General Principles in the Working of Mariner's Compass, Lightning Conductors
General Principles in the Working of Mariner's Compass, Lightning Conductors MCQ Questions
1.
What is the primary function of a mariner’s compass?
ANSWER :
B. Determining direction
Approach
The question asks for the primary function of a mariner's compass. This requires knowledge of basic navigational tools and their uses. A mariner's compass is a fundamental instrument used in navigation.
Step-by-step
- Understand the purpose of a compass: A compass, in general, is a navigational instrument that shows directions relative to the geographic cardinal directions (North, South, East, West).
- Consider the term "mariner's compass": The term "mariner's" specifically refers to its use by sailors or in marine navigation. On the open sea, without landmarks, determining direction is crucial for safe passage.
- Evaluate the options:
- A) Measuring temperature: Temperature is measured by a thermometer, not a compass.
- B) Determining direction: This aligns perfectly with the primary function of any compass, especially a mariner's compass, which uses Earth's magnetic field to point to magnetic north.
- C) Calculating distance: Distance is typically calculated using speed and time, or by measuring positions on a chart, not directly by a compass.
- D) Predicting weather: Weather prediction involves various meteorological instruments and observations, not a compass.
- Conclude the primary function: Based on the evaluation, the most accurate and primary function of a mariner's compass is to determine direction.
Correct Option:
B) Determining direction — A mariner's compass is a crucial navigational tool that uses the Earth's magnetic field to indicate magnetic north, thereby allowing sailors to determine their bearing and navigate effectively.
Incorrect Options
- A) Measuring temperature — Temperature is measured using a thermometer, which is a different instrument altogether and not related to a compass's function.
- C) Calculating distance — Distance is typically calculated using other methods like dead reckoning (speed multiplied by time) or by plotting positions on a chart, not directly by a compass.
- D) Predicting weather — Weather prediction relies on meteorological instruments such as barometers, anemometers, and satellite data, not a compass.
2.
Which component of the mariner’s compass is responsible for pointing north?
Approach
The question asks to identify the specific component of a mariner's compass that is responsible for indicating the North direction. This requires knowledge of the basic construction and function of a magnetic compass.
Step-by-step
- A mariner's compass, like any magnetic compass, works on the principle that a freely suspended magnet aligns itself with the Earth's magnetic field.
- The Earth acts like a giant magnet, creating a magnetic field that extends into space.
- The component within the compass that is actually magnetized and thus responds to the Earth's magnetic field is the needle.
- This needle is typically made of a ferromagnetic material and is magnetized, allowing one end to point towards the Earth's magnetic North Pole and the other towards the South Pole.
- The other components listed have different functions in the compass's operation.
Correct Option: B) The needle is the magnetized component of the compass that aligns itself with the Earth's magnetic field, thereby pointing towards magnetic north.
Incorrect Options
- A) Card — The card (or compass card) is a circular disc on which the cardinal points (North, South, East, West) and degrees are marked. It is attached to the needle and rotates with it, allowing the user to read the direction. It does not itself point north; rather, it displays the direction indicated by the needle.
- C) Lubber line — The lubber line is a fixed mark or line on the compass bowl that indicates the fore-and-aft line of the vessel (or the direction the observer is facing). It is used to take a bearing relative to the vessel's heading, not to point north.
- D) Gimbal — A gimbal is a pivoted support that allows an object, such as a compass, to rotate about a single axis. In a mariner's compass, gimbals are used to keep the compass bowl level, regardless of the pitching and rolling of the ship, ensuring the needle can swing freely and accurately. It does not directly point north.
3.
What liquid is often used to dampen the needle in a mariner’s compass?
Approach
The question asks about the liquid used to dampen the needle in a mariner's compass. This involves understanding the properties of liquids suitable for damping mechanisms, especially in instruments like compasses.
Step-by-step
- Purpose of damping: In a compass, the magnetic needle tends to oscillate back and forth before settling on the correct direction. Damping is the process of reducing these oscillations quickly and smoothly, allowing the needle to settle faster and provide a stable reading.
- Properties of a suitable damping liquid: The liquid used for damping should have specific characteristics:
- Low viscosity: To allow the needle to move freely but with resistance.
- Low freezing point: Mariners' compasses are used in various climates, including cold regions, so the liquid should not freeze.
- High boiling point: To prevent evaporation in hot climates.
- Non-corrosive: It should not react with the compass components.
- Good thermal expansion properties: To maintain consistent damping across temperature changes.
- Evaluating the options:
- Mercury: Has a high density and is a good conductor, but its freezing point is relatively high (\(-38.83 \text{ °C}\)) and it's toxic. It's not typically used for damping in compasses.
- Kerosene: While it has a low freezing point, its viscosity can vary significantly with temperature, and it might not provide optimal damping.
- Water: Freezes at \(0 \text{ °C}\), which makes it unsuitable for use in cold environments. It also has a relatively high surface tension and can cause corrosion.
- Alcohol (specifically ethanol or a mixture like denatured alcohol): Has a very low freezing point (ethanol freezes at \(-114.1 \text{ °C}\)), making it ideal for use in cold climates. It also has suitable viscosity for damping and is non-corrosive to most compass materials.
- Conclusion: Alcohol is the most suitable liquid among the given options for damping the needle in a mariner's compass due to its low freezing point and appropriate damping properties.
Correct Option:
D) Alcohol is commonly used to dampen the needle in a mariner's compass. Its low freezing point ensures the compass remains functional in cold temperatures, and its viscosity provides effective damping to quickly settle the needle.
Incorrect Options
- A) Mercury — Mercury is a dense liquid metal with a relatively high freezing point compared to alcohol, making it unsuitable for use in cold climates. It is also toxic.
- B) Kerosene — While it has a lower freezing point than water, its damping properties and temperature stability might not be as ideal as alcohol for precision instruments like a compass.
- C) Water — Water freezes at \(0 \text{ °C}\), which makes it completely impractical for a mariner's compass that needs to function in various temperatures, including freezing conditions.
4.
Which feature of a mariner’s compass helps stabilize it on a moving ship?
Approach
The question asks about the mechanism that stabilizes a mariner's compass on a moving ship. This requires understanding how instruments are kept level or steady despite the motion of their platform.
Step-by-step
- A mariner's compass needs to remain level and stable to provide accurate readings, even when the ship is pitching, rolling, or yawing due to waves or movement.
- A gimbal is a pivoted support that allows an object to rotate about a single axis. A set of two or three gimbals, one mounted on the other with orthogonal pivot axes, can keep an object level regardless of the motion of its support.
- This system effectively isolates the compass from the ship's motion, ensuring it stays horizontal and its needle can freely align with the Earth's magnetic field.
Correct Option:
A) Gimbal — A gimbal is a device that allows an object, such as a compass, to remain in a stable orientation (e.g., horizontal) despite the tilting or movement of its support. This is crucial for accurate navigation on a moving ship.
Incorrect Options
- B) Baseplate — The baseplate is simply the bottom part of the compass housing. It provides structural support but does not actively stabilize the compass against motion.
- C) Mirror — Some compasses have a mirror, often used for sighting bearings or for viewing the compass card simultaneously with the target. It does not contribute to stabilization.
- D) Index line — The index line (or lubber line) is a fixed mark on the compass housing that indicates the direction straight ahead of the ship. It is used to read the ship's heading but does not stabilize the compass.
5.
What does the lubber line on a mariner’s compass indicate?
ANSWER :
A. Direction of travel
Approach
The question asks about the function of a 'lubber line' on a mariner's compass. To answer this, one needs to understand the basic components and working principle of a ship's compass.
Step-by-step
- A mariner's compass is used to determine the ship's heading relative to magnetic north.
- The compass card, which is marked with degrees and cardinal points (N, S, E, W), rotates freely to align with the Earth's magnetic field.
- The ship itself moves, and its direction of travel changes. To relate the ship's direction to the compass card, a fixed reference point is needed on the compass housing.
- This fixed reference point is the lubber line. It is a vertical mark inside the compass bowl that is aligned with the ship's fore-and-aft line (the direction of the ship's bow).
- As the ship turns, the lubber line moves relative to the rotating compass card. The degree mark on the compass card that aligns with the lubber line indicates the ship's current heading or direction of travel.
Correct Option: A) The lubber line on a mariner's compass indicates the direction of travel (or the ship's heading). It is fixed relative to the ship and shows which point on the compass card corresponds to the ship's bow.
Incorrect Options
- B) Magnetic north: The compass needle or card itself points to magnetic north. The lubber line is a fixed reference on the ship, not an indicator of magnetic north.
- C) True north: True north is a geographical direction, different from magnetic north due to magnetic declination. The compass, by itself, points to magnetic north; true north is calculated from magnetic north and declination. The lubber line does not directly indicate true north.
- D) Declination: Declination is the angular difference between magnetic north and true north. It is a correction factor, not something indicated by the lubber line.
6.
What is the main purpose of the compass card in a mariner’s compass?
A.
To adjust magnetic deviation
B.
To provide directional reference
C.
To stabilize the needle
ANSWER :
B. To provide directional reference
Approach
The question asks about the primary function of the compass card in a mariner's compass. Understanding the basic components and working principle of a compass is key to answering this question.
Step-by-step
- A mariner's compass is a navigational instrument that shows direction relative to the geographic cardinal directions (North, South, East, West).
- The core component of a compass is a magnetized needle or element that aligns itself with the Earth's magnetic field.
- The compass card is a circular disk, often marked with degrees (0-360) and cardinal points (N, S, E, W), which is attached to the magnetic needle.
- As the magnetic needle aligns itself with the Earth's magnetic North, the compass card rotates along with it.
- The markings on the compass card then provide a visual reference for the direction in which the vessel is heading or the bearing of an object. For example, if the ship is heading North, the 'N' on the compass card will align with the lubber line (a fixed mark on the compass housing indicating the ship's bow).
Correct Option: B) To provide directional reference
The compass card is essentially the display mechanism of the compass. It has markings (degrees, cardinal points) that rotate with the magnetic element, allowing the user to read the direction relative to magnetic North. This makes its main purpose to provide a clear and readable directional reference.
Incorrect Options
- A) To adjust magnetic deviation — Magnetic deviation is the error induced in a compass by the magnetic fields of the ship itself. It is usually compensated for by placing small magnets near the compass or by using a deviation card, not by the compass card itself. The compass card simply displays the direction, including any deviation present.
- C) To stabilize the needle — While a compass might have damping mechanisms (like liquid filling) to stabilize the needle and prevent excessive oscillation, the compass card's primary role is not stabilization. It is a display component.
- D) To measure speed — A compass is used for navigation and direction, not for measuring speed. Speed is typically measured by other instruments like a log, GPS, or by timing observations.
