# What is Compass: Definition and 87 Discussions

A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with magnetic north. Other methods may be used, including gyroscopes, magnetometers, and GPS receivers.
Compasses often show angles in degrees: north corresponds to 0°, and the angles increase clockwise, so east is 90°, south is 180°, and west is 270°. These numbers allow the compass to show azimuths or bearings which are commonly stated in degrees. If local variation between magnetic north and true north is known, then direction of magnetic north also gives direction of true north.
Among the Four Great Inventions, the magnetic compass was first invented as a device for divination as early as the Chinese Han Dynasty (since c. 206 BC), and later adopted for navigation by the Song Dynasty Chinese during the 11th century. The first usage of a compass recorded in Western Europe and the Islamic world occurred around 1190.

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1. ### B How does a compass know that it is in a magnetic field?

Sorry for this question: how does a compass (or its electrons) know that it is in a magnetic field? Is it the information of the photons that cross it? (photons are what transmit electromagnetic forces)
2. ### B Can a Compass Needle be Magnetized to Any Horizontal Direction?

A compass needle can be magnetized to point to the north. Am I correct in thinking that the needle could have been magnetized to point to any other horizontal direction?
3. ### Geometric Construction (bisecting an angle with a compass and straightedge)

In discussing flight mechanics with a (15 years younger) co-worker with a doctorate in Aerospace Engineering. We examined some angles and I happened to mention bisecting an angle. I told him in High School in the early 1970's we learned how to bisect an angle with compass, and straightedge...
4. ### MHB Compute Image Gradient Intensity - No Noise

Hello guys, if I have an image with 11x11 pixels and in the center of the image is a square of 5x5 pixels, with the gray level of the background 0 and the gray level of the square is 50. How can I compute the result of the magnitude of edges(intensity of the contour) or better said the gradient...
5. ### Compass , current carrying coil

a. No, because only permanent magnets are suitable to be used as a compass. b. Yes, but only if the coil doesn't have an iron core. c. Yes, but only if the coil can turn easily. I choose (c) , Is that correct ?
6. ### MHB How to divide a circumference into equal parts, WITHOUT COMPASS?

Hi guys I have the length of a circumference, how do you divide it into equal parts given a certain amount of parts? For example, I want to divide a circumference into 78 equal parts, and the circumference diameter is 1 meter! Whats the length of each part? And how do you calculate it? (no...
7. ### How Do Digital Compasses in Watches Measure Direction?

Hi. I am curious to know how a digital compass in wristwatches works. How do they get the direction of the Earth magnetic field? I know the coils can measure the value,but how does they get the direction? Casio's site explain like this: "The magnetic field of the Earth is a complex network of...
8. ### Other Correction to a book (magnetic compass)

This article (in the picture) states that the end of a compass needle which points toward North is its south pole since the Earth's "magnet" has a North magnet at the North. But in reality, there is a south magnet pole (not sure about that terminology) near Earth's North Pole, attracting all...
9. U

### How rubbing a needle on a magnet affects its polarity

Homework Statement It is known that when rubbing a needle on a magnet, the needle will become magnetized. If you rub the needle on the north side of the magnet, will it point differently than if you rubbed it on the south side of the magnet? Does it matter what direction you rub the needle...
10. ### What direction will a compass point at point X?

Homework Statement The plotting compass, initially on the left and pointing to the geographical north, is now placed at point X. Which direction it will show? Homework EquationsThe Attempt at a Solution I think the arrow will point towards the south pole of the bar magnet (to the left). Is...
11. ### Magnetic compass and Earth's magnetic field

Hello , I am having a slight confusion while reading the chapter on Earth's magnetism . If we place a magnetic compass on the floor I.e on Earth's surface , the North (red) of the compass needle points towards magnetic north of Earth . But would it be correct to say that "the compass needle...
12. ### What direction does a compass point to in a magnetic field?

Hello Today we did a lab and one of the activities was having a compass underneath a wire while the current was off. The wire was straight so that it was directly aligned to be with the needle of the compass. One the current was flowing, the compass arranged itself in that it was not exactly 90...
13. ### B Universal Compass Speedometer Redux: Relativistic Doppler?

Could relativistic Doppler, as in measuring the cosmic microwave background's wavelength from all directions, be used to determine one's velocity and direction in space? With maybe a gyroscopic device initialized to some arbitrary x,y,z grid?
14. ### B Can we build a four dimensional compass?

The reason I ask is that when we use the surface of the Earth as an analogy, if we travel in one direction then eventually we will come back to where we started. But to do that we need a compass or some similar instruments to keep track of our path to make sure we are always in a "straight"...
15. ### Writing: Input Wanted A Magic Compass & Real Magnetism

Hello! I'm looking for some help regarding magnetism and how it might work (or be fictionalized) in regards to a "magic" compass. I have two questions. Please excuse my complete scientific ignorance :) In my story, our young hero has a compass. The compass needle just spins in endless...
16. ### Distance of compass to wire based on magnetic field strength

Homework Statement As shown in Figure 1 below, a long, straight conducting wire is stretched horizontally directly above a magnetic compass, both of which are separated by distance d. When electrical current is not flowing through the wire, the compass needle points in a direction parallel with...
17. ### MHB Measuring Hollow Sphere Diameter with Compass & Ruler

Using only a compass and a ruler, how can we measure the diameter of a hollow sphere?
18. ### MHB From a sketch to the compass ; Geometric construction

This is a rough sketch, (Happy) Now apart from constructing the triangle can you help me to located the point D & Obtain the location of point E on side AB such that ACDE is a trapezium ,only using an straight edge and a compass. (Crying)
19. ### B Does a Compass Point to Geographic South Below Earth's Surface?

since magnetic field lines form closed loops , field inside Earth must be due geographic south will compass below Earth's surface point to geographic south?
20. ### A Challenge: splitting an angle into three equal parts

I recently decided to take a whack at this problem. Came up with an interesting approach, thought it would make a good conversation topic. Anyone else tried to do this? What were your results?
21. ### Does electric fields affect a compass

By electitc field, i do not mean the magnetic field produced by a current carrying wire, but rather between charged particles. If a compass is placed between the electric field, will the compass needle delfect or will it just continue pointing in the initial direction?
22. ### Homework help -- magnetic field from a wire causing compass deflection....

Homework Statement A current 2A flows in a wire. Value of horizontal component of Earth magnetic field in the region is 2x10^-5T. Small compass placed 5cm due north of the wire. Calculate the angle through which the needle deflects due to the current flowing in the wire. Assume u0= 4pi x 10^-7...
23. ### Alignment of the compass needle

If a compass is placed above a current carrying wire, why does the compass needle align itself in the direction of the magnetic field produced by the wire?
24. ### Why Does a Compass Needle Deflect Between Opposing Currents?

hi, i know this question is a bit unnecessary but i just want to know if i got my concept right so, here's the question if you have a compass pointing northwards placed between two parallel wires carrying opposite current, does the needle deflect? my answer is the needle won't deflect since the...
25. ### Compass Behavior Near Parallel Current-Carrying Wires

Homework Statement two wires are parallel to each other,carries current of same magnitude, and the distance between them is 10cm ,, wire A carries current out of the page ,, Wire B carries current into the page ... A compass is placed at 4 cm from wire A .. Where does the needle point ? I...
26. ### Compass needle, magnetic field and current

Homework Statement Eric looks at his compass to check the direction to north. At a point two (2.0) meters below Eric, a cable is drawn from south to north and the current running through the cable is 50 Amperes. This current makes the compass needle turn wrong. How big is the angle deviation if...
27. ### Moment of Inertia Compass Needle

Homework Statement You place a magnetic compass on a horizontal surface, allow the needle to settle, and then give the compass a gentle wiggle to cause the needle to oscillate about its equilibrium position. The oscillation frequency is 0.321 Hz. Earth's magnetic field at the location of the...
28. ### Battery alone deflects compass needle?

Homework Statement I'm an introductory electromagnetism course and in lab we were observing how an electric current could deflect a compass needle. however, i also noticed that the batter itself (with no wire attached, so no current) could also deflect the needle. (for ex, if you brought the...
29. ### Determining Compass Bearing from Resultant Angle

We are using a smart phone app to add vectors; once we get the resultant angle, we need to determine what direction the vector is based on the compass. Can someone easily explain how to do this? Example: Using the app, we input a 2 knot current toward 230 degrees and a 0.7 knot wind speed...
30. ### Deviation of compass in another frame

Consider an inertial frame where an electric current is flowing in upward direction, a magnetic field is created and its direction is determined by the right hand rule. In the frame of reference of the electric charges which they are at rest, how can the observer in that frame explains the...
31. ### Simulating the wigglyness of a compass pin

Hey guys :) I'm working on a little bar magnet and compass simulation. You can see my progress here: https://dl.dropboxusercontent.com/u/47501509/fysik/kompasser-och-magnet/index.html As the title states I want to make the compasses wiggle a bit like a compass would do naturally. What...
32. ### Direction of Compass Needle near a Solenoid

A compass is placed near a solenoid. It is closer to the North pole generated by the coil. The magnetic north is 90 deg relative to the compass and the solenoid. The strength of the solenoid is equal to the strength of the magnetic north. In which direction will the compass needle point?
33. ### Compass deflection by overhead transmission lines

Problem Description: A hiker is reading a compass under an overhead transmission line that is 5.1m above the ground and carries a current of 807A in a horizontal direction from North to South. Assume the Earth's field is of the order 0.5*10^-4T. A) Determine the magnitude of the field produced...
34. ### Altitude where Earth's magnetic field will no longer affect a compass

Hi, The Earth's magnetic field at the surface is roughly 0.5 Gauss or 0.05 mT. If the Earth's field strength diminishes in proportion to the inverse square of the distance, surely the field is going to be negligible at 10,000m altitude. Yet as far as I am aware it will still have an effect...
35. ### Flipping the polarity of a compass needle. Why does this work?

Awhile back I had been messing around with batteries, copper wiring, compasses and small neodymium magnets; during this time I figured out how to flip the polarity of a compass needle. The most reliable way was to hold the two magnets above the compass needle and force, as best I could, the two...
36. ### Putting a Compass in a Magnetic Field

Homework Statement If you put a compass in a magnetic field, the compass will... a) seek electrical charge concentrations. b) line up in a direction perpendicular to the magnetic field lines. c) swing randomly. d) line up in a direction parallel to the magnetic field lines. Which one is it...
37. ### News Where are you on the political compass this election?

http://www.politicalcompass.org/testI guess I'm not terribly surprised by my results; I'm registered libertarian, but kind of distanced myself from political parties since joining the circus... er, I mean academia: http://www.politicalcompass.org/facebook/pcgraphpng.php?ec=-6.12&soc=-4.21
38. ### My New Compass Won't Point North - What's Wrong?

I bought a compass today. I tested it at the store, multiple times, spinning all which ways. It would always immediately spin itself around to accurately point north.. It is one of those ball compasses like what's on the back of a survival knife. As soon as I got home it stopped pointing...
39. ### Using compass, construct 1 deg arc on a circle, if 19 deg arc of this circle is given

Exercise #27 from a textbook called Kiselev's Geometry / Book I. Planimetry: Using only compass, construct a 1 degree arc on a circle, if a 19 degree arc of this circle is given.Please, check my reasoning on this one. I just want to make sure that I'm getting it right. My solution: Using a...
40. ### Prove the impossibility of construction with ruler and compass the numbers:

Homework Statement ∛4 ∛5 ∛3 and ∛a Homework Equations The Attempt at a Solution I have started with the problem but i feel like I'm off track. I'll upload a pic of the work so far.
41. ### Could a new type of compass be created using a rotating permanent magnet?

Hello everyone. As a youngster I was asked to float a sewing needle on top of a full glass of water after I had magnetised it with a permanent magnet. The glass was so full the water was convex, slowly edging the point of the need toward the center of the glass. Noticing the capillary action...
42. ### Is Earth's Magnetic Field Affecting My Homemade Compass?

I've made a possible compass? I've fashioned a rotating permanent magnet rotor with four poles, like poles are opposite to each other. I made this to take advantage of the gyroscopic effect that would be realized at various rpms. The rotor is being pulsed by a DC pulse-coil to start and aid in...
43. ### Why Does the Compass Turn Right? Solve the Mystery!

Homework Statement Why does the compass turn right when a magnetic field other than the Earth is applied? This has been bugging me for a while, does anyone know the answer to this question? Thanks a lot :p Homework Equations None The Attempt at a Solution None
44. ### Exploring the Limits of Ruler and Compass Constructions in Abstract Algebra

Hi, I know next to nothing about abstract algebra (had one intro-class years ago), so sorry if this is a dumb question. I was browsing through "A book on abstract algebra" by Pinter and had a thought. In the chapter called "ruler and compass" (chapter 30) he talks about how abstract algebra...
45. ### Compass and the direction of a magnetic field

According to my physics textbook, one can find out the direction of a magnetic field by a small magnet. The magnet will line itself with the magnetic field with the north pole of the compass pointing in the direction of the field. http://dl.dropbox.com/u/345710/magnet%26compass.jpg...
46. ### Compass with stronger magnetic?

If compass on is not heading to south or north, the stronger magnetic will help it quicker return to the position?
47. ### Torque experienced by compass needle

The torque experienced by the compass needle is m X B , m being the magnetic moment of the compass/magnet and B being the Earth's magnetic field. The magnetic moment is along the axis pointing from South to North and the magnetic field will depend on where the compass is on the surface of the...
48. ### Compass Dip Error and Acceleration Compensation in Aircraft Navigation

When an aircraft heading east/west accelerates, it shows false northerly direction, similary on deacceleration shows southerly. I know the magnet in the aircraft, dip (not at the equator) bcoz it tries to align with the magnetic lines. To avoid this, the magnet needle is pivoted to a float...
49. ### Interpreting magnetic compass pitch and roll

Hello all, I have a PNI TCM2 electronic compass module, which has a 3-axis magnetometer and a 2-axis tiltmeter (manual: http://www.mil.ufl.edu/projects/gnuman/spec_sheets/tcm2_man.pdf" ), and provides heading with tilt compensation. The module also provides "pitch" and "roll" measurements...
50. ### Magnet - right hand rule - direction of compass North

Homework Statement A length of wire extends upward through a piece of cardboard, bends around, forming a loop, and extends back down through the cardboard. All that is visible above the surface of the cardboard is this loop of wire. From your perspective, you are looking downward on the piece...