Practice Questions for Science Class 10th "Electricity"

Multiple Choice Questions (MCQs):

1. B) Ampere - Electric current is measured in amperes (A).
2. C) Volts - Potential difference is measured in volts (V).
3. C) Copper - Copper is an excellent conductor due to its low resistivity.
4. B) Doubles - According to Ohm's law (V = IR), if V doubles with R constant, I must double.
5. D) Both B and C - Ohm's law can be expressed as V = IR or I = V/R.
6. C) Both length and area of cross-section - Resistance (R) is given by R = ρL/A, where ρ is resistivity, L is length, and A is the cross-sectional area.
7. C) Ohm - Resistance is measured in ohms (Ω).
8. A) Increases - In series, resistances add up: R_total = R₁ + R₂ + ... + Rₙ.
9. D) Both B and C - Electric power can be calculated as P = I²R or P = V²/R.
10. B) Prevent overloads - Fuses melt to break the circuit when current exceeds a safe level, preventing damage.
11. A) Joule's law - The heating effect of current is given by Joule's law: H = I²Rt.
12. A) 1Ω - Parallel resistors combine with 1/R_total = 1/R₁ + 1/R₂ + 1/R₃ = 1/3 + 1/3 + 1/3 = 1, so R_total = 1Ω.
13. D) Thermometer - A thermometer does not generate electrical energy.
14. A) Positive to negative - Conventionally, current direction is from positive to negative terminal.
15. A) Conductance - Conductance is the reciprocal of resistance, measured in Siemens (S).
16. A) Increases - For most metals, resistance increases with temperature due to increased electron scattering.
17. A) 25 W - P = V²/R, original R = V²/P = 220²/100 = 484Ω. At 110V, P = (110)²/484 = 25W.
18. B) Ammeter - An ammeter measures electric current.
19. B) Low melting point - Fuse wires have a low melting point to melt and break the circuit when current is too high.
20. B) Length - Resistivity is an intrinsic property of the material and does not depend on its dimensions.

Short Answer Questions:

21. Electric Current: It is the flow of electric charge, typically measured in amperes (A). It's the amount of charge passing through a conductor per unit time.
22. Potential Difference: It's the work done per unit charge to move charge between two points, measured in volts (V). Measured using a voltmeter.
23. Ohm's Law: States that the current through a conductor between two points is directly proportional to the voltage across the two points, given constant temperature. V = IR.
24. Resistance vs. Resistivity: Resistance (R) is the opposition to current flow in a specific conductor, while resistivity (ρ) is a material property, independent of the conductor's shape, R = ρ(L/A).
25. Copper for Wires: Copper has low resistivity, good conductivity, ductility, and is cost-effective, making it ideal for electrical wiring.
26. V-I Graph Slope: The slope represents the resistance (R) of the conductor, as R = V/I. A steeper slope indicates higher resistance.
27. Series Resistors: Resistance increases as they add up (R_total = R₁ + R₂).
28. Parallel Resistors: Effective resistance decreases because 1/R_total = 1/R₁ + 1/R₂ + ..., providing multiple paths for current.
29. Electric Power: Rate at which electrical energy is transferred by an electric circuit. P = VI = I²R = V²/R.
30. Heating Effect: When current passes through a resistor, energy is converted to heat (Joule heating), H = I²Rt.
31. Fuse Function: It melts at high current to break the circuit, protecting from overload or short circuit.
32. Ammeter Role: Measures current by being connected in series with the part of the circuit where current is to be measured.
33. Electrical Energy: Work done by electric current, measured in joules (J) or watt-hours (Wh). Energy = Power x Time.
34. Earthing: Provides a path for fault current to flow safely to ground, preventing electric shocks.
35. Temperature and Resistance: Resistance usually increases with temperature in metals due to increased vibrations impeding electron flow.
36. Short Circuiting: When a low-resistance path bypasses normal circuit elements, causing a surge in current.
37. Voltmeter Function: Measures potential difference by being connected in parallel across the component of interest.
38. Tungsten Filament: Chosen for its high melting point, low evaporation rate, and ability to glow when heated by current.
39. Verifying Ohm's Law: Experimentally, vary voltage across a resistor and measure current to show V/I remains constant.
40. AC vs. DC: AC (Alternating Current) reverses direction periodically, while DC (Direct Current) flows in one direction. AC can be easily transformed for transmission.

Long Answer Questions:

41. Factors Affecting Resistance:

• Length (L): Longer wires have more resistance (R ∝ L).
• Cross-sectional Area (A): Larger area means less resistance (R ∝ 1/A).
• Material: Different materials have different resistivities (ρ).
• Temperature: For most conductors, resistance increases with temperature.

42. Series and Parallel Combinations:

• Series: Resistances add directly, increasing total resistance.
• Parallel: Resistances combine inversely, reducing total resistance, allowing more current pathways.

43. Series Resistance Formula Derivation:

• If V_total = V₁ + V₂ + V₃ and V = IR for each resistor, then
• V_total = I(R₁ + R₂ + R₃) => R_total = R₁ + R₂ + R₃.

44. Electric Heater Principle:

• Uses the Joule heating effect, where electrical energy is converted into heat through resistance. The heater's coil has high resistance to produce heat.

45. Power Consumption in Households:

• Measured in kilowatt-hours (kWh). Appliances' power ratings help calculate consumption over time. Meters measure this for billing.

46. Advantages/Disadvantages of Parallel Circuits:

• Advantages: Each appliance gets full voltage, failure doesn't affect others, easy addition of devices.
• Disadvantages: More complex wiring, potential for short circuits, higher total current from source.

47. Safety Measures:

• Fuses: Melt at high currents, breaking circuit.
• Circuit Breakers: Automatically trip to break circuit if current exceeds safe levels.
• Earthing: Prevents shocks by providing a safe path for fault currents.

48. Wire Thickness and Resistance:

• Thicker wires (larger cross-sectional area) have less resistance. Example: A wire with twice the area has half the resistance if all else is equal.

49. Electrical Conductivity:

• The ability of a material to conduct electricity, the inverse of resistivity (σ = 1/ρ). High conductivity means low resistance.

50. Length and Resistance:

• Resistance is directly proportional to length (R = ρL/A). Doubling length doubles resistance if area and material remain constant.

51. Demonstrating Heating Effect:

• Connect a filament lamp to a variable power supply, noting how brightness (heat) increases with current, per Joule's law.

52. Role of Insulators:

• Insulators like rubber or plastic prevent unintended current flow, ensuring safety and efficiency. Used in wire coatings, switch handles, etc.

53. Battery in Circuits:

• Provides voltage (potential difference) to drive current through the circuit. Its internal resistance affects the current it can supply.

54. Increasing Voltage in Circuits:

• According to Ohm's law, increasing V increases I if R remains constant, leading to more power dissipation or heat.

55. Material and Resistance:

• Materials like copper or silver have low resistivity, hence low resistance. Nichrome, used in heaters, has high resistance for heat generation.

56. Environmental Impact of Energy Generation:

• Fossil fuels emit CO₂, nuclear has waste disposal issues, renewables like solar/wind are less harmful but have land use or manufacturing impacts.

57. Work Done by Electric Current:

• Work done is the energy transferred when current flows through a potential difference. Work = Voltage × Charge (W = VQ). This energy can be converted into heat, light, or mechanical work.

58. Joule's Law of Heating:

• States that the heat produced (H) in a conductor is directly proportional to the square of the current (I²), the resistance (R) of the conductor, and the time (t) for which current flows (H = I²Rt). Applied in devices like heaters, toasters, where heat is the desired outcome.

59. Overloading in Circuits:

• Occurs when too many appliances draw current exceeding the circuit's capacity, risking overheating or fire. Prevention involves:
  • Using fuses or circuit breakers.
  • Distributing load across different circuits.
  • Not exceeding the rated capacity of outlets.

60. Effective Resistance:

• The total resistance of a combination of resistors, calculated differently for series (sum of resistances) and parallel (reciprocal sum). Effective resistance affects how current is distributed or how much voltage is dropped across different parts of a circuit.

Application-Based Questions:

61. Current through 5Ω Resistor:

• I = V/R = 10V / 5Ω = 2 A

62. Series Resistors:

• R_total = 2Ω + 3Ω + 5Ω = 10Ω

63. Current through 60W Bulb:

• P = VI => I = P/V = 60W / 240V = 0.25 A

64. Parallel Resistors:

• 1/R_total = 1/4Ω + 1/6Ω = (3+2)/12 = 5/12 => R_total = 12/5 Ω = 2.4Ω

65. Resistance of Electric Iron:

• R = V²/P = (220V)² / 1000W = 48.4 Ω

66. Potential Difference:

• V = IR = 3A × 10Ω = 30 V

67. Power Consumption:

• P = VI = 230V × 5A = 1150 W

68. Resistance of Copper Wire:

• R = ρL/A, where A = 1mm² = 1 × 10⁻⁶ m², L = 10m
• R = (1.68×10⁻⁸ Ωm × 10m) / (1×10⁻⁶ m²) = 0.168 Ω

69. Energy Consumption:

• Energy = Power × Time = 1000 W × 2 hours = 2000 Wh = 2 kWh

70. Current from 12V Battery:

• I = V/R = 12V / 4Ω = 3 A

Critical Thinking Questions:

71. Wire Heating with High Current:

• High current leads to more energy loss as heat (I²R), causing the wire to get hot, especially if the wire has significant resistance.

72. High Resistance Wires for Transmission:

• High resistance results in significant power loss due to heat (I²R), leading to inefficiency, voltage drop, and potential overheating.

73. Circuit Design and Current Distribution:

• Parallel circuits distribute current based on individual appliance resistance, allowing each to operate independently with full voltage. Series circuits share current, affecting performance.

74. Doubling Wire Length and Resistance:

• Resistance doubles because it's directly proportional to length (R = ρL/A), assuming the area and material remain constant.

75. Uninsulated Overhead Power Lines:

• Insulation would be impractical due to cost, maintenance, and weight. Air acts as an insulator, and birds sitting on one wire don't complete a circuit.

76. Material Choice and Energy Efficiency:

• Materials with lower resistivity (like copper) reduce energy loss as heat, thus improving efficiency. For heat-generating devices, high-resistance materials are chosen.

77. Superconductors in Electrical Applications:

• Superconductors offer zero resistance, potentially revolutionizing power transmission, magnetic levitation (Maglev trains), and computing with no energy loss due to resistance.

78. Challenges in Long-Distance Electricity Transmission:

• Energy loss as heat, voltage drop, and infrastructure cost. Overcome by using high-voltage transmission lines, transformers to step up/down voltage, and efficient conductors.

79. Temperature's Effect on Circuit Performance:

• Increased temperature can increase resistance in conductors, reduce efficiency, lead to thermal runaway in semiconductors, or cause thermal expansion affecting circuit components.

80. Birds on Power Lines:

• Birds don't get electrocuted because they don't provide a path to ground or another wire with a different potential. Humans touching both a wire and ground or two wires would complete a circuit through their body.