Electricity Concepts Flashcards

Electricity

• Importance of Electricity
  • Essential in modern society.
  • Controllable and convenient energy source for homes, schools, hospitals, and industries.
• Key Questions
  • What constitutes electricity?
  • How does it flow in an electric circuit?
  • What factors regulate current in a circuit?
  • Discuss the heating effect of electric current.

11.1 Electric Current and Circuit

• Definition of Electric Current
  • Similar to air or water currents; constitutes flow of electric charge through a conductor (e.g., metallic wire).
  • Example: In a torch, batteries provide flow of charges or electric current to the bulb.
  • A switch makes a conducting link between source and load. A closed path is called an electric circuit.
  • Current flows only when the circuit is closed; if broken (open circuit), current stops.
• Expressing Electric Current
  • Current ( C) is defined as the amount of charge ( Q) passing through a cross-section of the conductor in time ( t):
    I = rac{Q}{t}
• Units of Current
  • SI Unit: Ampere (A), where 1 A = 1 C/s.
  • Subunits: milliampere (1 mA = 10^-3 A), microampere (1 µA = 10^-6 A).
  • Tool to measure current: Ammeter, connected in series.
• Example Calculation:
  • Current through a bulb:
    Given: I = 0.5 A, t = 10 min = 600 s.
    Calculation: Q = It = 0.5 imes 600 = 300 C

11.2 Electric Potential and Potential Difference

• What causes electric charge flow?
  • Analogy: Water flows in a pipe due to pressure difference. Similarly, charges flow due to potential difference in a conductor.
  • Potential Difference: Generated by batteries, sets charges in motion.
• Definition: V = rac{W}{Q}
  • Where W = work done to move a unit charge Q.
• Units of Potential Difference
  • Volt (V): 1 V = 1 J/C.
  • Measured using a voltmeter, which is connected in parallel.
• Example Calculation:
  • Work done in moving charge of 2 C across 12 V:
    W = VQ = 12 imes 2 = 24 J

11.3 Circuit Diagram

• Components:
  • Cell (battery), plug key, electrical components, connecting wires.
• Symbols for Circuit Diagram:
  • Electric Cell, Battery, Switch (open/closed), Wire Joint, etc.

11.4 Ohm’s Law

• Concept: Relationship between voltage (V) and current (I) through a conductor.
  • Observed by Georg Simon Ohm.
• Ohm's Law:
  V ext{ is proportional to } I
  or
  V = IR
• Resistance (R):
  • Proportional to length (l) and inversely proportional to area of cross-section (A).
  • Formula:
    $$ R =
    ho rac{l}{A} $$
    where  \rho is resistivity ($ ext{ in } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ }\Omega m $y).
• Example Calculations:
  • Current I from a 220 V source with R = 1200  Ω:
    I = rac{220}{1200} = 0.18 A
  • Similarly for a 100 Ω heater:
    I = rac{220}{100} = 2.2 A

11.5 Factors Affecting Resistance

• Factors:
  • Length of conductor: Longer = Higher Resistance (R ∝ l).
  • Cross-sectional area: Thicker = Lower Resistance (R ∝ 1/A).
  • Material: Different materials have different resistivities.
• Resistivity Values:
  • Conductors (e.g., Silver, Copper), Alloys (e.g., Nichrome), Insulators (e.g., Rubber, Glass).
• Example: Given R = 26 Ω, find wire resistivity and material based on diameter.

11.6 Resistance of a System of Resistors

• Series Connection:

  • Same current flows through all.
  • Total resistance:
    Rs = R1 + R2 + … + Rn

• Parallel Connection:

  • Voltage across all is same.
  • Total current:
    rac{1}{Rp} = rac{1}{R1} + rac{1}{R2} + … + rac{1}{Rn}

11.7 Heating Effect of Electric Current

• Energy Dissipation:
  • Heat produced (Joule’s law):
    H = I^2 R t
• Applications:
  • Used in electric heaters, irons, light bulbs, etc.
• Example:
  An electric iron consumes 840 W (max) at 220 V; find current and resistance.

11.8 Electric Power

• Definition: Rate of doing work:
  P = VI = I^2R = rac{V^2}{R}
• Units: Watt (W) = 1 J/s, Kilowatt (kW).
• Energy Calculation: Consumed energy = Power × Time (kWh).

Summary of Key Takeaways:

• Electric current is expressed in amperes.
• Potential difference in volts is what sets charges in motion.
• Ohm's law describes the direct relationship between voltage and current.
• Resistance is influenced by the conductor's length, area, and material.
• Heating effect of electric current is utilized in various appliances.
• Electric power is defined in terms of voltage, current, and resistance, with practical applications in energy consumption.