Question

The observed magnetic bearing of a line OE was found to be 185°. It was later discovered that station O had a local attraction of +1.5°. The true bearing of line OE, considering magnetic declination of 3.5° E shall be :
1. 180°
2. 187°
3. 190°
4. 193°

Answer 1

Correct Answer - Option 3 : 190°

Concept: 

Magnetic declination: At any place horizontal angel between true meridian and magnetic meridian is called magnetic declination

For Eastern declination,

α = β + θE 

or T.B = M.B + θE

For western declination,

α = β – θE or T.B = M.B – θW

Here,

α = true bearing or T.B

β = magnetic bearing or M.B

θE = eastern declination

θW = western declination

Calculation:

Given,

Magnetic Bearing of Line OE = 185°

Station O has local attraction = + 1.5°

So, Correct Magnetic Bearing of line OE = 185° + 1.5° = 186.5°

Declination = 3.5° E

∵ Declination is given in eastren direction, so

T.B = M.B + θ_E

T.B. = 186.5 + 3.5 = 190°