Electricity in Modern Society:

  • Electricity is essential in today’s world, used in homes, schools, hospitals, and industries.
  • It is controllable and convenient for different purposes, but how does it work? What regulates the flow? We will explore electric current, circuits, and the heating effect of electric current.

Electric Current and Circuit:

  1. Electric Current: Just like water current flows in rivers, electric current flows in conductors like metal wires. In a device like a torch, current flows from the battery through the bulb to light it up when the switch is on.
  2. Switch: A switch connects or disconnects the battery and the bulb, controlling the flow of current.
  3. Electric Circuit: A complete, closed path for electric current. If the circuit is broken (e.g., switch off), the current stops, and the bulb goes out.
  4. Current Flow: Current is the flow of charge. In metallic wires, it’s mainly the flow of electrons (negative charges). The conventional direction of current is opposite to the electron flow.
  5. Current Formula: The amount of current I is the charge Q that flows through a conductor in time t:
    • I=Q/t
  6. Units:
    • Electric charge: Coulomb (C)
    • Current: Ampere (A), where 1 A = 1 C/s.
    • Small current values are measured in milliampere (mA) or microampere (µA).
  7. Ammeter: Used to measure electric current, connected in series in a circuit.

Electric Potential and Potential Difference:

  1. Electric Potential: For current to flow, there must be a difference in electric pressure, called potential difference (like water flowing from high to low pressure).
  2. Potential Difference: This is the work done to move a charge from one point to another. V=W/Q Where V is potential difference, W is work done, and Q is charge.
  3. Units: The unit of potential difference is the volt (V).
    • 1 volt = 1 joule/coulomb (1 V = 1 J/C).
  4. Voltmeter: Used to measure potential difference, connected in parallel.

Circuit Diagram:

  • A schematic diagram helps represent electrical components using symbols. Examples include a battery, switch, and resistor.
  • Symbols for basic components:
    • Cell, Battery, Switch (open/closed), Wire joints, etc.

Ohm’s Law:

  1. Ohm’s Law: Georg Simon Ohm found that for a metallic conductor at constant temperature:
    • The potential difference (V) is directly proportional to the current (I).
    • Mathematically, V ∝ I, or V=IR, where R is the resistance of the conductor.
  2. Resistance (R): Resistance is the opposition to the flow of current. It depends on the material, length, and thickness of the conductor.
    • Resistance unit: Ohm (Ω).
  3. Current and Resistance: The current is inversely proportional to the resistance. If resistance doubles, the current is halved.
  4. Formula for Current: I=V/R​
  5. Rheostat: A variable resistor used to control the current in a circuit without changing the voltage source.

Types of Materials and Resistance:

  1. Conductors: Materials that offer little resistance to the flow of current (e.g., metals).
  2. Resistors: Materials that resist current flow more but allow some current.
  3. Insulators: Materials that offer high resistance and do not allow current flow (e.g., rubber, wood).

Applications of Electric Current:

  • The heating effect of electric current is used in electric heaters, toasters, and other devices.
  1. Factors Affecting Resistance:
    • Length: Resistance increases with the length of the conductor.
    • Area of Cross-Section: Resistance decreases as the cross-sectional area increases.
    • Material: Different materials have different resistivities. Metals and alloys have low resistivity, making them good conductors, while insulators have high resistivity.
    • Temperature: Both resistance and resistivity vary with temperature, generally increasing with higher temperatures.
  2. Ohm’s Law and Resistance:
    • Resistance (R) is directly proportional to the length (l) and inversely proportional to the cross-sectional area (A):
      • R ∝ l and R ∝ 1/A​
    • Combining these, the resistance is given by: R=ρ I/A,​ where ρ is the resistivity, a constant for each material.
  3. Resistivity:
    • Resistivity (ρ) is a material property that measures how strongly a material resists the flow of electric current. It’s measured in ohm-meters (Ω·m).
    • Low resistivity: Good conductors (e.g., copper, silver).
    • High resistivity: Insulators (e.g., rubber, glass).
  4. Resistivity Values:
    • Metals like silver, copper, and aluminum have very low resistivity, meaning they are excellent conductors of electricity.
    • Materials like rubber and glass have very high resistivity, making them good insulators.
    • Alloys like nichrome, used in heating elements, have higher resistivity compared to pure metals and are more stable at high temperatures.
  5. Temperature and Resistivity:
    • As the temperature of a conductor increases, its resistance typically increases for metals because the atoms vibrate more, obstructing the flow of electrons.
    • The resistivity of materials like alloys also increases with temperature.
  6. Example Calculations:
    • The formula R=ρ I/A​ is used to calculate resistance given the material’s resistivity, length, and cross-sectional area.
    • In problems involving resistance, the current can be calculated using Ohm’s law I = V/R​.
  7. Practical Applications:
    • Electric heating devices: Alloys with higher resistivity, such as nichrome, are used in devices like toasters and electric irons because they don’t oxidize easily at high temperatures.
    • Transmission lines: Copper and aluminum are preferred for their low resistivity.
  8. Key Concept Summary:
    • The resistance of a conductor depends on the material, length, and cross-sectional area.
    • The formula for resistance is R=ρ I/A, where ρ\rhoρ is the resistivity of the material.
  9. Resistor Combinations:
    • When resistors are connected in series, the total resistance increases. The total resistance is the sum of the individual resistances: Rtotal​​= R1 + R2+ R3… .
    • When resistors are connected in parallel, the total resistance decreases and is calculated using: 1/Rtotal​​ = 1/R1 + 1/R2+ 1/R3… .

Key Insights:

  • Increased Length: Longer wires have higher resistance.
  • Increased Cross-sectional Area: Wider wires have lower resistance.
  • Material Choice: Conductors like copper are chosen for their low resistivity, while insulators are used to prevent current leakage.
  • Temperature Effects: Resistance increases with temperature for most materials, which affects performance in circuits.

Resistors in Parallel

  • Parallel Combination: In a parallel circuit, the resistors are connected side by side. When a battery is connected to this parallel arrangement, the total current is the sum of the currents flowing through each resistor.

Key Concepts:

  1. Current Distribution:
    • In a parallel circuit, each resistor gets the same voltage. However, the current through each resistor can be different.
    • The total current, I, is the sum of the currents through each resistor.
    • This is represented as:
      • I = I1​+I2​+I3​
  2. Ohm’s Law for Parallel Circuits:
    • The current through each resistor is determined by Ohm’s law:
      •  I1​= ​V/R1​, I2​= ​V/R2​, I3​= ​V/R3​,
    • The total current can be written as:
      • I=​V/RP (where RP is the equivalent resistance).
  3. Formula for Equivalent Resistance:
    • The equivalent resistance Rp​ of resistors in parallel is calculated as:
      • 1/RP​ = 1/R1+1/R2+1/R3
    • This shows that the total resistance in a parallel circuit is always less than the smallest individual resistance.

Practical Advantages of Parallel Circuits:

  • Different Currents for Different Devices: Each device in a parallel circuit gets the same voltage but may need different currents.
  • Failure of One Device: If one resistor fails in a parallel circuit, others continue to work, unlike in series circuits where one failure affects the whole system.
  • More Efficient: Devices like electric bulbs, heaters, etc., work more efficiently when connected in parallel.

Key Formulae:

  1. Power (P):
    • P = VI = I2R = V2​/R
  2. Joule’s Law of Heating:
    The heat produced in a resistor is given by:
    • H=I2Rt
    • Heat(H) is directly proportional to the square of current, resistance, and time.

Energy Units:

  • Power (Watt): The unit of power is the watt (W), and the commercial unit of energy is kilowatt-hour (kWh).
    • 1kWh=3.6×106J.

These concepts help in solving competitive exams by understanding how resistors behave in circuits and how energy is dissipated or used in electrical devices.

THESE ALL ARE THE NOTES OF CHAPTER 11. AND AFTER SOME TIME YOU GET IMPORTANT QUESTIONS AND DIAGRAMS HERE. *#THANKS FOR VISITING, VISIT AGAIN#* 😊