Correct Answer - Option 1 : Metallic object
Explanation:
Local attraction:
- Local attraction is the phenomenon by which the magnetic needle is constantly prevented to point towards the magnetic north at a place.
- It is the attraction of the magnetic needle to a local magnetic field other than the earth's magnetic field.
- It can be caused by iron pipes, steel pipes, vehicles, etc.
- If the difference between fore bearing and back bearing is 1800 then both the end stations are considered to be free from local attraction
Important points about Local attraction:
1. If difference between fore bearing (FB) and Back bearing (BB) of a line is not equal to 1800 then either of station or both stations are affected by local attraction.
2. If difference between fore bearing (FB) and Back bearing (BB) of a line is equal to 1800 then there are two possibilities:
a) Both stations are free from local attraction.
b) Both stations are affected by same value of local attraction.