SSC JE 2023 Exam: Surveying-What is a Prismatic Compass?

What is a Prismatic Compass?

A prismatic compass is a type of magnetic compass used for navigation and orientation purposes. It is a compact and portable instrument that incorporates a prism and a magnetic needle to determine the direction or bearing of a specific point relative to the user’s position. Prismatic compasses are commonly used by surveyors, geologists, explorers, and military personnel for various applications.

What is a Prismatic Compass?

A prismatic compass is a type of magnetic compass used for navigation and orientation purposes. It is a compact and portable instrument that incorporates a prism and a magnetic needle to determine the direction or bearing of a specific point relative to the user’s position. Prismatic compasses are commonly used by surveyors, geologists, explorers, and military personnel for various applications.

Here are the key components and features of a prismatic compass:

1. Compass Housing: The compass is typically housed in a metal or plastic casing that protects the delicate internal components from external factors like dust and moisture.

2. Magnetic Needle: Inside the compass housing, there is a magnetic needle that is free to rotate. The magnetic needle aligns itself with the Earth’s magnetic field, pointing towards magnetic north.

3. Prism: A prism is mounted above the magnetic needle. The prism allows the user to simultaneously view both the magnetic needle and the target or object being measured. This feature makes it easier to take accurate bearings.

4. Sighting Mechanism: Prismatic compasses often have a sighting mechanism, which consists of sighting vanes. This allows the user to aim the compass accurately at the target.

5. Graduated Ring: Around the edge of the compass housing, there is a graduated ring with degree markings. These markings help the user read the bearing or azimuth (direction) of the target by noting the angle at which the magnetic needle aligns with the markings.

To use a prismatic compass, the user looks through the prism and lines up the target with the sighting mechanism. They then read the bearing or azimuth from the graduated ring where the magnetic needle points.

Prismatic compasses are useful for measuring directions, determining the angles between objects, and creating accurate maps or surveys. They are particularly valuable in situations where precise measurements of direction are required, such as in land surveying, geological exploration, and military navigation.

Q. In a prismatic compass, what does the magnetic needle align with?

   a) True north

   b) Grid north

   c) Magnetic north

   d) Celestial north

Answer: c) Magnetic north Explanation: The magnetic needle within a prismatic compass aligns itself with the Earth’s magnetic field, indicating the direction of magnetic north.

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