The Total solution for NCERT class 6-12
A compass needle free toturn in a horizontal plane is placed at the centre of circular coil of 30 turnsand┬аradius 12 cm. The coil is in a vertical plane making an angle of 45┬║with the magnetic meridian. When the current in the coil is 0.35 A, the needlepoints west to east.
(a)┬аDetermine thehorizontal component of the earthтАЩs magnetic field at the location.
(b)┬аThe current in thecoil is reversed, and the coil is rotated about its vertical axis by an angleof 90┬║ in the anticlockwise sense looking from above. Predict the direction ofthe needle. Take the magnetic declination at the places to be zero.
Number of turns in thecircular coil,┬аN┬а= 30
Radius of the circularcoil,┬аr┬а= 12 cm = 0.12 m
Current in thecoil,┬аI┬а= 0.35 A
Angle of dip,┬а╬┤┬а=45┬░
Where,
┬а= Permeability offree space = 4╧А┬а├Ч 10тИТ7┬аTm AтИТ1
= 5.49 ├Ч 10тИТ5┬аT
The compass needlepoints from West to East. Hence, the horizontal component of earthтАЩs magneticfield is given as:
BH┬а=┬аBsin┬а╬┤
= 5.49 ├Ч 10тИТ5┬аsin45┬░ = 3.88 ├Ч 10тИТ5┬аT = 0.388 G
(b)┬аWhen the current inthe coil is reversed and the coil is rotated about its vertical axis by anangle of 90 ┬║, the needle will reverse its original direction. In this case,the needle will point from East to West.