Practice Questions for Science Class 10th "Magnetic Effects of Electric Current"

Multiple Choice Questions (MCQs):

1. B) Hans Christian Oersted - He discovered the magnetic effect of electric current in 1820.
2. B) Circular - The magnetic field around a straight current-carrying conductor forms concentric circles.
3. A) Right-hand thumb rule - This rule gives the direction of the magnetic field around a current-carrying conductor.
4. C) Both current and distance - The strength of the magnetic field (B) is proportional to the current (I) and inversely proportional to the distance (r) from the conductor.
5. B) A stationary charge - Only moving charges or current produce magnetic fields; stationary charges do not.
6. A) Doubles - The magnetic field strength (B) is directly proportional to the current (I), so doubling I doubles B.
7. A) Uniform - Inside a long straight solenoid, the magnetic field is nearly uniform and parallel to the axis of the solenoid.
8. C) A stronger magnetic field - More turns per unit length increase the magnetic field strength.
9. C) Form closed loops - Magnetic field lines are continuous loops; they start from the North pole, travel outside to the South pole, and return inside the magnet.
10. C) Both A and B - A current-carrying solenoid's magnetic field resembles both a bar magnet and an electromagnet.
11. A) Iron - Iron can be magnetized to form a permanent magnet due to its ferromagnetic properties.
12. C) Lorentz force - The force on a current-carrying conductor in a magnetic field is described by the Lorentz force equation.
13. A) Maximum - The force is maximum when the conductor is perpendicular to the magnetic field.
14. D) They flow from South to North - Magnetic field lines flow from North to South outside the magnet.
15. A) Attractive - Parallel currents in the same direction attract each other due to the interaction of their magnetic fields.
16. A) Tesla - The SI unit of magnetic field strength or magnetic flux density is Tesla (T).
17. D) All of the above - Increasing current, adding more turns, and using a magnetic core all increase an electromagnet's strength.
18. B) Reverse - Reversing current reverses the magnetic poles of the coil.
19. B) Maximum - The magnetic field at the center of a circular coil is at its maximum.
20. B) Galvanometer - A galvanometer uses the magnetic effect of current to deflect a magnetic needle for measuring small currents.

Short Answer Questions:

21. Right-Hand Thumb Rule: If you hold a current-carrying straight conductor with your right thumb pointing in the direction of the current, the fingers curl in the direction of the magnetic field.
22. Magnetic Field Strength and Distance: The magnetic field strength decreases inversely with the distance from the conductor (B ∝ 1/r).
23. Uniform Magnetic Field in a Solenoid: Due to the overlapping of circular magnetic fields from each turn, the field inside becomes uniform along the axis.
24. Role of Magnetic Core: It concentrates the magnetic field lines, making the electromagnet stronger by increasing magnetic permeability.
25. Reversing Current Direction: Reversing the current reverses the direction of the magnetic field around the conductor.
26. Effect on Solenoid's Length: Increasing length while keeping turns constant reduces the magnetic field strength inside the solenoid.
27. Attraction of Parallel Wires: Each wire creates a magnetic field that exerts a force on the current in the other wire, leading to attraction when currents are parallel and in the same direction.
28. Galvanometer Operation: Current through the coil produces a magnetic field that interacts with a permanent magnet, deflecting a pointer.
29. Soft vs. Hard Magnetic Materials: Soft materials (like iron) magnetize and demagnetize easily, while hard materials (like steel) retain magnetism.
30. Magnetic Field Lines: They represent the direction and strength of the magnetic field; closer lines indicate stronger fields.
31. Number of Turns and Field Strength: More turns increase the magnetic field strength as the magnetic fields from each turn add up.
32. Magnetic Moment: It's a measure of the tendency of a magnet to align with a magnetic field, influenced by current, number of turns, and area of the coil.
33. Magnetic Field Around a Circular Loop: [Sketch would show field lines looping around the loop, with the direction determined by the right-hand rule, strongest at the center.]
34. Stationary Charge: A stationary charge does not produce a magnetic field because there is no motion to create magnetic effects.
35. Turning Off an Electromagnet: Simply stop the current flow through the coil; the magnetism disappears due to the absence of current.
36. Bar Magnet vs. Electromagnet: A bar magnet is permanently magnetized, while an electromagnet's magnetism depends on an electric current and can be controlled.
37. Earth's Magnetic Field and Compass: The compass needle aligns with Earth's magnetic field, pointing towards the magnetic North.
38. Increasing Electromagnet Strength: Add more coil turns or use a core material with higher magnetic permeability without changing the current.
39. Magnetic Flux Density: Represents the strength of the magnetic field (B) through a given area, measured in Tesla.
40. Magnetic Field Away from Center of Circular Coil: It decreases as you move away from the center, following an inverse relationship with distance.

Long Answer Questions:

41. Magnetic Field Line Properties:

• They never intersect.
• They are closer together where the field is stronger.
• They form continuous loops from North to South outside the magnet.
• The tangent to any point on a line gives the field's direction.

42. Force Between Parallel Conductors:

• Each wire generates a magnetic field that interacts with the current in the other wire, causing attraction or repulsion based on current direction.

43. Magnetic Field Pattern Around a Straight Wire:

• Circular field lines around the wire, with the direction determined by the right-hand thumb rule. Reversing current reverses the field direction.

44. Soft Iron vs. Steel:

• Soft Iron: Easily magnetized and demagnetized, used in electromagnets for temporary magnetism.
• Steel: Retains magnetism better, used for permanent magnets.

45. Solenoid's Magnetic Field:

• Inside: Uniform along the axis.
• Outside: Similar to a bar magnet, with field lines looping from one end to the other.

46. Shape of Coil and Magnetic Field:

• Solenoid: Produces a nearly uniform field inside due to many overlapping circular fields.
• Circular Loop: Field is strongest at the center, decreasing radially outward.

47. Ammeter Principle:

• Uses a galvanometer with low resistance in parallel with the main circuit to measure current by deflecting a magnetic needle.

48. Factors Affecting Solenoid's Magnetic Field:

• Number of turns (N)
• Current (I)
• Length of the solenoid (L)
• Presence and nature of the core

49. Safety with Magnets:

• Keep away from electronic devices to avoid data corruption or device damage.
• Use caution to prevent strong magnets from snapping together, causing injury or damage.
• Avoid magnetic fields if you have magnetic implants or medical devices.

50. Magnetic Domains:

• Small regions within a material where magnetic moments are aligned. When domains align, the material becomes magnetized.

51. Determining Magnet Poles:

• Bring a current-carrying wire near the magnet. If the wire is attracted to one end, that's the North pole; repulsion indicates the South pole.

52. Electromagnet Applications:

• MRI machines, magnetic separation in recycling, lifting heavy objects in industry, door locks, and in scientific research.

53. Circular Coil Demonstrating Electromagnetic Force:

• Shows how a magnetic field can exert force on another current or charge, explaining why loops can attract or repel each other.

54. Biot-Savart Law:

• Provides a mathematical way to calculate the magnetic field from a current element, fundamental for understanding current-induced magnetism.

55. Bar Magnet vs. Solenoid Magnetic Field:

• Both have a North and South pole but differ in that the solenoid's field can be turned on/off and its strength adjusted.

56. Experiment with Compass Needle:

• Pass current through a wire near a compass. The needle deflects, showing the magnetic field around the wire.

57. Current Direction and Magnetic Field:

• The direction of the magnetic field reverses with current direction, as per the right-hand rule.

58. Electromagnets vs. Permanent Magnets:

• Electromagnets offer control over magnetism strength and can be switched off; permanent magnets remain constant.

59. Environmental Impact of Electromagnets:

• Energy consumption for operation, potential electromagnetic pollution, and the need for recycling or disposal of materials like copper and iron.

60. Understanding Magnetism via Solenoid:

• The behavior of magnetic field lines around a solenoid helps visualize how magnetic fields interact and how they can be directed or concentrated.

Application-Based Questions:

61. Magnetic Field Strength Calculation:

• Using B = (μ₀ * I) / (2πr), where μ₀ = 4π × 10⁻⁷ Tm/A, I = 5A, r = 0.02m; B ≈ 5 × 10⁻⁵ T

62. Increase in Magnetic Field Strength:

• Doubling the current doubles the magnetic field strength, so it increases by a factor of 2.

63. Turns to Double Field Strength:

• If B ∝ N, double the number of turns to double the field strength; so add as many turns

64. Magnetic Field Lines for Opposite Currents:

65. Force on a Wire in a Magnetic Field:

• Using F = BIL sin(θ), where B = 0.2 T, I = 3 A, F = 0.06 N, θ = 90° for maximum force, L = F / (B * I) = 0.06 / (0.2 * 3) = 0.1 m = 10 cm

66. Force Between Parallel Wires:

• Using F/L = (μ₀ * I₁ * I₂) / (2πd), where μ₀ = 4π × 10⁻⁷ Tm/A, I₁ = I₂ = 10 A, d = 0.05 m:
  • Force per length = (4π × 10⁻⁷ * 10 * 10) / (2π * 0.05) = 4 × 10⁻⁵ N/m

67. Magnetic Field at Coil's Center:

• B = (μ₀ * N * I) / (2R), where N = 100, I = 2 A, R = 0.1 m:
  • B ≈ (4π × 10⁻⁷ * 100 * 2) / (2 * 0.1) ≈ 1.26 × 10⁻³ T

68. Zero Magnetic Field Region:

• Arrange two wires carrying equal but opposite currents parallel to each other at a specific distance where the fields cancel out between them.

69. Change in Magnetic Field with Radius:

• B ∝ 1/R for a circular loop, so doubling the radius (while keeping current constant) reduces the field by half (B_new = B_original / 2).

70. Magnetizing Soft Iron:

• By passing a current through a coil (solenoid) with the iron inside, the magnetic field of the coil magnetizes the iron.

Critical Thinking Questions:

71. Designing Electrical Circuits:

• Understanding magnetic effects helps in designing circuits where magnetic fields might interfere with components or where magnetic components like inductors are used for filtering or energy storage.

72. Wiring Practices:

• Wires carrying current in the same direction should be bundled to reduce magnetic fields, while opposite currents can be used to cancel out magnetic fields, reducing electromagnetic interference.

73. Electromagnets vs. Permanent Magnets:

• Electromagnets are preferred for applications requiring variable or controllable magnetic fields, or where magnetism needs to be turned off.

74. Earth's Magnetic Field Interaction:

• Can affect compass readings, satellite navigation, and magnetic sensors. Understanding this interaction is crucial for calibration and accuracy in navigation and geophysics.

75. New Technologies from Magnetism:

• Magnetic levitation (Maglev) for transport, magnetic data storage, and developing magnetic sensors for medical diagnostics or environmental monitoring.

76. Hazards of Strong Magnetic Fields:

• Can interfere with electronic devices, pose risks to individuals with implants like pacemakers, and potentially affect biological systems. Mitigation includes shielding, distance, and time limits of exposure.

77. Magnetism and Electricity:

• They are two aspects of electromagnetism; understanding one helps in comprehending phenomena like current flow, resistance, and circuit behavior in the presence of magnetic fields.

78. Historical Significance:

• The discovery laid the foundation for electromagnetism, leading to key developments in physics, technology (like telegraphy), and modern electrical engineering.

79. Earth's Magnetic Field Changes:

• Could affect compass accuracy, satellite operations, and wildlife navigation, requiring recalibration of instruments or new technologies to maintain functionality.

80. Magnetic Field Lines as Conceptual Tools:

• They are a visual aid to understand the direction and strength of magnetic fields but do not exist physically. They help in predicting the behavior of magnets and currents but are an abstraction for complex field interactions.