What is Magnetic Declination?
Magnetic declination can be defined as the angle on the horizontal plane between magnetic and true north. This isn't consistent and keeps on changing relying upon the situation upon the world's surface and time. The Greek letter δ is recognized as the magnetic declination symbol and is otherwise called magnetic variation.
The declination will be positive when the magnetic north is east of true north, and the declination will be negative when the magnetic north is west of true north. Different terms utilized are isogonic lines (when the lines along the declination are consistent) and agonic lines (when the lines along the declination are zero)
Intrigued to learn more ideas identified with the magnetic field, have a look at more ideas underneath:
Electromagnetic Induction
Magnetic Flux
Magnetic Field and Magnetic Field Lines
Magnetic Poles and Their Significance
There are three kinds of the north: True north, Grid north, and Magnetic north.
What is True North?
True north can be defined as the direction towards the true north or the geological North Pole along the earth's surface. It is otherwise called geodetic north and is not the same as the magnetic north which is the direction pointed by the compass and from the grid north which is toward the path along the grid lines towards the north.
What is Grid North?
Grid north can be defined as the direction which is in northwards along the grid lines on a map projection. This term is utilized for route and the deviation of the grid north from the true north is less.
What is Magnetic North?
Magnetic north can be defined as the direction which is pointed by the compass needle in light of the earth's magnetic field. The deviation between the true north and the magnetic north differs from one to another as the earth's magnetic poles are not fixed as for its axis.
Contrast Between Magnetic North and True North
Following is the table clarifying magnetic north versus true north:
Magnetic North: It is pointed by the compass needle in the north direction which is along the earth's magnetic field.
True North: It is the topographical north pointing towards the North Pole.
What is Magnetic Dip?
The magnetic dip can be defined as the edge by the earth's magnetic field lines made with the horizontal. It is otherwise called dip angle or magnetic inclination and was found by Georg Hartmann in the year 1544. At the point when the inclination is positive, it shows that the earth's magnetic lines are pointing downward in the northern half of the globe and when the inclination is negative it demonstrates that the earth's magnetic lines are facing upward in the southern side of the equator.
In the year 1581, Robert Norman found a dip circle which is a technique to estimate the dip angle. Different terms utilized are isoclinic lines (when the contour lines are equivalent at the earth's surface) and aclinic lines (when the locus of the points are having zero dips).
How to Calculate Magnetic Declination?
From the declination calculator: The declination calculator is a simple method to figure the declination of any location on the earth. By giving the year, scope, and longitude of a given area, the calculator gives the declination based on magnetic reference field models.
From a magnetic declination chart: A magnetic declination chart is a guide with the earth's magnetic fields accessible on it.
From a compass: There are three kinds of bearing, they are true, magnetic, and compass bearing. A compass can be utilized to figure the declination as it is one of the mistakes of the compass and the other is magnetic variation. These three are connected by:
T = M + V
M = C + D
T = C + V + D (which is a general condition relating compass and true direction)
Where,
C is the compass bearing
M is the magnetic bearing
T is the true bearing
V is the variation
D is the compass deviation
V < 0, D < 0: this represents westerly variation and deviation
V > 0, D > 0: this represents easterly variation and deviation
Following is the best approach to compute compass bearing from true bearing:
True bearing – variation = magnetic bearing
Magnetic bearing – deviation = compass bearing
Following is the best approach to compute true bearing from compass bearing:
Compass bearing + deviation = magnetic bearing
Magnetic bearing + variation = true bearing
Presently it turns out to be evident that when we check for north direction utilizing a compass, the needle is really pointing towards the earth's magnetic north and not the true north.
FAQs on Magnetic Declination
1. What is magnetic declination as per the CBSE Class 12 Physics syllabus?
Magnetic declination, also known as magnetic variation, is the angle between magnetic north (the direction a compass needle points) and true north (the direction along the Earth's axis of rotation towards the geographic North Pole) at any given location on the Earth's surface. It is one of the three magnetic elements of the Earth and is measured in degrees and minutes, east or west.
2. What is the fundamental difference between true north and magnetic north?
The key difference lies in their origin and location:
- True North is a fixed point on the globe, representing the Geographic North Pole, which is the northern end of the Earth's rotational axis. All longitude lines converge at this point.
- Magnetic North is the point towards which a compass needle aligns itself with the Earth's magnetic field lines. This point wanders over time due to changes in the Earth's molten outer core. Because of this, the magnetic north pole is not at the same location as the geographic North Pole.
3. How does magnetic declination differ from magnetic dip (or inclination)?
Magnetic declination and magnetic dip are both crucial elements of Earth's magnetism but measure different things:
- Magnetic Declination is a horizontal angle. It measures the deviation of a compass needle from the true north-south line on a horizontal plane (like a map).
- Magnetic Dip (or Inclination) is a vertical angle. It measures the angle that the Earth's magnetic field line makes with the horizontal surface. A dip needle, which can pivot vertically, is used to measure it. The dip is 0° at the magnetic equator and 90° at the magnetic poles.
4. Why is understanding magnetic declination important for real-world applications like navigation and surveying?
Magnetic declination is critical for accuracy in several fields. In navigation (maritime and aviation), a pilot or sailor must correct their compass bearing for declination to plot a course relative to true north on a map. Ignoring it can lead to significant navigational errors over long distances. In surveying, property boundaries and construction projects are defined by true bearings. Surveyors must precisely account for local declination to ensure their measurements are accurate and legally sound.
5. What are isogonic and agonic lines in the context of magnetic declination?
Isogonic and agonic lines are used on magnetic charts to map out declination:
- An isogonic line is an imaginary line connecting all points on the Earth's surface that have the same magnetic declination.
- An agonic line is a special isogonic line that connects points where the magnetic declination is zero. Along the agonic line, a compass needle points directly to true north.
6. Why is magnetic declination not a constant value for a given location?
Magnetic declination is not constant due to a phenomenon called secular variation. The Earth's magnetic field is generated by the movement of molten iron in its outer core. As this flow is dynamic and constantly changing, the position of the magnetic poles wanders over time. This wandering causes the Earth's magnetic field, and thus the magnetic declination at any specific point, to slowly and continuously change from year to year.
7. What does a positive (East) or negative (West) declination signify?
The sign of the declination indicates the direction of magnetic north relative to true north:
- Positive or East Declination means that magnetic north is to the east of true north. To find true north from a compass reading, you would subtract the declination value.
- Negative or West Declination means that magnetic north is to the west of true north. To find true north from a compass reading, you would add the declination value.
8. How can a student determine the magnetic declination for a specific location for the year 2025-26?
To find an accurate, up-to-date value for magnetic declination, a student can use reliable scientific models. The most common method is to use online calculators provided by geophysical organizations like the US National Oceanic and Atmospheric Administration (NOAA). These calculators use the World Magnetic Model (WMM), which provides the most precise values for any location and is updated every five years to account for secular variation. Using a printed map is less accurate as the data can become outdated.
