Electricity Chapter 3 Quiz
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Questions and Answers

What is an example of a device where charges flow in a steady manner?

  • A solar panel
  • A torch (correct)
  • Lightning
  • A capacitor
  • How is electric current defined when it is steady?

  • It is the charge multiplied by time.
  • It is independent of the amount of charge.
  • It is the total voltage in the circuit.
  • It is defined as the charge divided by time. (correct)
  • What does a negative current indicate?

  • A steady current flow.
  • A backward flow of charge. (correct)
  • No flow of charge.
  • An increase in positive charge.
  • What represents the net amount of positive charge flowing in the forward direction?

    <p>q+</p> Signup and view all the answers

    Which situation best describes steady electric current?

    <p>Charges flowing continuously in one direction.</p> Signup and view all the answers

    If q is defined as the net amount of charge, how is it calculated in a steady current?

    <p>q = q+ – q–</p> Signup and view all the answers

    What is the relationship between charge q and time t for steady electric current?

    <p>q is proportional to t when current is steady.</p> Signup and view all the answers

    What is true about the flow of charges during lightning?

    <p>Charges flow in a non-steady manner.</p> Signup and view all the answers

    What happens to the resistance of a conductor if its cross-sectional area is halved?

    <p>Resistance doubles</p> Signup and view all the answers

    What is the relationship between resistance R and cross-sectional area A?

    <p>R is inversely proportional to A</p> Signup and view all the answers

    What does the constant of proportionality ρ represent in the resistance equation?

    <p>Resistivity of the material</p> Signup and view all the answers

    In the equation V = I × R, what does V stand for?

    <p>Potential difference</p> Signup and view all the answers

    What does current density j refer to in the context of conductors?

    <p>Current per unit area normal to the current</p> Signup and view all the answers

    What is the SI unit for current density?

    <p>Ampere per square meter (A/m²)</p> Signup and view all the answers

    How does the potential difference V relate to the electric field E in a conductor?

    <p>V is proportional to the length l times the electric field E</p> Signup and view all the answers

    What does the formula R = ρ(l/A) indicate about resistance?

    <p>Resistance is directly proportional to resistivity and length</p> Signup and view all the answers

    What does Ohm's law express the relationship between?

    <p>Voltage, resistance, and current</p> Signup and view all the answers

    What is the SI unit of resistance as per Ohm's law?

    <p>Ohm</p> Signup and view all the answers

    Which statement about resistance is true?

    <p>Resistance depends on both the material and dimensions of the conductor.</p> Signup and view all the answers

    If the length of a conductor is doubled while maintaining its cross-sectional area, how is the resistance affected assuming other factors remain constant?

    <p>The resistance doubles.</p> Signup and view all the answers

    For two identical conductors placed in series, how does the total potential difference across them compare to the potential difference across one conductor?

    <p>It is twice the potential difference across one conductor.</p> Signup and view all the answers

    Which equation represents the functional relationship described by Ohm's law?

    <p>$V = R I$</p> Signup and view all the answers

    What happens to the resistance if the cross-sectional area of the conductor is increased while keeping its length constant?

    <p>The resistance decreases.</p> Signup and view all the answers

    If a conductor with a resistance of R carries a current I, what is the potential difference across it according to Ohm's law?

    <p>$R imes I$</p> Signup and view all the answers

    What is the relationship between current density |j| and current I according to the equations provided?

    <p>I is equal to |j| multiplied by the cross-sectional area A.</p> Signup and view all the answers

    How is conductivity σ defined in terms of other variables according to the equations?

    <p>$ rac{ne^2}{m au}$</p> Signup and view all the answers

    According to the content, what assumption is made when deriving Ohm's law?

    <p>The charge density n and relaxation time τ are constants independent of E.</p> Signup and view all the answers

    What does the vector j represent in the context of electrical conduction?

    <p>The current density, which is parallel to the electric field E.</p> Signup and view all the answers

    What is the drift speed of conduction electrons relative to the electric field direction?

    <p>It is opposite to the direction of the electric field.</p> Signup and view all the answers

    What factors must be considered to compare the drift speed obtained in a copper wire?

    <p>Thermal speeds of copper atoms and speed of electric field propagation.</p> Signup and view all the answers

    In terms of its microstructure, what does electrical conduction primarily depend on?

    <p>The density of conduction electrons and their mean time between collisions.</p> Signup and view all the answers

    Using the information provided, what is the primary role of conduction electrons in a copper wire?

    <p>To move towards positive terminals under an electric field, generating current.</p> Signup and view all the answers

    What does 'e' represent in the given content?

    <p>Potential difference between electrodes</p> Signup and view all the answers

    What happens to the current I when the resistance R is infinite?

    <p>It becomes zero</p> Signup and view all the answers

    In the equation V = e - Ir, what does each symbol represent?

    <p>V: potential difference, e: emf, I: current, r: resistance</p> Signup and view all the answers

    Why is the term 'emf' historically used despite being a potential difference?

    <p>Due to lack of understanding at the time of its naming</p> Signup and view all the answers

    What is the effect on potential difference V when current I flows through a resistor with internal resistance r?

    <p>It decreases as I increases</p> Signup and view all the answers

    What condition is described for potential difference V when no current is flowing through the cell?

    <p>V equals e</p> Signup and view all the answers

    Which of the following statements about the cell and electrolyte is true?

    <p>Current flows from P to N through both R and the electrolyte</p> Signup and view all the answers

    What is the primary role of the internal resistance r in the equations presented?

    <p>To reflect energy loss within the circuit</p> Signup and view all the answers

    Study Notes

    Introduction to Current Electricity

    • Charges in motion create electric currents; lightning is a natural example of a charge flow.
    • Everyday devices like torches and battery-powered clocks rely on steady electric currents.

    Electric Current

    • Current is defined as the flow of electric charge over a specific area in a given time interval.
    • Positive charges (q+) and negative charges (q−) contribute differently to the net charge flow, represented as q = q+ - q−.
    • For steady currents, the current (I) is calculated as the net charge (q) divided by time interval (t): I = q/t.

    Ohm’s Law

    • Discovered by G.S. Ohm in 1828, it describes the relationship between voltage (V), current (I), and resistance (R): V = RI.
    • The unit of resistance is the ohm (Ω), which is dependent on the material and dimensions of the conductor.
    • Resistance is inversely proportional to cross-sectional area (R ∝ 1/A) and directly proportional to length (R ∝ l).
    • The resistivity (ρ) relates resistance (R) to geometry: R = ρ(l/A).

    Current Density and Electric Field

    • Current density (j) is the current per unit area, expressed as j = I/A, with SI units of A/m².
    • For a uniform electric field (E) in a conductor, the relationship with potential difference (V) is V = El.

    Mathematical Representation of Conduction

    • Drift velocity (vd) of conduction electrons in materials is calculated, and its relationship with current density can be expressed using j = (ne²/τ)E, where:
      • n = electron density
      • e = charge of an electron
      • τ = average time between collisions
      • m = mass of an electron

    Electrical Conductivity

    • Conductivity (σ) relates to charge carrier density and their mobility: σ = (ne²/τ)/m.
    • Ohm’s law holds under certain assumptions, meaning conductivity plays a critical role in current flow.

    Electromotive Force (EMF)

    • EMF (e) is the potential difference between positive and negative terminals of a cell when no current is flowing.
    • When a resistor (R) is attached, potential difference decreases due to internal resistance (r), described as V = e - Ir.

    Example Problem: Drift Speed

    • To find average drift speed of conduction electrons in a copper wire, consider:
      • Cross-sectional area: 1.0 × 10⁻⁷ m²
      • Current: 1.5 A
      • Copper density: 9.0 × 10³ kg/m³, atomic mass: 63.5 u.
    • Drift speed is opposite to the direction of the electric field, contributing to net charge flow.

    Summary

    • Critical laws and principles governing current electricity, including Ohm's Law, provide foundational knowledge for understanding electrical circuits and conduction mechanisms.
    • Electromagnetic behavior is influenced by the material properties of the conductors and their geometrical arrangements.

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    Description

    Test your knowledge on Chapter Three of electricity, focusing on current and its characteristics. This chapter covers topics like electric charges in motion and natural phenomena such as lightning. Challenge yourself with questions that delve into the fundamentals of electricity.

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