Current Electricity Concepts
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Questions and Answers

What is the SI unit of electric current?

Ampere

1 Ampere is equivalent to 1 Coulomb of charge flowing per second.

True (A)

Which of these are charge carriers in a metal?

  • Ions
  • Free electrons (correct)
  • Free electrons and Ions

    • What are the charge carriers in an electrolyte?

    <p>Ions (B)</p> Signup and view all the answers

    What are the charge carriers in gases?

    <p>Free electrons and Ions (A)</p> Signup and view all the answers

    What type of quantity is electric current?

    <p>Scalar (A)</p> Signup and view all the answers

    Electric current follows the vector addition rule.

    <p>False (B)</p> Signup and view all the answers

    Current Density is a vector quantity.

    <p>True (A)</p> Signup and view all the answers

    What determines the direction of current Density?

    <p>The direction of the flow of positive charge.</p> Signup and view all the answers

    Provide the formula for calculating Current Density.

    <p>J = I/A</p> Signup and view all the answers

    What is Drift Velocity?

    <p>The average velocity of free electrons with which they are attracted towards the positive end of a conductor is called drift velocity.</p> Signup and view all the answers

    Drift velocity is a scalar quantity.

    <p>False (B)</p> Signup and view all the answers

    In a conductor, what is the typical order of magnitude for drift velocity?

    <p>10^-4 m/s (A)</p> Signup and view all the answers

    What is Relaxation Time?

    <p>The time between two successive collisions of electrons is called relaxation time.</p> Signup and view all the answers

    Relaxation Time increases with increasing temperature.

    <p>False (B)</p> Signup and view all the answers

    Define Mobility.

    <p>The drift velocity obtained per unit electric field is called mobility.</p> Signup and view all the answers

    Provide the formula to calculate Mobility.

    <p>M = Vd / E</p> Signup and view all the answers

    What is Ohm's Law?

    <p>Ohm's Law states that the current flowing in a conductor is directly proportional to the potential difference applied across its ends, provided that physical conditions like temperature remain constant.</p> Signup and view all the answers

    What is the formula for Ohm's Law?

    <p>V = IR</p> Signup and view all the answers

    What is Resistance?

    <p>Resistance is the obstruction offered in the path of current due to collisions between electrons and ions.</p> Signup and view all the answers

    Define Resistivity.

    <p>Resistivity is the resistance of one unit volume of a conductor, and it is also known as specific resistance.</p> Signup and view all the answers

    What is the SI unit of Resistivity?

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

    Resistivity depends only on the material and the temperature of the substance.

    <p>True (A)</p> Signup and view all the answers

    What is the formula to calculate Resistance?

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

    What is Conductance?

    <p>Conductance is the reciprocal of resistance.</p> Signup and view all the answers

    What is the SI unit of Conductance?

    <p>Siemens (S)</p> Signup and view all the answers

    If the length of a wire is doubled, the resistance also doubles.

    <p>True (A)</p> Signup and view all the answers

    If the length of a wire is doubled by stretching it, the resistance increases four times.

    <p>True (A)</p> Signup and view all the answers

    The slope of the VI graph represents resistance.

    <p>True (A)</p> Signup and view all the answers

    In a VI graph, if the slope is greater than 90°, the resistance is negative.

    <p>True (A)</p> Signup and view all the answers

    Ohm's Law is always followed in all materials and situations.

    <p>False (B)</p> Signup and view all the answers

    What is Electromotive Force (EMF)?

    <p>The energy required by a charge to complete its cycle within a cell is called electromotive force.</p> Signup and view all the answers

    The maximum potential difference between the terminals of a cell in an open circuit is called EMF.

    <p>True (A)</p> Signup and view all the answers

    The direction of current outside the cell is from positive to negative, and inside the cell is from negative to positive.

    <p>True (A)</p> Signup and view all the answers

    Provide the formula that relates EMF, Terminal Voltage, and internal resistance

    <p>E = V + Ir</p> Signup and view all the answers

    In an open circuit, EMF is equal to terminal voltage.

    <p>True (A)</p> Signup and view all the answers

    Electromotive Force (EMF) is always greater than terminal potential difference.

    <p>False (B)</p> Signup and view all the answers

    During charging, terminal voltage is greater than EMF.

    <p>True (A)</p> Signup and view all the answers

    What is Internal Resistance?

    <p>Internal resistance is the resistance offered by the electrolyte of a cell to the flow of ions.</p> Signup and view all the answers

    Provide some factors that affect the Internal Resistance of a cell.

    <p>Factors that affect internal resistance include (1) concentration of electrolyte: Higher concentration generally leads to higher internal resistance, (2) temperature: Higher temperature typically decreases internal resistance, (3) separation between electrodes: Greater separation leads to increased internal resistance, and (4) area of the electrode: Larger electrode surface area generally leads to lower internal resistance.</p> Signup and view all the answers

    In the case of a short-circuit, the resistance R is equal to zero.

    <p>True (A)</p> Signup and view all the answers

    What is the formula to calculate current in a circuit with a short circuit?

    <p>I = E / (r + R)</p> Signup and view all the answers

    What is the formula to calculate maximum current in a short circuit?

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

    What is Kirchhoff’s Current Law?

    <p>Kirchhoff’s Current Law, also known as the Junction Rule, states that the algebraic sum of currents at a junction is always zero.</p> Signup and view all the answers

    What is Kirchhoff’s Voltage Law?

    <p>Kirchhoff’s Voltage Law, also known as the Loop Law, states that the algebraic sum of all changes in potential difference around a closed loop in a circuit is always zero.</p> Signup and view all the answers

    What is Electrical Power?

    <p>Electrical power is the rate at which electrical energy is transferred or consumed in a circuit.</p> Signup and view all the answers

    Provide three formulas for calculating Electrical Power.

    <p>P = W/T, P = VI, P = I²R</p> Signup and view all the answers

    What is the SI unit of Electrical Energy?

    <p>Joule(J)</p> Signup and view all the answers

    The commercial unit of electrical energy is the kilowatt-hour (kWh).

    <p>True (A)</p> Signup and view all the answers

    1 kWh is equal to 3.6 * 10^6 Joules.

    <p>True (A)</p> Signup and view all the answers

    In relation to electrical energy, what is Power Rating?

    <p>Power Rating refers to the power that is marked on a device for a specific voltage, and it's often referred to as rated power.</p> Signup and view all the answers

    A device may deliver different power at different voltages, but its resistance will always remain constant.

    <p>True (A)</p> Signup and view all the answers

    What is the formula to find the resistance of a device given its power rating and voltage?

    <p>R = V² / P</p> Signup and view all the answers

    Study Notes

    Current Electricity

    • Electric Current: The rate of flow of electric charge in a definite direction through any cross-section.
    • Intensity (Current): Current (I) = Charge (Q) / Time (T). SI unit: Ampere (A), where 1 A = 1 Coulomb/second.
    • Charge Carriers:
    • Metal: Free electrons
    • Electrolyte: Ions
    • Gases: Free electrons and ions
    • Current Density (J): Defined as the current flowing per unit area held normal to the flow of charge. It's a vector quantity, with direction same as direction of flow of positive charge. J = I / A, or J = I cosθ / A.
    • Drift Velocity: The average velocity of free electrons with which they are attracted towards the positive end of a conductor. Order of drift velocity in a conductor is ~10-4 m/s. The Order of Thermal Velocity is ~105 m/s.
    • Relaxation Time: The time between two successive collisions of electrons.
    • Temperature increases → Relaxation time decreases
    • Mobility: The drift velocity obtained per unit electric field, M = vd / E.
    • Ohm's Law: Current flowing in a conductor is directly proportional to the potential difference (voltage) across its ends, provided that physical conditions, like temperature, remain constant. V α I; V = IR; where R is Resistance.
    • Resistance: Obstruction offered in the path of current due to collisions between electrons and ions.
    • Resistivity (ρ): Resistance of a unit volume of a conductor. ρ = R(A/L). Units: ohm-meter (Ωm). Resistivity depends only on the material and temperature of the substance.
    • Conductance (G): Reciprocal of Resistance, G=1/R, units: siemens (S).
    • Effect of Changing Dimensions on Resistance:
    • Resistance (R) is directly proportional to length (L)
    • Resistance (R) is inversely proportional to cross-sectional area (A)
    • Slope of VI Graph: Slope of the V-I graph is equal to Resistance (R).
    • Slope of IV Graph: Slope of the I-V graph is equal to 1/Resistance (1/R).
    • Effect of temperature on Resistors:
    • Temperature increases → Resistance increases for Metals (Temperature coefficient is positive)
    • For Alloys like Constantan, Manganin, Nichrome the effect is much smaller, making them suitable for current measuring instruments and other applications
    • Temperature increases → Resistance Decreases for Semi-conductors (Temperature coefficient is negative)
    • Temperature increases → Resistance decreases for Electrolytes
    • Electromotive Force (EMF): Energy required by a charge to complete its cycle in a cell. (Not a force). The maximum potential difference between terminals of a cell in open circuit.
    • Terminal Voltage (V): Potential difference across the terminals of a cell when a current is flowing. V = E - Ir, E =emf.
    • Internal Resistance: Resistance offered to the flow of ions in the electrolyte of a cell.
    • Concentration increases → Internal resistance increases
    • Temperature increases → Internal resistance decreases
    • Separation between electrodes increases → Internal resistance increases
    • Short Circuit: When R = 0, I = E/r, Imax = E/r.
    • Series Combination of Cells: I = ne/(R+nr)
    • Parallel Combination of Cells: I = ne/(r+mR)
    • Kirchhoff's Rules:
    • Current Law (Junction Rule): Sum of currents entering a junction equals the sum of currents leaving it.
    • Voltage Law (Loop Law): Sum of voltage drops around a closed loop is zero.
    • Electric Power: The rate at which electrical energy is dissipated, P = VI = I2R = V2/R. Units: Watts (W).
    • Electrical Energy: Energy consumed, E = Pt = I2Rt = V2t/R. Units: Joules (J).
    • Power rating: The power that is marked on devices of a given voltage.
    • Heating effect: Heating = I2Rt.

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    Test your knowledge on the fundamentals of current electricity, including electric current, charge carriers, current density, and drift velocity. This quiz covers key formulas and concepts essential for understanding electric circuits. Perfect for students studying physics or related fields.

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