Physics: Resistance and Conductivity Concepts
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Questions and Answers

What happens to the resistance of a wire when its length is doubled while keeping the resistivity constant?

  • Resistance decreases by half.
  • Resistance increases by one quarter.
  • Resistance remains unchanged.
  • Resistance doubles. (correct)

    • If the original resistance of a wire is 20 ohms and its volume remains constant while its length is doubled, what effect does this have on its cross-sectional area?

  • Cross-sectional area is halved. (correct)
  • Cross-sectional area remains the same.
  • Cross-sectional area is doubled.
  • Cross-sectional area is reduced to a quarter.

    • Given a wire with initial resistance R and resistivity P, what formula is used to express resistance in terms of length and cross-sectional area?

  • R = P * (L / A) (correct)
  • R = P * (A / L)
  • R = P / (A * L)
  • R = P * (L + A)

    • What will be the new resistance if a wire of resistance 20 ohms is drawn out such that its length is increased to twice its original length while resistivity remains constant?

    <p>40 ohms (A)</p> Signup and view all the answers

    If a wire's resistivity is increased while its length and volume remain constant, what will be the effect on its resistance?

    <p>Resistance increases. (C)</p> Signup and view all the answers

    What happens to the resistance of a heater when the potential difference is increased to 120 V?

    <p>Resistance remains unchanged. (A)</p> Signup and view all the answers

    If the heater draws a current of 4A at a potential difference of 60V, what will be the relationship between current and resistance?

    <p>Current is directly proportional to potential difference. (C)</p> Signup and view all the answers

    Which of the following factors does NOT affect the resistance of a wire?

    <p>Current passing through the wire (D)</p> Signup and view all the answers

    What is the formula for calculating the area of a cross-section of a wire?

    <p>Area = $πr^2$ (C)</p> Signup and view all the answers

    When analyzing the resistivity of materials, which dimension is crucial for calculating resistance in a cylindrical wire?

    <p>Length of the wire (B)</p> Signup and view all the answers

    How does changing the diameter of the wire affect its resistance?

    <p>Resistance decreases with increased diameter. (A)</p> Signup and view all the answers

    Which component is primarily analyzed when determining the potential difference across the terminals of a circuit?

    <p>Voltage drop across each component (D)</p> Signup and view all the answers

    What does Ohm's Law state about electric current and potential difference?

    <p>Electric current is directly proportional to potential difference. (B)</p> Signup and view all the answers

    Which of the following best defines a non-ohmic conductor?

    <p>A conductor that does not have a consistent relationship between current and voltage. (D)</p> Signup and view all the answers

    What does the variable 'R' represent in Ohm's Law?

    <p>The resistance of the conductor. (C)</p> Signup and view all the answers

    If the potential difference is held constant, what happens to resistance as current increases?

    <p>Resistance decreases. (D)</p> Signup and view all the answers

    What mathematical relationship describes Ohm's Law?

    <p>$V = IR$ (A)</p> Signup and view all the answers

    Which condition must remain unchanged for Ohm's Law to hold true?

    <p>The temperature of the conductor. (C)</p> Signup and view all the answers

    What is the term for the constant of proportionality in Ohm's Law?

    <p>Resistance. (C)</p> Signup and view all the answers

    Which of the following statements about ohmic conductors is true?

    <p>They maintain a linear relationship between voltage and current. (C)</p> Signup and view all the answers

    What is the total energy consumed by the refrigerator in 30 days?

    <p>90 kWh (A)</p> Signup and view all the answers

    What is the cost of energy to operate the refrigerator for 30 days at E 45 per kWh?

    <p>E 405 (C)</p> Signup and view all the answers

    Which device is used to detect the presence of electric current in a circuit?

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

    What is the relationship between electrical resistance and power rating of lamps when in use?

    <p>Lower wattage leads to higher resistance (D)</p> Signup and view all the answers

    What unit is used to measure potential difference?

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

    What does the potential difference between two points signify?

    <p>The work done in moving a unit charge (D)</p> Signup and view all the answers

    What physical quantity remains constant when resistors are connected in series?

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

    What is the definition of electric current?

    <p>The flow of negative charges in a conductor (C)</p> Signup and view all the answers

    What should be done if the ammeter shows a pointer above the zero mark while the circuit is open?

    <p>Subtract the number of divisions from the reading (A)</p> Signup and view all the answers

    Which statement is true regarding the connection of an ammeter in a circuit?

    <p>It is connected in series to measure current (B)</p> Signup and view all the answers

    In what way does the length of a cylindrical conductor affect its resistance?

    <p>Resistance increases with length (A)</p> Signup and view all the answers

    What device is primarily used to maintain the flow of charges in an electric circuit?

    <p>An electric cell or battery (A)</p> Signup and view all the answers

    Which of the following factors does not influence the resistance of a conductor?

    <p>Voltage applied (D)</p> Signup and view all the answers

    When connecting two resistors of 52 ohms and 102 ohms, which connection yields the minimum total current?

    <p>Both in series (B)</p> Signup and view all the answers

    If a voltmeter is to be connected without affecting the circuit, what characteristic must it possess?

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

    Which property of materials are associated with resistivity?

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

    What is the primary reason metals are considered good conductors of electricity?

    <p>They contain more free electrons than insulating materials. (D)</p> Signup and view all the answers

    Which configuration of resistors would achieve a total resistance of 13.5 ohms using three 9 ohm resistors?

    <p>Two in parallel and one in series with the combination. (B)</p> Signup and view all the answers

    How does the length of a wire affect its resistance?

    <p>Resistance is directly proportional to the length. (C)</p> Signup and view all the answers

    What is Joule's law of heating as expressed mathematically?

    <p>$H = I^2Rt$ (C)</p> Signup and view all the answers

    What is the SI unit of electrical resistivity?

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

    What happens to the current drawn by bulbs rated at different power levels when connected in parallel to a 220 V supply?

    <p>The higher power bulb draws more current than the lower power bulb. (B)</p> Signup and view all the answers

    What role do alloys play in electrical heating devices compared to pure metals?

    <p>Alloys provide better heat resistance and lower melting points. (C)</p> Signup and view all the answers

    Which of the following factors does NOT affect the resistance of a conducting wire?

    <p>Color of the wire (B)</p> Signup and view all the answers

    Flashcards

    Resistance of wire

    The opposition to current flow in a wire.

    Wire length increase

    The wire's length is doubled.

    Initial resistance value

    20 ohms

    Relationship between length and resistance

    Resistance is directly proportional to the length of the wire.

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    Calculate new resistance

    To find the resistance when the length is doubled.

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    Ohm's Law

    Electric current flowing through a conductor is directly proportional to the potential difference across its ends, provided physical conditions like temperature remain unchanged.

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    Ohm's Law Formula

    V = IR, where V is voltage, I is current, and R is resistance.

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    Resistance

    The opposition to the flow of electric current.

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    Ohmic Conductor

    A conductor that obeys Ohm's Law.

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    Non-Ohmic Conductor

    A conductor that does not obey Ohm's Law.

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    Potential Difference

    The difference in electrical potential between two points in a circuit.

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    Electric Current

    The flow of electric charge.

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    Constant physical Conditions

    Temperature and other factors affecting the material, must remain consistent for Ohm's Law to apply.

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    Zero Error

    The difference between the actual zero mark and the pointer's position when the circuit is open.

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    Negative Zero Error

    When the pointer is above the zero mark, the actual reading is smaller than displayed.

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    Positive Zero Error

    When the pointer is below the zero mark, the actual reading is larger than displayed.

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    Voltmeter Connection

    A voltmeter is connected in parallel to measure the potential difference across a component.

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    Ammeter Connection

    An ammeter is connected in series to measure the current flowing through a component.

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    Resistance Factors

    The resistance of a conductor depends on its length, cross-sectional area, material, and temperature.

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    Charge Movement Condition

    Charges move in a conductor when there's a potential difference across it.

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    Device for Maintaining Potential Difference

    An electric cell or battery maintains a potential difference in a circuit.

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    What is a galvanometer?

    A galvanometer is a device that detects the presence of electric current in a circuit.

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    Which lamp offers more resistance?

    A 40 W lamp has a higher electrical resistance than a 60 W lamp when both are in use.

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    What is Volt?

    The SI unit of potential difference is Volt. It's the potential difference that moves one ampere of current through one ohm of resistance.

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    Potential difference definition.

    Potential difference between two points is the work done in moving a unit charge from one point to another.

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    What maintains potential difference?

    A source of electricity like a battery, cell, or power supply maintains a potential difference across a conductor.

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    Constant quantity in series resistors.

    Current is the same in all resistors connected in series.

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    Electric current definition.

    Electric current is the rate of flow of negative charges in a conductor.

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    Refrigerator energy consumption

    A refrigerator consumes about 90 kWh of energy in 30 days.

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    What influences resistance?

    The resistance of a wire depends on its length, cross-sectional area, and material. A longer, thinner wire made of a material with higher resistivity will have higher resistance.

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    Direct Proportionality

    When two quantities increase or decrease together at the same rate, they are directly proportional. For example, if you double the length of a wire, you double its resistance.

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    Resistivity

    A material's inherent ability to resist electrical current flow. Materials with high resistivity oppose current flow more effectively than those with low resistivity.

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    Cross-sectional area

    The area of the wire's cross-section. A larger area means more space for electrons to flow, decreasing resistance.

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    Potential difference and resistance

    Changing the potential difference across a wire does not change its resistance. Resistance is an intrinsic property of the wire.

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    Current change with voltage

    If the potential difference across a resistor is increased, the current through it will also increase proportionally.

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    Resistance Formula

    The resistance of a wire is calculated using the formula: Resistance = (Resistivity * Length) / Area

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    Series connection

    A circuit arrangement where resistors are connected end-to-end, forming a single path for current flow.

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    Parallel connection

    A circuit arrangement where resistors are connected side-by-side, providing multiple paths for current flow.

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    Joule's Law of Heating

    The heat produced by an electric current flowing through a resistor is proportional to the square of the current, the resistance, and the time for which the current flows.

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    Factors affecting resistance

    The resistance of a conductor depends on its length, cross-sectional area, material, and temperature.

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    Metals as conductors

    Metals are good conductors because they have many free electrons that can easily carry an electric current.

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    Glass as insulator

    Glass is a bad conductor because it has very few free electrons, making it difficult for current to flow.

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    Alloys in heating devices

    Alloys are preferred over pure metals in heating devices because they have low electrical conductivity and a low melting point, making them suitable for generating heat.

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    Equivalent resistance

    The total resistance of a circuit with multiple resistors, acting as a single equivalent resistor.

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    Study Notes

    Electricity Notes

    • Electric Charge: A physical property defined by excess or deficiency of electrons. A scalar quantity. SI unit: Coulomb (C). Proton charge: +1.6 x 10-19 C. Electron charge: -1.6 x 10-19 C.

    • Electric Current: The rate of flow of electric charge through a particular area. A scalar quantity. SI unit: Ampere (A). Formula: I = Q/t, where I is current, Q is charge, and t is time. Current direction is opposite to electron flow. Measured by an ammeter.

    • Electric Potential: The amount of work done to move a unit positive charge from infinity to a specific point. A scalar quantity. SI unit: Volt (V). Formula: V = W/q, where V is potential, W is work, and q is charge.

    • Electric Potential Difference: The difference in electrical potential between two points. A scalar quantity. SI unit: Volt (V). (Often called voltage). Formula: ΔV = VB - VA = WAB/q, where ΔV is potential difference, VB is potential at point B, VA is potential at point A, WAB is work done, and q is charge. Measured by a voltmeter.

    • Electric Circuit: A closed path along which electric current flows. Includes a source (like a battery or cell), a load (like a bulb or appliance), a conducting path, a switch, and fuses. Diagram uses symbols for different components.

    • Circuit Diagram: A pictorial representation of an electric circuit, using standardized symbols to show the connection of components.

    • Ohm's Law: The current through a conductor between two points is directly proportional to the voltage across the two points. Formula: V = IR, where V is voltage, I is current, and R is resistance. Applies at constant temperature.

    • Resistance: The opposition to the flow of electric current. A scalar quantity. SI unit: Ohm (Ω). Factors affecting resistance: material, length, cross-sectional area, and temperature.

    • Resistivity: A material property representing its resistance to current flow. A scalar quantity. SI unit: Ohm-meter (Ω⋅m).

    • Alloys: Mixtures of two or more metals. Often have higher resistivity than pure metals, making them suitable for heating elements.

    • Series Combination: Resistors connected end-to-end. Total resistance is the sum of individual resistances. Current is the same through all resistors, but voltage drops across each resistor.

    • Parallel Combination: Resistors connected across the same two points. Reciprocal of total resistance is the sum of reciprocals of individual resistances. Voltage is the same across all resistors, but current is divided among resistors.

    • Heating Effect of Electric Current: When current passes through a conductor, some energy is converted into heat. Joule's Law of Heating: H = I2Rt, where H is heat produced, I is current, R is resistance, and t is time.

    • Practical Applications: Heating effects are used in electric heating devices (e.g., toasters, heaters), electric bulbs, and fuses. Electrical resistance is used in circuits to limit current.

    • Power: The rate at which electrical energy is consumed or supplied. SI unit is Watt (W). Formula: P = VI = I2R = V2/R where P is power, V is voltage, I is current, and R is resistance.

    • Commercial Units: Electrical energy consumption can measured in kilowatt-hours (kWh).

    • Fuses: Safety devices that protect circuits from excessive current by melting and breaking the circuit. This prevents overheating and damage of the appliance.

    Previous Year Questions (1 Mark)

    • Galvanometer function: detects current flow.
    • Higher resistance lamp: the lower wattage lamp.
    • SI unit of potential difference: volt (V).
    • Potential difference definition: work done to move unit charge between two points.
    • Device maintaining potential difference: battery/cell/power source.
    • Physical quantity same in series: current.
    • Electric current definition: rate of flow of charge.
    • Resistance change with decreased potential difference: resistance remains constant, current halves.
    • Cross-sectional area increase resistance: resistance decreases.
    • Tungsten used for lamp filaments: high melting point and high resistivity.

    Previous Year Questions (2 Marks)

    • Alloy use in toasters: Higher resistivity, and don't oxidize as easily, preventing high temperatures.
    • Wire resistance increase by lengthening : Resistance quadruples(if length doubles, resistance quads and area halves)
    • Straight line graph in V-I graph means: proportionality between voltage and current. Method: pick two points, use the slope = ΔV/ΔI calculation.
    • Meter zero readings: use substitution method to determine zero error; calculate and subtract or add based on the position of the pointer to get the true reading.
    • Voltmeter connection: Connect in parallel. Ammeter connection: Connect in series.
    • Factors for cylindrical conductor resistance: length, area of cross-section, temperature, material.
    • Metal good conductors of electricity: higher number of free electrons to carry current. Glass has fewer free electrons, thus it's a bad conductor.
    • Alloy use for heating devices: Higher resistivity, more durable at high temperatures.

    Previous Year Questions (3 Marks)

    • Parallel resistor connection: Method to connect to get minimum/maximum current. Calculation of current.
    • Joule's law: H=I²Rt. Numerical examples (using the formula) to calculate heat.
    • Parallel resistance: Formula to calculate total resistance in a parallel configuration with three or more resistors.
    • Finding resistance: Method for connecting resistors in series or parallel to find equivalent resistance, showing connections and using the proper formulas.

    Previous Year Questions (5 Marks)

    • Deriving the heat produced by current through resistor (using Ohm's law and definition of current): Using the formula H=I²Rt.
    • Different types of connections: Explain parallel and series connections, the differences of current and voltage in both cases.
    • Specific types of connections with numerical examples: Numerical examples involving a combination of resistors in series and/or parallel.

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