## Magnetic Declination and Dip – Class 12 | Chapter – 5 | Physics Short Notes Series PDF for NEET & JEE

Magnetic Declination and Dip: Magnetic declination and magnetic dip are two important concepts related to the Earth’s magnetism. Both magnetic declination and magnetic dip are affected by the Earth’s magnetic field, which is not static and can vary over time. The magnetic field has flipped polarity many times throughout the Earth’s history, with the north and south magnetic poles switching places, which can have significant effects on magnetic declination and dip.

## Magnetic Declination and Dip

Magnetic declination, also known as magnetic variation, is the angle between magnetic north (the direction that a compass needle points) and true north (the direction of the geographic North Pole) at a particular location on the Earth’s surface. Magnetic declination varies depending on the location on the Earth’s surface and can change over time. It is an important factor in navigation, as it must be taken into account when using a compass for direction-finding.

Magnetic dip, also known as inclination, is the angle between the horizontal plane and the direction of the Earth’s magnetic field at a particular location on the Earth’s surface. At the magnetic equator, the dip is zero, meaning the magnetic field is horizontal. At the magnetic poles, the dip is 90 degrees, meaning the magnetic field is vertical. Magnetic dip varies depending on the location on the Earth’s surface and can also change over time.

## How To Calculate Magnetic Declination and Dip

There are several ways to calculate the magnetic declination at a particular location on the Earth’s surface, including:

• Magnetic declination charts: These charts show the magnetic declination for various locations on the Earth’s surface. They are usually published by national surveying and mapping agencies and can be used to determine the magnetic declination for a specific location.
• Magnetic declination calculators: There are online calculators that use current and historical data to calculate the magnetic declination for a particular location.
• Compasses: A magnetic compass can be used to determine the magnetic declination by comparing the angle between magnetic north and true north. This method requires a known or estimated value for the true north at the location.
• Satellite-based navigation systems: Some satellite-based navigation systems, such as GPS, can provide information about magnetic declination for a particular location.
 T = M + V M = C + D T = C + V + D (which is a general equation relating compass and true bearings)

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 for westerly variation and deviation
• V > 0, D > 0 for easterly variation and deviation

Following is the way to calculate compass bearing from true bearing:

• True bearing – variation = magnetic bearing
• Magnetic bearing – deviation = compass bearing

Following is the way to calculate true bearing from compass bearing:

• Compass bearing + deviation = magnetic bearing
• Magnetic bearing + variation = true bearing

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