Question

A short bar magnet is placed in the magnetic meridian of the earth with north pole pointing north. Neutral points are found at a distance of $$30\,cm$$  from the magnet on the East-West line, drawn through the middle point of the magnet. The magnetic moment of the magnet in $$A{m^2}$$  is close to: (Given $$\frac{{{\mu _0}}}{{4\pi }} = {10^{ - 7}}$$   in $$SI$$  units and $${B_H} = $$  Horizontal component of earth’s magnetic field $$ = 3.6 \times {10^{ - 5}}tesla$$   )

A. 14.6
B. 19.4
C. 9.7  
D. 4.9
Answer :   9.7
Solution :
$$\eqalign{ & {\text{Here,}}\,\,r = 30\,cm = 0.3\,cm \cr & {\text{we}}\,{\text{know}}\,\frac{{{\mu _0}M}}{{4\pi {r^3}}} = {B_H} = 3.6 \times {10^{ - 5}} \cr & \Rightarrow M = \frac{{3.6 \times {{10}^{ - 5}}}}{{{{10}^{ - 7}}}}{\left( {0.3} \right)^3} = 9.7\,A{m^2} \cr} $$

Releted MCQ Question on
Electrostatics and Magnetism >> Magnetic Materials

Releted Question 1

Curie temperature is the temperature above which

A. a ferromagnetic material becomes paramagnetic
B. a paramagnetic material becomes diamagnetic
C. a ferromagnetic material becomes diamagnetic
D. a paramagnetic material becomes ferromagnetic
View Answer
Releted Question 2

The materials suitable for making electromagnets should have

A. high retentivity and low coercivity
B. low retentivity and low coercivity
C. high retentivity and high coercivity
D. low retentivity and high coercivity
View Answer
Releted Question 3

Needles $${N_1},{N_2}$$  and $${N_3}$$ are made of a ferromagnetic, a paramagnetic and a diamagnetic substance respectively. A magnet when brought close to them will

A. attract $${N_1}$$ and $${N_2}$$ strongly but repel $${N_3}$$
B. attract $${N_1}$$ strongly, $${N_2}$$ weakly and repel $${N_3}$$ weakly
C. attract $${N_1}$$ strongly, but repel $${N_2}$$ and $${N_3}$$ weakly
D. attract all three of them
View Answer
Releted Question 4

Relative permittivity and permeability of a material $${\varepsilon _r}$$ and $${\mu _r},$$ respectively. Which of the following values of these quantities are allowed for a diamagnetic material?

A. $${\varepsilon _r} = 0.5,{\mu _r} = 1.5$$
B. $${\varepsilon _r} = 1.5,{\mu _r} = 0.5$$
C. $${\varepsilon _r} = 0.5,{\mu _r} = 0.5$$
D. $${\varepsilon _r} = 1.5,{\mu _r} = 1.5$$
View Answer

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