# Gravity & Magnetic Surveying

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This Quiz contains the questions from the basics and applications of Gravity and Magnetic methods used in Geophysical Investigations. Enjoy the Quiz n Tk cr. . . . . Be Happy. . . All the best. . . . .

• 1.

### Gravity field variations on the surface :

• A.

Reflects the density variation laterally in the subsurface

• B.

Reflects the density variation vertically in the subsurface

• C.

Do not reflect density variation

• D.

Reflect topogrphic variations only

A. Reflects the density variation laterally in the subsurface
Explanation
Gravity field variations on the surface can be used to infer the density variation laterally in the subsurface. This is because the gravitational pull experienced at different points on the surface is influenced by the distribution of mass beneath the surface. Areas with higher density materials will have a stronger gravitational pull, while areas with lower density materials will have a weaker gravitational pull. Therefore, by measuring and analyzing the gravity field variations, we can gain insights into the density variations in the subsurface.

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• 2.

### Sensitivity of a Gravimeter is :

• A.

0.01 mgal

• B.

0.1 mgal

• C.

0.002 mgal

• D.

0.001 mgal

A. 0.01 mgal
Explanation
The sensitivity of a gravimeter refers to its ability to detect small changes in gravity. A sensitivity of 0.01 mgal means that the gravimeter can accurately measure changes in gravity as small as 0.01 milligals. This level of sensitivity is considered to be quite high, allowing for precise measurements in gravity surveys and other applications where small variations in gravity need to be detected.

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• 3.

### Optical Pumping magnetometer works on the pinciple of:

• A.

Doppler effect

• B.

Proton Precession

• C.

Magnetic saturation

• D.

Zeeman effect

D. Zeeman effect
Explanation
The Zeeman effect is the correct answer because an Optical Pumping magnetometer works by using light to excite atoms in a magnetic field. The Zeeman effect refers to the splitting of spectral lines in the presence of a magnetic field, which is the basis for the operation of the magnetometer. By measuring the frequency shift of the split spectral lines, the magnetometer can determine the strength and direction of the magnetic field.

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• 4.

### The half width of vertical magnetic intensity anomaly over a magnetised sphere is 25 meters .  Calculate the depth to the center of sphere from surface ??

• A.

32.5 m

• B.

50 m

• C.

25 m

• D.

None of these

B. 50 m
Explanation
For sphere : Z = 2 * (X half)

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• 5.

### Van allen zones form at :

• A.

North Pole

• B.

South Pole

• C.

North and South both

• D.

Equator

C. North and South both
Explanation
Van Allen zones form at both the North and South poles. These zones are regions of charged particles trapped by the Earth's magnetic field. They are named after James Van Allen, the scientist who discovered them. The charged particles in these zones are mainly protons and electrons, and they are held in place by the Earth's magnetic field. The Van Allen zones play a crucial role in protecting the Earth from harmful solar radiation by trapping and deflecting it away from the planet.

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• 6.

### The scale of Geodetic Survey is :

• A.

1:250000

• B.

1:10000

• C.

1:5000

• D.

1:50000

A. 1:250000
Explanation
The scale of Geodetic Survey is 1:250000, which means that one unit on the map represents 250,000 units on the ground. This scale is commonly used for large-scale maps that cover a large area, such as regional or national maps. The smaller the denominator of the scale, the larger the area covered by the map but with less detail. Therefore, a scale of 1:250000 indicates a map with a relatively large coverage area but with less detail compared to smaller scale maps.

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• 7.

### At magnetic equator, the inclination of total magnetic field is :

• A.

90 degree

• B.

60 degree

• C.

45 degree

• D.

0 degree

D. 0 degree
Explanation
At the magnetic equator, the inclination of the total magnetic field is 0 degrees. This means that the magnetic field lines are parallel to the Earth's surface at the magnetic equator. There is no vertical component to the magnetic field at this location.

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• 8.

### A gravity profile across a schist belt within a Granitic country rock will give rise to a :

• A.

Central low

• B.

Central High

• C.

Response is flat

• D.

High and Low at the edges

B. Central High
Explanation
A gravity profile across a schist belt within a Granitic country rock will give rise to a Central High. This is because schist is a denser rock compared to the surrounding granitic country rock. The higher density of the schist causes a gravitational attraction that results in a higher gravity reading or anomaly in the central part of the profile.

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• 9.

### Which of the following is non-magnetic ???

• A.

Granite

• B.

Gabbro

• C.

Limestone

• D.

Diorite

C. Limestone
Explanation
Limestone is non-magnetic because it does not contain any magnetic minerals. It is primarily composed of the mineral calcite, which does not have magnetic properties. In contrast, granite, gabbro, and diorite may contain magnetic minerals such as magnetite or hematite, which give them magnetic properties.

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• 10.

### A large sedimenary basin 2 km deep with density contrast of 0.3 gm/cc will approximately give rise to gravity anomaly of :

• A.

5 mgal

• B.

15 mgal

• C.

25 mgal

• D.

50 mgal

C. 25 mgal
Explanation
Apply bouguer formulla

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• 11.

### Relationship of geometrical and gravitational flattening of Earth is given by :

• A.

Gauss Theorem

• B.

Green's Theorem

• C.

Hayford's Theorem

• D.

Clairaut's Theorem

D. Clairaut's Theorem
Explanation
Clairaut's Theorem relates the geometrical flattening of the Earth's shape to the gravitational flattening. It states that the difference between the equatorial and polar radii of the Earth is directly proportional to the square of the angular velocity of the Earth's rotation. This means that as the Earth rotates faster, the difference between its equatorial and polar radii increases, resulting in a more pronounced flattening. Therefore, Clairaut's Theorem provides an explanation for the relationship between the geometrical and gravitational flattening of the Earth.

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• 12.

### The Bouguer anomaly over an isostatically compensated region is :

• A.

Zero

• B.

Positive

• C.

Negative

• D.

Same as isostatic anomaly

A. Zero
Explanation
The Bouguer anomaly over an isostatically compensated region is zero because isostatic compensation refers to the equilibrium between the lithosphere and asthenosphere, where the mass of the crust is balanced by the buoyancy of the underlying mantle. This balance results in no gravitational anomaly, hence the Bouguer anomaly is zero.

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• 13.

### Magnetic equator coincides with the Geomagnetic equator.

• A.

True

• B.

False

B. False
Explanation
The statement is false because the magnetic equator does not coincide with the geomagnetic equator. The geomagnetic equator is the imaginary line on the Earth's surface where the magnetic field is horizontal, while the magnetic equator is the line along which the Earth's magnetic field is strongest. These two lines do not align with each other, so the statement is incorrect.

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• 14.

### SI unit of manetic induction is

• A.

Tesla

• B.

Gauss

• C.

Oesterd

• D.

None of above

A. Tesla
Explanation
The SI unit of magnetic induction is Tesla. Tesla is a unit of measurement for the strength of a magnetic field. It is named after Nikola Tesla, a renowned physicist and inventor. Magnetic induction refers to the density of magnetic field lines passing through a given area. Tesla is a commonly used unit in scientific and engineering applications to quantify magnetic fields and their effects. Gauss, Oesterd, and None of the above are not the correct units for measuring magnetic induction.

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• 15.

### The magnetic domains are due to :

• A.

Covalent bonds

• B.

Doping

• C.

Hysteresis loss

• D.

Spin excange interaction

D. Spin excange interaction
Explanation
The correct answer is spin exchange interaction. Spin exchange interaction refers to the interaction between the spins of neighboring atoms or ions in a material. This interaction can cause the alignment of the spins in a particular direction, leading to the formation of magnetic domains. In these domains, the spins of the atoms or ions are aligned in the same direction, creating a magnetic field. This phenomenon is responsible for the magnetic properties of materials. Covalent bonds, doping, and hysteresis loss are not directly related to the formation of magnetic domains.

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• 16.

### Terrain correction is not generally applied to magnetic field data .

• A.

True

• B.

False

A. True
Explanation
Terrain correction is not generally applied to magnetic field data because magnetic field measurements are not significantly affected by variations in the topography of the land. The magnetic field is primarily influenced by subsurface geological structures and materials, such as rocks and minerals, rather than surface features. Therefore, the need for terrain correction, which is the adjustment of data to account for variations in elevation, is not typically necessary for magnetic field data.

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• 17.

### Curie point temperature for Haematite is :

• A.

578 degree celsius

• B.

670 degree celsius

• C.

550 degree celsius

• D.

None of these

B. 670 degree celsius
Explanation
The Curie point temperature is the temperature at which a material undergoes a phase transition from being ferromagnetic to paramagnetic. Haematite is a mineral that exhibits ferromagnetic properties. Therefore, the correct answer is 670 degree celsius, as this is the temperature at which haematite loses its ferromagnetic properties and becomes paramagnetic.

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• 18.

### Which of the following exhibits negative magnetic susceptibility ???

• A.

Pyroxene

• B.

Quartz

• C.

Olivine

• D.

Biotite

B. Quartz
Explanation
Quartz exhibits negative magnetic susceptibility because it has a diamagnetic property. This means that when placed in a magnetic field, it generates a magnetic field in the opposite direction, causing a repulsive force. Diamagnetic materials have all their electrons paired up and do not have any unpaired electrons to align with the external magnetic field. Therefore, quartz is the correct answer as it shows a negative response to the magnetic field.

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• 19.

### To derive magnetic field from gravity field , the poisson relation can be used only when the direction of magnetization is :

• A.

Horizontal ( 0 degree)

• B.

45 degree

• C.

60 degree

• D.

Vertical ( 90 degree)

D. Vertical ( 90 degree)
Explanation
The Poisson relation can be used to derive the magnetic field from the gravity field only when the direction of magnetization is vertical (90 degrees). This means that the magnetic field is perpendicular to the gravity field. The Poisson relation is a mathematical equation that relates the magnetic field and the gravity field, and it assumes a specific orientation of magnetization. In this case, the vertical direction satisfies the conditions for the Poisson relation to be applicable.

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• 20.

### Gravity measurement is made on a ship sailing at the speed of 6 knots in the direction N650E at 200N latitude. The Eotvos correction (in mGal) is :

• A.

+ 38.5

• B.

+ 24.5

• C.

- 35.5

• D.

-39.5

A. + 38.5
Explanation
If vehicle moves in same direction as earth... then eovtos correction is added because of reduced gravity value.

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• Current Version
• Mar 21, 2023
Quiz Edited by
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• May 02, 2014
Quiz Created by
Kapil_IITR

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