1. The vertical component of earth's magnetic field is zero at or The earth's magnetic field always has a vertical component except at the
Correct Answer: (d) Magnetic equator
The vertical component of Earth's magnetic field is zero at the magnetic equator. At the magnetic poles, the field is entirely vertical, while at the magnetic equator, it's entirely horizontal.
2. The region where the Earth's magnetic field is most similar to that of a perfect dipole is called:
Correct Answer: (a) Magnetosphere
The magnetosphere is the region around Earth where the magnetic field behaves most like a perfect dipole. Further out, the solar wind distorts the field lines.
3. A dip circle is at right angle to the magnetic meridian. What will be the apparent dip?
Correct Answer: (d) 90°
When the dip circle is perpendicular to the magnetic meridian, it measures the apparent dip. The apparent dip (δ') is related to the true dip (δ) by: cot²δ' = cot²δ + 1. When the dip circle is at right angles to the magnetic meridian, the apparent dip becomes 90°.
4. Intensity of magnetic field due to earth at a point inside a hollow steel box is
Correct Answer: (d) Zero
A hollow steel box acts as a magnetic shield due to its high permeability. The magnetic field lines prefer to pass through the steel rather than the hollow interior, making the field inside effectively zero.
5. A dip needle in a plane perpendicular to magnetic meridian will remain
Correct Answer: (b) Horizontal
In a plane perpendicular to the magnetic meridian, the dip needle experiences only the horizontal component of Earth's magnetic field, causing it to remain horizontal.
6. At a certain place, the horizontal component of earth's magnetic field is √3 times the vertical component. The angle of dip at that place is
Correct Answer: (a) 30°
The angle of dip (θ) is related to the horizontal (H) and vertical (V) components by: tanθ = V/H. Given H = √3 V, so tanθ = V/(√3 V) = 1/√3 ⇒ θ = 30°.
7. The phenomenon of secular variation in Earth's magnetic field refers to:
Correct Answer: (c) Long-term changes over centuries
Secular variation refers to slow changes in Earth's magnetic field that occur over time scales of years to centuries, including changes in declination, inclination, and intensity.
8. The angle between the magnetic meridian and geographical meridian is called
Correct Answer: (b) Angle of declination
The angle of declination is the angle between true north (geographic north) and magnetic north (direction a compass points). It varies by location and changes over time.
9. At a place, if the earth's horizontal and vertical components of magnetic fields are equal, then the angle of dip will be
Correct Answer: (b) 45°
The angle of dip (θ) is given by tanθ = V/H. When V = H, tanθ = 1 ⇒ θ = 45°.
10. Earth's magnetic field always has a horizontal component except at or Horizontal component of earth's magnetic field remains zero at
Correct Answer: (b) Magnetic poles
At the magnetic poles, the Earth's magnetic field is entirely vertical, so the horizontal component is zero. At the magnetic equator, the field is entirely horizontal.
11. The dynamo theory explains the origin of Earth's magnetic field as being caused by:
Correct Answer: (c) Convection currents in the liquid outer core
The dynamo theory proposes that Earth's magnetic field is generated by the motion of electrically conducting molten iron in the outer core, which creates electric currents that produce the magnetic field.
12. The angle of dip at a place is 40.6° and the intensity of the vertical component of the earth's magnetic field is 0.5 Tesla. The total intensity of the earth's magnetic field (I) at this place is
Correct Answer: (b) 0.77 T
The vertical component V = I sinθ ⇒ I = V/sinθ = 0.5/sin(40.6°) = 0.5/0.651 ≈ 0.77 Tesla
13. The South Atlantic Anomaly is characterized by:
Correct Answer: (b) A region where the inner Van Allen belt comes closest to Earth's surface
The South Atlantic Anomaly is a region where Earth's magnetic field is weakest, allowing the inner Van Allen radiation belt to come closer to the surface, posing radiation hazards to satellites and spacecraft.
14. At a certain place the angle of dip is 30° and the horizontal component of earth's magnetic field is 0.50 Oersted. The earth's total magnetic field is
Correct Answer: (c) 0.58 Oe
H = I cosθ ⇒ I = H/cosθ = 0.50/cos(30°) = 0.50/0.866 ≈ 0.58 Oersted
15. Paleomagnetism provides evidence for:
Correct Answer: (b) Continental drift and plate tectonics
Paleomagnetism studies the record of Earth's magnetic field in rocks. The alternating magnetic orientations in seafloor rocks provided crucial evidence for seafloor spreading and plate tectonics.
16. The lines of forces due to earth's horizontal component of magnetic field are
Correct Answer: (a) Parallel straight lines
The horizontal component of Earth's magnetic field is uniform over small areas, so its field lines are parallel straight lines pointing towards magnetic north.
17. The angle of dip at a place is 60°. At this place the total intensity of earth's magnetic field is 0.64 units. The horizontal intensity of earth's magnetic field at this place is
Correct Answer: (d) 0.32 units
H = I cosθ = 0.64 × cos(60°) = 0.64 × 0.5 = 0.32 units
18. The angle of dip at the magnetic equator is
Correct Answer: (a) 0°
At the magnetic equator, the Earth's magnetic field is entirely horizontal (parallel to the surface), so the angle of dip (the angle the field makes with the horizontal) is 0°.
19. The Gauss coefficients in spherical harmonic analysis of Earth's magnetic field represent:
Correct Answer: (b) The strength of different spatial wavelengths in the field
The Gauss coefficients quantify the contributions of different spherical harmonic components to Earth's magnetic field, with lower degree terms representing larger-scale features.
20. The angle between the earth's magnetic and the earth's geographical axes is
Correct Answer: (d) None of these
The angle between Earth's magnetic and geographic axes varies but is currently about 11°. This angle changes over time due to the movement of the magnetic poles.
21. A bar magnet is placed north-south with its north pole due north. The points of zero magnetic field will be in which direction from the centre of the magnet
Correct Answer: (b) East and west
The neutral points (where Earth's field cancels the magnet's field) will be along the equatorial line of the magnet, which is east and west when the magnet is aligned north-south.
22. The lines joining the places of the same horizontal intensity are known as
Correct Answer: (e) Isodynamic lines
Isodynamic lines connect points of equal magnetic field intensity. Isogonic lines connect points of equal declination, isoclinic lines connect points of equal dip, and agonic lines connect points of zero declination.
23. The magnetic susceptibility of a material that would be most effective in shielding against Earth's magnetic field is:
Correct Answer: (c) Strongly positive (ferromagnetic)
Ferromagnetic materials with high magnetic permeability (like mu-metal) are most effective for magnetic shielding as they provide a preferred path for magnetic flux lines, diverting them away from the shielded volume.
24. At which place, earth's magnetism become horizontal
Correct Answer: (d) Magnetic equator
At the magnetic equator, Earth's magnetic field is entirely horizontal (parallel to the surface). At the magnetic poles, it's entirely vertical.
25. The Curie temperature is significant in geomagnetism because:
Correct Answer: (a) It marks the depth where core materials lose their ferromagnetism
The Curie temperature is the point above which ferromagnetic materials lose their permanent magnetic properties. In Earth's crust, this determines how deep rocks can retain their magnetization.
26. A line passing through places having zero value of magnetic dip is called
Correct Answer: (d) Aclinic line
An aclinic line connects points where the magnetic dip (inclination) is zero (i.e., at the magnetic equator). Isoclinic lines connect points of equal dip, isogonic lines connect points of equal declination, and agonic lines connect points of zero declination.
27. The magnetic field of earth is due to
Correct Answer: (a) Motion and distribution of some material in and outside the earth
Earth's magnetic field is primarily generated by the dynamo effect - the motion of electrically conducting molten iron in the outer core. Smaller contributions come from magnetized rocks in the crust and electric currents in the ionosphere and magnetosphere.
28. A very small magnet is placed in the magnetic meridian with its south pole pointing north. The null point is obtained 20 cm away from the centre of the magnet. If the earth's magnetic field (horizontal component) at this point be 0.3 gauss, the magnetic moment of the magnet is
Correct Answer: (b) 2.4 × 10⁻⁴ A·m²
At the null point, the magnet's field equals Earth's field: (μ₀/4π)(2M/r³) = Bₑ
M = (Bₑ r³)/(2 × 10⁻⁷) = (0.3 × 10⁻⁴ × (0.2)³)/(2 × 10⁻⁷) = 2.4 × 10⁻⁴ A·m²
M = (Bₑ r³)/(2 × 10⁻⁷) = (0.3 × 10⁻⁴ × (0.2)³)/(2 × 10⁻⁷) = 2.4 × 10⁻⁴ A·m²
29. The magnetopause is defined as:
Correct Answer: (b) The surface where Earth's magnetic field pressure balances the solar wind pressure
The magnetopause is the boundary between Earth's magnetosphere and the solar wind, where the dynamic pressure of the solar wind equals the magnetic pressure of Earth's field.
30. The value of angle of dip is zero at the magnetic equator because on it
Correct Answer: (c) The value of V is zero
At the magnetic equator, the vertical component (V) of Earth's magnetic field is zero (the field is entirely horizontal), making the angle of dip zero. The horizontal component (H) is maximum here.
31. At a place, the horizontal and vertical intensities of earth's magnetic field is 0.30 Gauss and 0.173 Gauss respectively. The angle of dip at this place is
Correct Answer: (a) 30°
tanθ = V/H = 0.173/0.30 ≈ 0.577 ⇒ θ = tan⁻¹(0.577) ≈ 30°
32. If the angles of dip at two places are 30° and 45° respectively, then the ratio of horizontal components of earth's magnetic field at the two places will be
Correct Answer: (a) √3 : √2
H = I cosθ ⇒ H₁/H₂ = cosθ₁/cosθ₂ = cos(30°)/cos(45°) = (√3/2)/(1/√2) = √3/√2
33. The main difference between the geomagnetic poles and the magnetic dip poles is:
Correct Answer: (c) Geomagnetic poles are based on the best dipole fit, while dip poles are actual measurement points
Geomagnetic poles are calculated based on a theoretical dipole that best fits Earth's field, while magnetic dip poles are actual locations where the field is vertical (dip = ±90°). These can differ by hundreds of kilometers.
34. The magnetic compass is not useful for navigation near the magnetic poles because
Correct Answer: (b) The magnetic field near the poles is almost vertical
Near the magnetic poles, Earth's field is nearly vertical, so there's very little horizontal component to align the compass needle. The needle tends to dip steeply rather than point horizontally.
35. The intensity of Earth's magnetic field is typically measured in:
Correct Answer: (b) Gauss (G) or nanoteslas (nT)
Earth's magnetic field is relatively weak, so it's typically measured in gauss (1 G = 10⁻⁴ T) or nanoteslas (1 nT = 10⁻⁹ T). The field ranges from about 25,000-65,000 nT at Earth's surface.
36. At the magnetic north pole of the earth, the value of horizontal component of earth's magnetic field and angle of dip are, respectively
Correct Answer: (a) Zero, maximum
At the magnetic poles, the field is entirely vertical (dip = 90°), so the horizontal component is zero. The vertical component and total intensity are maximum here.
37. The magnetic field strength in Earth's outer core is estimated to be:
Correct Answer: (b) 10-100 times stronger than at the surface
While direct measurements aren't possible, geodynamo models suggest the magnetic field in Earth's outer core is about 25 Gauss (2.5 mT), roughly 50 times stronger than at the surface.
38. Ratio between total intensity of magnetic field at equator to poles is
Correct Answer: (b) 1 : 2
At poles: I = √(H² + V²) = V (since H=0)
At equator: I = H (since V=0)
For a dipole field, V(pole) = 2H(equator) ⇒ I(equator)/I(pole) = 1/2
At equator: I = H (since V=0)
For a dipole field, V(pole) = 2H(equator) ⇒ I(equator)/I(pole) = 1/2
39. The line on the earth's surface joining the points where the field is horizontal is
Correct Answer: (d) Magnetic equator
The magnetic equator is the line where the magnetic field is entirely horizontal (dip = 0°). It roughly follows the geographic equator but with some deviations.
40. The time between successive geomagnetic polarity reversals is typically:
Correct Answer: (d) Extremely irregular, averaging about 300,000 years
Geomagnetic reversals occur irregularly, with an average interval of about 300,000 years, but the actual time between reversals varies from tens of thousands to millions of years.
41. At a place the earth's horizontal component of magnetic field is 0.3 G. If the angle of dip at that place is 60°, then the vertical component of earth's field at that place in weber/m² will be approximately
Correct Answer: (d) 0.52 × 10⁻⁴
V = H tanθ = 0.3 × tan(60°) = 0.3 × √3 ≈ 0.52 G
1 G = 10⁻⁴ T = 10⁻⁴ Wb/m² ⇒ V ≈ 0.52 × 10⁻⁴ Wb/m²
1 G = 10⁻⁴ T = 10⁻⁴ Wb/m² ⇒ V ≈ 0.52 × 10⁻⁴ Wb/m²
42. The magnetic Reynolds number in geodynamo theory is important because:
Correct Answer: (a) It determines the ratio of advection to diffusion of magnetic flux
The magnetic Reynolds number Rm = μ₀σvL compares the rate of magnetic flux advection (transport by fluid motion) to magnetic diffusion, where μ₀ is permeability, σ is conductivity, v is velocity, and L is length scale.
43. At a place, the magnitudes of the horizontal component and total intensity of the magnetic field of the earth are 0.3 and 0.6 Oersted respectively. The value of the angle of dip at this place will be
Correct Answer: (a) 60°
H = I cosθ ⇒ cosθ = H/I = 0.3/0.6 = 0.5 ⇒ θ = cos⁻¹(0.5) = 60°
44. In two separate experiments the neutral points due to two small magnets are at a distance of r and 2r in broad side-on position. The ratio of their magnetic moments will be
Correct Answer: (d) 1 : 8
For broadside-on position: B = (μ₀/4π)(M/d³) = Bₑ (Earth's field)
M ∝ d³ ⇒ M₁/M₂ = (r)³/(2r)³ = 1/8
M ∝ d³ ⇒ M₁/M₂ = (r)³/(2r)³ = 1/8
45. The angle of dip is the angle
Correct Answer: (c) Between the earth's magnetic field direction and horizontal direction
The angle of dip (or inclination) is the angle that Earth's magnetic field makes with the horizontal plane. It ranges from 0° at the magnetic equator to ±90° at the magnetic poles.
46. The magnetic field due to the earth is closely equivalent to that due to
Correct Answer: (b) A magnetic dipole placed at the centre of the earth
To first approximation, Earth's magnetic field resembles that of a giant bar magnet (dipole) at Earth's center, tilted about 11° from the rotation axis. However, there are significant non-dipole components.
47. The value of the horizontal component of the earth's magnetic field and angle of dip are 0.3 G and 30° respectively at some place. The total intensity of earth's magnetic field at that place will be
Correct Answer: (c) 0.35 G
I = H/cosθ = 0.3/cos(30°) = 0.3/0.866 ≈ 0.35 G
48. The main reason Earth's magnetic field is important for life is because it:
Correct Answer: (b) Shields the atmosphere from solar wind erosion
Earth's magnetic field deflects most of the charged particles in the solar wind, preventing them from stripping away the atmosphere (as happened on Mars) and reducing harmful radiation at the surface.
49. The angle of dip at a place on the earth gives
Correct Answer: (d) The direction of the earth's magnetic field
The angle of dip indicates the direction of Earth's magnetic field relative to the horizontal plane. Combined with declination (direction in horizontal plane), it completely specifies the field's direction.
50. The vertical component of the earth's magnetic field is zero at a place where the angle of dip is
Correct Answer: (a) 0°
When the angle of dip is 0°, the magnetic field is entirely horizontal, so the vertical component is zero. This occurs at the magnetic equator.