Current Electricity Basics

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Questions and Answers

What is the unit of electric current?

  • Coulomb
  • Watt
  • Volt
  • Ampere (correct)

Which of the following factors does NOT affect the electromotive force (emf) of a cell?

  • Nature of chemicals used
  • Size of the cell (correct)
  • Number of cells
  • Temperature

What does the internal resistance of a cell determine?

  • The voltage of the external circuit
  • The distance between electrodes
  • The maximum current that can be supplied by the cell (correct)
  • The amount of chemical in the cell

What is the definition of terminal potential difference?

<p>Potential difference in a circuit delivering current (D)</p> Signup and view all the answers

Which relationship correctly describes the maximum current from a cell?

<p>$I_{max} = \frac{E}{r}$ (A)</p> Signup and view all the answers

What is the effect of stronger electrolytes on the internal resistance of a cell?

<p>Decreases internal resistance (C)</p> Signup and view all the answers

Which of the following describes the relationship between internal resistance and area of electrodes?

<p>Internal resistance is inversely proportional to area (A)</p> Signup and view all the answers

Which of the following correctly defines lost volts?

<p>The potential difference across the internal resistance of a cell (D)</p> Signup and view all the answers

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Study Notes

Current Electricity Overview

  • Involves the flow of electrons or charges through a conductor.
  • Electric current ( I ) measures the rate of electric charge flow in a circuit, represented by the formula: ( I = \frac{Q}{t} ) where ( Q ) is electric charge and ( t ) is time.
  • Unit for current is the ampere (A), equivalent to ( \text{C s}^{-1} ).

Potential Difference and Electromotive Force

  • Terminal potential difference (voltage) ( V ) represents the work done in moving a unit charge across two points in a circuit.
  • Electromotive force (emf) ( E ) is the total work done per unit charge in a complete circuit: ( E = \frac{W}{Q} ) with ( W ) as work done.
  • Voltage in a circuit not delivering current, or open circuit, is also described by emf.
  • The unit of potential difference is the volt (V).

Factors Affecting Emf of a Cell

  • Depends on the quality of chemicals or materials in the cell; stronger electrolytes result in lower internal resistance and greater emf.
  • Influenced by the number of cells, time, and temperature; emf decreases with time and increasing temperature, such as in primary cells.

Internal Resistance

  • Internal resistance ( r ) is the opposition to current flow caused by the cell producing the current.
  • Determinants include:
    • Nature of chemicals or electrodes.
    • Amount and size of chemicals or electrodes.
    • Area of electrodes; internal resistance is inversely proportional to area (( r \propto \frac{1}{A} )).
    • Distance between electrodes; internal resistance is proportional to distance (( r \propto d )).
  • Higher internal resistance limits the maximum current supplied by the cell, as described by the equation: ( I_{\text{max}} = \frac{E}{r} ).

Lost Volts and External Resistance

  • Lost volt ( v ) refers to the potential difference across the internal resistance of a cell.
  • External resistance ( R ) is the opposition encountered by current in a material, affecting the overall circuit performance.

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