as ρ = AR/l.
  • Resistors
    • Resistors are used to control the amount of current and voltage in a circuit.
    • Types of resistors include fixed resistors (wire-wound or carbon) and variable resistors (rheostats and potentiometers).
    • For resistors in series, the equivalent resistance is the sum of individual resistances: R_T = R₁ + R₂ + R₃.
    • For resistors in parallel, the reciprocal of the total resistance is the sum of the reciprocals of individual resistances: 1/R_T = 1/R₁ + 1/R₂ + 1/R₃.
  • Electromotive Force (e.m.f.) and Internal Resistance
    • Electromotive force (e.m.f.) is the potential difference across a cell when no current is being drawn from it.
    • The p.d. across the cell when the circuit is closed is called the terminal voltage.
    • Internal resistance is the opposition to the flow of current that a cell generates.
    • The relationship is given by the formula E = I(R + r) = IR + Ir = V + Ir.

  These notes are comprehensive, neat, and printable, making them an excellent resource for students studying the principles of current electricity. They are also highly suitable for teachers to use for lesson preparation, providing clear definitions, formulas, and numerous worked examples to enhance understanding.

• Length:

  12 pages
• Category:

  Lesson Notes
• Level:

  Form 3
• Subject:

  PHYSICS
• Posted By:

  Caleb_Peter

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