General Principles in the Working of Mariner's Compass, Lightning Conductors
General Principles in the Working of Mariner's Compass, Lightning Conductors MCQ Questions
13.
Which method is often used to correct a mariner’s compass for magnetic deviation?
A.
Calibrating with a GPS
B.
Adjusting with a protractor
C.
Using compensating magnets
D.
Immersing in a magnetic fluid
ANSWER :
C. Using compensating magnets
Approach
The question asks about the method used to correct a mariner's compass for magnetic deviation. Magnetic deviation is the error induced in a compass by local magnetic fields on board a ship, such as those from the ship's structure, electrical equipment, or cargo. To counteract these local magnetic influences, specific compensation techniques are employed.
Step-by-step
- A mariner's compass relies on the Earth's magnetic field to indicate direction. However, the magnetic materials and electrical currents within a ship create their own magnetic fields.
- These ship-induced magnetic fields interfere with the Earth's magnetic field, causing the compass needle to point slightly away from magnetic north. This error is known as magnetic deviation.
- To ensure accurate navigation, this deviation must be corrected. The standard method involves introducing additional magnetic fields that counteract the ship's magnetic fields.
- This is achieved by placing small, adjustable magnets (compensating magnets) near the compass. These magnets are carefully positioned and adjusted to nullify the deviation caused by the ship's magnetism.
- The process of adjusting these magnets is called "swinging the ship" or "compass adjustment," where the ship is turned through various headings, and the deviation is measured and corrected.
Correct Option: C) Using compensating magnets
This is the traditional and most effective method for correcting magnetic deviation in a mariner's compass. Compensating magnets are strategically placed around the compass to create opposing magnetic fields that cancel out the ship's magnetic interference, thereby allowing the compass to align more accurately with magnetic north.
Incorrect Options
- A) Calibrating with a GPS — GPS (Global Positioning System) provides positional information and can calculate true course and speed over ground, but it does not directly correct the physical magnetic deviation of a compass. While GPS can be used to determine the actual heading and thus measure the compass error (including deviation), it doesn't physically adjust the compass itself.
- B) Adjusting with a protractor — A protractor is a tool for measuring angles on charts or determining bearings, but it is not used to physically adjust or correct the magnetic deviation of a compass. It's a navigational plotting tool, not a compass adjustment tool.
- D) Immersing in a magnetic fluid — Immersing a compass in a magnetic fluid is not a recognized method for correcting magnetic deviation. Compass bowls are often filled with a non-magnetic, clear liquid (like alcohol or purified water) to dampen oscillations of the compass card, but this fluid does not correct for deviation. A magnetic fluid would likely interfere further with the compass's operation.
14.
What does “compass heading” refer to?
B.
Course set relative to magnetic north
ANSWER :
B. Course set relative to magnetic north
Approach
The question asks for the definition of "compass heading." This term is fundamental in navigation, particularly for ships and aircraft. Understanding the basic principles of navigation, including how direction is measured, is key to answering this question.
Step-by-step
- Understand "Heading": In navigation, "heading" refers to the direction in which the bow (front) of a vessel or aircraft is pointed.
- Understand "Compass": A compass is an instrument used for navigation and orientation that shows direction relative to the geographic cardinal directions (North, South, East, West). There are different types of compasses, primarily magnetic and gyro compasses.
- Combine "Compass" and "Heading": When a compass is used to determine the heading, it provides the direction relative to a specific reference point. For a magnetic compass, this reference point is magnetic north. For a gyro compass, it's true north. The term "compass heading" generally refers to the direction indicated by a magnetic compass.
- Evaluate Options:
- Option A (Direction of wind): While wind direction is important for navigation, it is not what "compass heading" refers to.
- Option B (Course set relative to magnetic north): This aligns perfectly with the definition of a magnetic compass heading, which indicates the direction of the vessel's bow relative to magnetic north.
- Option C (Position of the sun): The sun's position can be used for celestial navigation, but it's not directly what "compass heading" means.
- Option D (Speed of the vessel): Speed is a measure of how fast the vessel is moving, not its direction.
Correct Option: B) Course set relative to magnetic north
A compass heading specifically refers to the direction in which a vessel or aircraft is pointed, as indicated by a compass. For a magnetic compass, this direction is measured relative to magnetic north. This is a fundamental concept in marine and air navigation.
Incorrect Options
- A) Direction of wind — The direction of the wind (or relative wind) is a meteorological factor and is distinct from the vessel's heading. While important for navigation, it is not the definition of "compass heading."
- C) Position of the sun — The position of the sun is used in celestial navigation to determine a vessel's position, but it does not define the "compass heading," which is the direction the vessel is pointing.
- D) Speed of the vessel — Speed is a measure of magnitude (how fast), whereas heading is a measure of direction. These are distinct navigational parameters.
15.
What is the typical reference direction used in a mariner’s compass?
ANSWER :
B. Magnetic north
Approach
The question asks about the typical reference direction used in a mariner's compass. A mariner's compass, like any magnetic compass, operates based on the Earth's magnetic field. Therefore, its primary reference direction is directly related to this field.
Step-by-step
- A mariner's compass is a magnetic compass designed for navigation at sea.
- Magnetic compasses work by aligning a magnetized needle with the Earth's natural magnetic field.
- The Earth's magnetic field lines converge at the magnetic poles. Therefore, the compass needle points towards the magnetic north pole.
- While navigators often convert this reading to true north for charting purposes, the direct reading from the compass itself is magnetic north.
Correct Option: B) Magnetic north
Incorrect Options
- A) True north — True north is the geographical North Pole, which is a fixed point on the Earth's axis of rotation. While navigators aim to determine true north for accurate charting, a magnetic compass does not directly point to true north. There is an angular difference between magnetic north and true north, known as magnetic declination, which varies by location and time.
- C) Grid north — Grid north is a navigational term used in conjunction with map grids, particularly on large-scale maps. It refers to the direction of the north-south grid lines on a map. A compass does not naturally align with grid north; it's a map-specific reference.
- D) Solar north — Solar north is not a standard navigational reference direction. While the sun's position can be used for celestial navigation to determine direction, a mariner's compass does not use the sun as its primary reference.
16.
What is magnetic variation?
A.
The angle between true north and magnetic north
B.
The oscillation of the compass needle
C.
The difference between compass heading and true heading
D.
The fluctuation in Earth's magnetic field
ANSWER :
A. The angle between true north and magnetic north
Approach
The question asks for the definition of magnetic variation. This is a fundamental concept in navigation and geography related to the Earth's magnetic field.
Step-by-step
- Understand True North: True North is the direction along the Earth's surface towards the geographic North Pole. It is a fixed point.
- Understand Magnetic North: Magnetic North is the direction towards the Earth's North Magnetic Pole, which is constantly shifting due to changes in the Earth's core. A compass needle points to Magnetic North.
- Define Magnetic Variation: Since True North and Magnetic North are generally not in the same location, there is an angular difference between them at any given point on the Earth's surface. This difference is known as magnetic variation (or magnetic declination). It is crucial for navigation as it allows navigators to convert between magnetic bearings (read from a compass) and true bearings (used on maps).
Correct Option: A) The angle between true north and magnetic north
This option accurately defines magnetic variation. It is the angular difference between the direction of the geographic North Pole (True North) and the direction indicated by a magnetic compass (Magnetic North) at a specific location.
Incorrect Options
- B) The oscillation of the compass needle — This describes the movement of the compass needle, often due to external forces or instability, not magnetic variation itself.
- C) The difference between compass heading and true heading — This concept is related to magnetic variation but also includes magnetic deviation (errors caused by magnetic fields within the vessel or aircraft). Magnetic variation is specifically the difference between magnetic north and true north, which is then applied to convert magnetic heading to true heading.
- D) The fluctuation in Earth's magnetic field — While the Earth's magnetic field does fluctuate (secular variation), this option describes the change in the field over time, not the static angular difference at a given moment that is defined as magnetic variation.
17.
How can magnetic deviation affect a mariner’s compass?
A.
By stabilizing the needle
B.
By causing errors due to local magnetic fields
D.
By making the compass needle point to true north
ANSWER :
B. By causing errors due to local magnetic fields
Approach
The question asks about the effect of magnetic deviation on a mariner's compass. Magnetic deviation refers to the error in a compass reading caused by magnetic fields originating from the ship itself. Understanding this concept is key to identifying the correct answer.
Step-by-step
- Understand Magnetic Deviation: Magnetic deviation is the angular difference between the magnetic north indicated by a ship's compass and the actual magnetic north. This difference arises because the ship's metallic structure, electrical equipment, and cargo can generate their own magnetic fields.
- Impact on Compass: These local magnetic fields interact with the Earth's magnetic field, causing the compass needle to be deflected from its true magnetic alignment.
- Consequence for Navigation: This deflection means the compass does not accurately point to magnetic north, leading to errors in the observed bearing and, consequently, in navigation. Mariners must account for this deviation to plot an accurate course.
- Evaluate the Options:
- Option A suggests stabilization, which is incorrect as deviation introduces instability in accurate readings.
- Option B directly addresses the core issue: errors due to local magnetic fields.
- Option C suggests improved accuracy, which is the opposite of what deviation does.
- Option D suggests pointing to true north, which is incorrect. A compass points to magnetic north (after correcting for deviation and variation), not true north, unless magnetic declination (variation) is zero.
Correct Option:
B) By causing errors due to local magnetic fields. Magnetic deviation is precisely the error introduced in a compass reading by the magnetic fields generated by the ship's structure, machinery, and cargo. These local fields interfere with the Earth's magnetic field, causing the compass needle to point incorrectly.
Incorrect Options
- A) By stabilizing the needle — Magnetic deviation does not stabilize the needle; instead, it introduces an error, making the reading less stable in terms of accuracy relative to magnetic north.
- C) By improving accuracy — Magnetic deviation reduces the accuracy of the compass by deflecting the needle from the true magnetic north. Mariners must correct for deviation to improve accuracy.
- D) By making the compass needle point to true north — A magnetic compass, even without deviation, points to magnetic north, not true north. True north is a geographical direction, while magnetic north is the direction of the Earth's magnetic field lines. Deviation further complicates this by making the compass point away from even magnetic north.
18.
What is the purpose of a deviation card?
A.
To record corrections for compass errors
B.
To log GPS coordinates
C.
To calculate wind speed
D.
To measure water depth
ANSWER :
A. To record corrections for compass errors
Approach
The question asks about the purpose of a deviation card. This is a specific term used in navigation, particularly with magnetic compasses. Understanding the challenges associated with magnetic compasses in vessels helps to identify the correct function of a deviation card.
Step-by-step
- Understand Magnetic Compass Limitations: A magnetic compass points to magnetic north. However, metallic structures, electrical equipment, and other magnetic fields within a ship or aircraft can interfere with the compass, causing it to point inaccurately. This error is known as magnetic deviation.
- Define Deviation: Deviation is the error in a magnetic compass caused by magnetic influences within the vessel itself. This error varies depending on the vessel's heading.
- Purpose of a Deviation Card: To ensure accurate navigation, these deviation errors must be known and accounted for. A deviation card is a table or graph that lists the deviation for various headings of the vessel. It is created by 'swinging the compass,' a process where the vessel is steered through 360 degrees, and the compass readings are compared against known true or magnetic bearings.
- Applying Corrections: Navigators use the deviation card to apply corrections to their compass readings, converting the compass heading to magnetic heading, which can then be converted to true heading using magnetic variation data.
Therefore, the primary purpose of a deviation card is to record and provide corrections for the errors inherent in a magnetic compass due to the vessel's own magnetic fields.
Correct Option: A) To record corrections for compass errors
Incorrect Options
- B) To log GPS coordinates — GPS (Global Positioning System) provides highly accurate positional data and does not rely on magnetic compasses or deviation cards for its operation. GPS coordinates are logged separately.
- C) To calculate wind speed — Wind speed is typically measured using an anemometer or estimated from weather data, not using a deviation card. A deviation card is related to compass accuracy, not atmospheric conditions.
- D) To measure water depth — Water depth is measured using a fathometer or echo sounder. A deviation card has no role in determining water depth.
