Current Electricity
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Questions and Answers

What is the characteristic of the resistance of thermistors with respect to temperature?

  • It remains constant with minor changes in temperature.
  • It increases with decrease in temperature.
  • It changes very slowly with temperature.
  • It changes very rapidly with change of temperature. (correct)

    • What does the resistivity of a material depend on?

  • Neither the dimensions nor the temperature of the material.
  • Only the dimensions of the material.
  • Both the dimensions and temperature of the material. (correct)
  • Only the temperature of the material.

    • What is the effect of stretching a conductor on its resistance?

  • The resistance remains constant with stretching.
  • The resistance increases due to increase in length and decrease in area. (correct)
  • The resistance increases due to increase in area and decrease in length.
  • The resistance decreases due to increase in length and decrease in area.

    • What is the unit of resistivity?

    <p>Ohm-metre (Ωm)</p> Signup and view all the answers

    What is the significance of the temperature coefficient of resistance?

    <p>It is a measure of how the resistance of a material changes with temperature.</p> Signup and view all the answers

    What is the unit of resistivity?

    <p>ohm per meter</p> Signup and view all the answers

    What is the relationship between resistance and length of a conductor?

    <p>Directly proportional</p> Signup and view all the answers

    What is the dimension of resistance?

    <p>[ML^2 T^-3 A^-2]</p> Signup and view all the answers

    What is the temperature coefficient of resistance?

    <p>Change in resistance per unit change in temperature</p> Signup and view all the answers

    What is the formula for resistivity?

    <p>R = ρl/A</p> Signup and view all the answers

    What is the term given to the property of a substance that opposes the flow of current through it?

    <p>Electrical resistance</p> Signup and view all the answers

    What is the formula for the resistance of a conductor?

    <p>R = ρl / A</p> Signup and view all the answers

    What is the S.I. unit of resistivity?

    <p>Ohm-meter (Ωm)</p> Signup and view all the answers

    What happens to the drift velocity of electrons in a conductor when its diameter is doubled?

    <p>It remains the same</p> Signup and view all the answers

    What is the term given to the change in resistance of a material with a change in temperature?

    <p>Temperature coefficient of resistance</p> Signup and view all the answers

    What happens to the equivalent emf when x cells are wrongly connected in a combination of n identical cells?

    <p>It becomes (n - 2x)E</p> Signup and view all the answers

    What is the condition for maximum power consumption by a load?

    <p>R = r</p> Signup and view all the answers

    What is the net resistance across HE in a skeleton cube made of 12 equal resistors each having resistance R?

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

    What happens to the current in a circuit when the internal resistance of the cell is zero?

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

    What is the equivalent internal resistance of n identical cells connected in series?

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

    What is the equivalent emf of a combination of n identical cells connected in series?

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

    If n identical cells are connected in parallel, what is the equivalent internal resistance of the combination?

    <p>r/n</p> Signup and view all the answers

    What is the condition for maximum power in a circuit?

    <p>R = nr</p> Signup and view all the answers

    What happens when two terminals of a cell are joined together by a thick conducting wire?

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

    What is the purpose of using a mixed grouping of cells?

    <p>To use when the internal resistance is greater than the external resistance</p> Signup and view all the answers

    What happens to the emf's of cells when they are connected in series?

    <p>They are added to each other</p> Signup and view all the answers

    What is the condition for maximum power transfer to a load?

    <p>R = r</p> Signup and view all the answers

    What is the current that flows momentarily when a cell is short-circuited?

    <p>E/r</p> Signup and view all the answers

    What is the effect of internal resistance on the emf of a cell?

    <p>It decreases the emf</p> Signup and view all the answers

    What happens to the internal resistances of cells when they are connected in parallel?

    <p>They are combined in a way that reduces the overall internal resistance</p> Signup and view all the answers

    Study Notes

    Cell Operation and Characteristics

    • The cell operates with anode and cathode; current ( i ) is defined by ( i = E - ir ).
    • The potential difference across a resistance is given by the formula ( V = iR ).
    • The potential drop inside the cell is described as ( ir ).
    • The equation for cell electromotive force (emf) is ( E = V + ir ) where ( E > V ).
    • Internal resistance of the cell is calculated using ( r = \left(\frac{E}{V} - 1\right) R ).

    Power and Current Relationships

    • Power dissipated in external resistance is represented by ( P = Vi = i^2 R = \frac{V^2}{R} ).
    • Maximum power occurs when ( P_{\text{max}} = \frac{E^2}{4r} ) and the condition ( R = r ) holds.
    • Short circuit current flows momentarily at ( i_{sc} = \frac{E}{r} ) when potential difference ( V = 0 ).

    Grouping of Cells

    • Cells can be arranged in series or parallel configurations; in series, emf’s add, while internal resistances also sum.
    • Open circuit refers to no current flowing from the cell; in this state, ( E > V ).
    • In parallel configurations, all anodes connect at one point, and all cathodes connect at another, providing the same voltage across all paths.

    Resistance and Temperature

    • Thermistors are sensitive to temperature changes; their resistances change substantially with temperature variations.
    • Resistance is influenced by several factors, including the material's temperature coefficient, length, and cross-sectional area.
    • ( R = \rho \frac{l}{A} ); where ( \rho ) is resistivity.

    Colour Coding and Resistance Measurement

    • Color bands on resistors help identify resistance values, using a standard sequence known as the color code.
    • Each color corresponds to a digit, allowing for quick calculation of resistance from labeled bands.

    Non-Ohmic Conductors

    • Non-ohmic materials such as gases and semiconductors do not follow Ohm’s law; they exhibit a dynamic resistance that changes with applied voltage.
    • Relaxation time (( \tau )) signifies the average time between collisions of charge carriers.

    Electrical Properties and Dependencies

    • Conductivity (( \sigma )), resistivity (( \rho )), and conductance (( C )) are key material properties affecting resistance.
    • The temperature coefficient (( \alpha )) indicates how resistance varies with temperature; metals typically have a positive coefficient while semiconductors may be negative.
    • The resistance-temperature relationship can be modeled as ( R_t = R_0 (1 + \alpha t) ) for temperatures below ( 300^\circ C ).
    • An established relationship for the temperature coefficient averaged over a range is given by ( \alpha = \frac{R_2 - R_1}{R_1 (t_2 - t_1)} ).

    Miscellaneous Configurations

    • Mixed grouping combines series and parallel arrangements of identical cells; equivalent emf and resistances depend on the specific configuration.
    • In practical usage, real cells experience resistance, and thus ideal conditions seldom met; designing for maximum efficiency is key.

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    Description

    Test your knowledge of resistance, conductivity, and related concepts in physics, including factors affecting resistance and units of measurement.

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