Physics Times 07.2019

At any point in the plane of axial and equatorial lines:
For a short magnet,
2
0
3

(3cos 1)M

B

4 d

  

 

 

  00 for axial line ;  ^900 for equatorial line

10. Earth’s Magnetic Field
    (I) Geographical Meridian: A vertical plane
    passing through the axis of rotation of the earth
    is called the geographical meridian.
    (II) Magnetic Meridian: A vertical plane passing
    through the axis of a freely suspended magnet
    is called the magnetic meridian.

V

H

B Bsin

tan

B B cos



  



Where =dip (or) inclination;  = declination

(III)Apparent dip

Relation between true dip ( ) and apprent

dips( & )  1 2

2 2 2

cot      1 cot 2 cot

11. Moving-Coil Galvanometer(MCG)
    The deflection torque is NiAB.

NiAB k  i k

NAB

  

i



• current sensitivity of the galvanometer

V



• voltage sensitivity of the galvanometer

(V = iR, R - is the resistance of the coil)

12. Vibration Magnetometer
    Vibration magnetometer is used to find the
    horizontal component of earth magnetic field at a
    point. Time period of oscillation and frequency of
    magnet is

2 and^11

2

H

H

T I n MB

MB T I

   



13. Tangent Law
    If we have two uniform magnetic fields B and BHat
    right angle to each other and if a bar magnet is
    placed in such a combination of fields.
    The magnet will be acted upon by two couples. It
    will set in direction , such that the couples balance
    each other.
    Deflection couple due to B



  mB NO mB l.2 cos

(2 ) cosml B MBcos

Resorting couple due to BH

  mB SO mB lH H.2 sin

(2m )B sinl H  MB sinH 

 When the magnet is in the equillibrium position,

B MB cos  MB sinH 

 B BHtan

At any point in the plane of axial and equatorial lines:

10. Earth’s Magnetic Field


11. Moving-Coil Galvanometer(MCG)
    12. Vibration Magnetometer
    13. Tangent Law
    14. Tangent Galvanometer (TG)
    

tanB B/ H (tangent law)

14. Tangent Galvanometer (TG)
    It is a moving magnet galvanometer used to
    measure current.
    The magnetic field at the centre is

0

2

ni

B

r



