Current Electricity — A-Level Physics Revision

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What is Current Electricity?

This topic introduces the fundamental concepts of electric current, potential difference, and resistance. It covers Ohm's law as a special case for ohmic conductors and introduces the concept of resistivity, an intrinsic property of a material that determines its resistance. You will learn how factors like length, cross-sectional area, and material type affect the resistance of a conductor.

Board notes: Current, potential difference, resistance, and resistivity are fundamental concepts covered by all A-Level Physics boards (AQA, Edexcel, OCR). The experimental determination of resistivity is a common practical assessment. All boards expect an understanding of I-V characteristics for ohmic and non-ohmic components.

Worked example

Common mistakes

• 1Confusing resistance and resistivity. Resistance is a property of a specific component (R = V/I), while resistivity (ρ) is a property of the material itself. Resistance depends on the material's resistivity and its dimensions (R = ρL/A).
• 2Assuming all components obey Ohm's Law. Ohm's law (V ∝ I) only applies to ohmic conductors (like a metal wire at constant temperature). Components like semiconductor diodes and filament lamps are non-ohmic.
• 3Using incorrect units in the resistivity equation. A common mistake is forgetting to convert length to metres (m) and cross-sectional area to square metres (m²) when calculating resistivity.

Current Electricity exam questions

Exam-style questions for Current Electricity with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel and OCR specifications.

Frequently asked questions

• What is the difference between conventional current and electron flow?

  Conventional current is defined as the direction that positive charge would flow (from positive to negative). Electron flow is the actual direction that electrons move (from negative to positive). In circuit analysis, we always use conventional current.

• How does temperature affect the resistance of a metal conductor?

  For a metal conductor, resistance increases as temperature increases. This is because the positive ions in the metal lattice vibrate more, increasing the frequency of collisions with the charge-carrying electrons and impeding their flow.