Earth magnetic elements angle of dip ka derivation​​

@ piyush 
the derivation is a little bit complex at your class 12^th level , so, u need to only remmeber the formula , nothing else , with diagram , the ques in exam will ask you about the direct application of the formula . 
u can use the formula 
B= u0M / 4 pie r square 
and can solve it and find it out , , 
and if u still req full derivation , then let me know i can explain that here . 
tan = 2 tan lambda 
after derivation u will get this relation . 
ALL THE BEST ..