How Does a Compass Work

Last Updated on August 29, 2018

How Does a Compass Work

History and applications

The compass is a measuring instrument to orient oneself, by locating magnetic North. Chinese invention, its date of creation is still a little obscure. However, writings dating back to the 4th century BC and the year 70 already dealt with magnetism.

It was not until the 11th century that the ancestor of the compass made its appearance. Called “fish pointing south,” it is described as an iron fish floating in a bowl of water. This technique is highlighted in the book “General Principles of the Classic of War” from the time of the Song Chinese Dynasty.

In his book “Pingzhou Ketan” , author Zhu Yu states in 1117: “The navigator knows the geography, he observes the stars at night, he observes the sun during the day; when the sky is dark and cloudy, he looks at the compass”.

This attests the existence and use of the compass (or compass) in marine navigation. The sultan and astronomer Al-Ashraf would turn, causing its use in astronomy, since 1282.

Composition and operation

To understand the operation of a compass, it is important to start with the one of the Earth. It is composed of two geomagnetic poles and a magnetic field, acting like a magnet. This one interacts with the one contained in the compass to give the magnetic north.

Thus, the magnetic north of the Earth attracts the south pole of the magnet. The opposite direction will be magnetic north, which is to be differentiated from the geographic North Pole. The magnetic south pole is off Adelie Land when the magnetic north pole is more than 1000 kilometers from the North Pole to Canada.

On the other hand, terrestrial magnetic declination is the difference between these two data. If this difference is minimal in France, it can clearly differ especially at sea. That’s why there are different types of compasses. In the northern hemisphere, the tip of the southern needle of the compass is lightly weighted.

The lines of the Earth’s magnetic field are not on the Earth’s surface but well below, the needle is automatically drawn down. Also, this acts as a counterweight.

On the other hand, a compass used in Europe will constantly turn or will remain blocked in the southern hemisphere of the planet, because of this ballasting. It is therefore mandatory to use a compass specific to the southern hemisphere.

For marine navigation, it is the compass that acts as a compass. Working on the same principle, the wind rose is this time on the surface of a viscous liquid, to stabilize the needle at magnetic north.

The pivot

It allows the needle on it to rotate without friction, which could lead to an incorrect indication.

The needle

C ‘is a magnet with two poles: north and south. The tip indicating magnetic north is often colored red or with fluorescent paint. When dealing with magnetic fields, do not use a compass near power lines or metal objects such as signs.

The dial

It is graduated in degrees (from 0 to 360 °). It is also divided into quadrants representing 90 ° and the four cardinal points (north, south, east, west).

These quadrants can also be divided into two, indicating north-east (NE), south-east (SE), southwest (SW) and north-west (NW), and usually turns to memorize the position and is often transparent, so that it can read a map by placing it on it.

In summary

  • The magnetic poles of the compass needle react with the magnetic poles of the Earth.
  • The magnetic pole is different from the geographical pole.
  • A compass used in the northern hemisphere of the planet will not work in the southern hemisphere, because of the ballasting of the needle.
  • Do not use a compass near power lines or metal objects.
  • The compass is a kind of compass whose needle is suspended in a viscous liquid, in order to stabilize it. It is used for navigation.


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