General Navigation - Magnetism and Compasses Flashcards
What are true directions referenced to?
True directions are referenced to the meridians and the north pole.
How do most aircraft find their direction?
Most aircraft use compasses to find their direction, referencing the Earth’s magnetic pole.
Where does permanent magnetism occur?
Permanent magnetism occurs in iron and some of its alloys, and occasionally in other compounds.
How can temporary magnetism be induced?
Temporary magnetism can be induced by electrical currents in an electromagnet.
What is related to electricity and suspected to be part of a family of forces that shape space and time?
Magnetism is known to be related to electricity and suspected to be part of a family of forces that shape space and time.
Are all pieces of iron and steel magnetic?
No, not all pieces of iron and steel are magnetic. They can be magnetized and demagnetized if correct techniques are applied.
How can the molecular theory of magnetism be explained?
By thinking of the molecules of iron as individual magnets. In the unmagnetized state, the molecular magnets point in all directions. When the iron is magnetized, the molecules line up to create one large magnet.
What is meant by ‘saturated’ in the context of magnetism?
When iron attains its maximum magnetism, it is said to be saturated.
What is soft iron?
Soft iron is iron that becomes saturated easily and also loses its magnetism easily.
What is hard iron?
Hard iron is iron that is difficult to magnetize and keeps its magnetism.
How can molecular magnets be induced to line up?
By several methods, such as stroking a nail with a magnet, placing iron in a magnetic field, hammering the iron, or placing it inside a solenoid with a strong DC current passing through it.
How can iron be demagnetized?
By heating it to around 900°C, placing it in an oscillating magnetic field, or being hammered when positioned at right angles to a magnetic field.
How are magnetic fields represented?
By lines of force leaving one pole and going into the other. The poles are labeled north or red and south or blue.
What happens to soft iron placed in a magnetic field?
It will deflect the field lines and can leave an air gap where there is no field.
Where is the actual pole of a magnet?
The actual pole is not at the end of the magnet but some distance inside. Long thin magnets have their poles near the ends, while short fat magnets, like the Earth, have the pole further in. This is why compass needles point down into the Earth near the poles.
How can magnetic fields be represented?
By lines of force leaving one pole and going into the other, with poles labeled north (red) and south (blue).
What happens to soft iron placed in a magnetic field?
It deflects the field lines and can leave an air gap where there is no field.
Where is the actual pole of a magnet located?
Not at the end of the magnet but some distance inside.
How do long thin magnets and short fat magnets differ in pole location?
Long thin magnets have poles near the ends, while short fat magnets, like the Earth, have the pole further inside.
Why do compass needles point down into the Earth near the poles?
Because the Earth’s magnetic pole is further inside the Earth, similar to short fat magnets.
How does the Earth’s iron core behave?
Like a huge magnet with north and south poles.
Is the Earth’s magnetic pole coincident with the geographic pole?
No, it is not coincident with the geographic pole.
Which pole does the area referred to as the ‘north magnetic pole’ correspond to physically?
It corresponds to a south magnetic pole, the pole to which the north end of a magnet would point.
What is the confusion related to the Earth’s magnetic poles and colors?
The Earth’s north magnetic pole is actually the magnet’s south pole (colored blue), and the Earth’s south magnetic pole is the magnet’s north pole (colored red).
How do maps and charts refer to the Earth’s magnetic poles?
They refer to the ‘blue’ north magnetic pole and the ‘red’ south magnetic pole.
What happens when a magnet is lined up with the lines of force?
It does not line up with the true meridians and is not horizontal with respect to the Earth, except along the magnetic equator or aclinic line.
What is the angle between the true meridian and the magnetic meridian called?
It is called variation.
How does variation vary across the Earth?
Between 180° on a line joining the true and magnetic poles and zero where this line extends beyond the two poles.
What are lines joining points of equal variation on the Earth’s surface called?
Isogonals.
What is the line along which variation is zero called?
The agonic line
Where do the isogonals converge?
The isogonals converge at the magnetic poles and at the true poles.
How does the Earth’s magnetic pole move?
The Earth’s magnetic pole is slowly moving around the true pole, causing variation to change over time.
Why should maps and charts always be checked?
Maps and charts should always be checked to find the date at which the variation is correct and any necessary corrections should be applied.
What is variation?
Variation is the difference between the direction of the datums and the difference between all true directions and their corresponding magnetic directions at any point.
How is true direction measured?
True direction is based on the local meridian of longitude joining the true north and south poles.
How is magnetic direction measured?
Magnetic direction may be measured from the local magnetic meridian joining the magnetic north and south poles but following the flux line or lines of force of the Earth’s magnetic field.
How is variation measured and named?
Variation is measured in degrees and is named east or west according to whether magnetic north lies to the east or west of true north at that point.
How is true heading calculated?
Magnetic heading, plus or minus variation, equals true heading.
What is the rhyme to determine whether variation should be added or subtracted?
Variation east magnetic least, variation west magnetic best.
What is the difference between true and magnetic headings called?
Variation.
When a magnetic needle is influenced only by the Earth’s magnetic field, where does it point?
It points to magnetic north.
What happens if a compass is installed in an airplane?
The Earth’s magnetic field will be distorted by the metal and the electrical equipment around it.
What is the term for the direction indicated by a compass in an airplane?
Compass north.
What is the difference between magnetic north and compass north called?
Deviation.
