$A$ long straight horizontal cable carries a current of $2.5\;A$ in the direction $10^{\circ}$ south of west to $10^{\circ}$ north of east. The magnetic meridian of the place happens to be $10^{\circ}$ west of the geographic meridian. The earth's magnetic field at the location is $0.33\;G,$ and the angle of dip is zero. Locate the line of neutral points (ignore the thickness of the cable)? (At neutral points,magnetic field due to a current-carrying cable is equal and opposite to the horizontal component of earth's magnetic field.)
(N/A) Current in the wire,$I = 2.5 \; A$.
Angle of dip at the given location on Earth,$\delta = 0^{\circ}$.
Earth's magnetic field,$H = 0.33 \; G = 0.33 \times 10^{-4} \; T$.
The horizontal component of Earth's magnetic field is given by $H_{H} = H \cos \delta = 0.33 \times 10^{-4} \times \cos 0^{\circ} = 0.33 \times 10^{-4} \; T$.
The magnetic field $B$ at a distance $R$ from a long straight wire is $B = \frac{\mu_{0} I}{2 \pi R}$.
At neutral points,the magnetic field due to the wire must be equal and opposite to the horizontal component of Earth's magnetic field,so $B = H_{H}$.
Substituting the values: $0.33 \times 10^{-4} = \frac{4 \pi \times 10^{-7} \times 2.5}{2 \pi \times R}$.
Solving for $R$: $R = \frac{2 \times 10^{-7} \times 2.5}{0.33 \times 10^{-4}} = \frac{5 \times 10^{-7}}{0.33 \times 10^{-4}} \approx 1.515 \times 10^{-2} \; m = 1.51 \; cm$.
Thus,the neutral points lie on a straight line parallel to the cable at a perpendicular distance of $1.51 \; cm$ above the cable.
Angle of dip at the given location on Earth,$\delta = 0^{\circ}$.
Earth's magnetic field,$H = 0.33 \; G = 0.33 \times 10^{-4} \; T$.
The horizontal component of Earth's magnetic field is given by $H_{H} = H \cos \delta = 0.33 \times 10^{-4} \times \cos 0^{\circ} = 0.33 \times 10^{-4} \; T$.
The magnetic field $B$ at a distance $R$ from a long straight wire is $B = \frac{\mu_{0} I}{2 \pi R}$.
At neutral points,the magnetic field due to the wire must be equal and opposite to the horizontal component of Earth's magnetic field,so $B = H_{H}$.
Substituting the values: $0.33 \times 10^{-4} = \frac{4 \pi \times 10^{-7} \times 2.5}{2 \pi \times R}$.
Solving for $R$: $R = \frac{2 \times 10^{-7} \times 2.5}{0.33 \times 10^{-4}} = \frac{5 \times 10^{-7}}{0.33 \times 10^{-4}} \approx 1.515 \times 10^{-2} \; m = 1.51 \; cm$.
Thus,the neutral points lie on a straight line parallel to the cable at a perpendicular distance of $1.51 \; cm$ above the cable.
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Similar Questions
At an angle of $30^{\circ}$ to the magnetic meridian,the apparent dip is $45^{\circ}$. Find the true dip.
Which of the following relations is correct in the context of Earth's magnetism?
Medium
View SolutionAssume the dipole model for Earth's magnetic field $B$,which is given by:
$B_v = \text{vertical component of magnetic field} = \frac{\mu_0}{4\pi} \frac{2m \cos \theta}{r^3}$
$B_H = \text{horizontal component of magnetic field} = \frac{\mu_0}{4\pi} \frac{m \sin \theta}{r^3}$
where $\theta = 90^\circ - \text{latitude}$ as measured from the magnetic equator.
$(a)$ Find the loci of points for which the dip angle is zero.
$B_v = \text{vertical component of magnetic field} = \frac{\mu_0}{4\pi} \frac{2m \cos \theta}{r^3}$
$B_H = \text{horizontal component of magnetic field} = \frac{\mu_0}{4\pi} \frac{m \sin \theta}{r^3}$
where $\theta = 90^\circ - \text{latitude}$ as measured from the magnetic equator.
$(a)$ Find the loci of points for which the dip angle is zero.
Medium
View SolutionIf $\theta_1$ and $\theta_2$ are the apparent angles of dip observed in two vertical planes at right angles to each other,then the true angle of dip $\theta$ is given by:
MediumNEET 2017
View SolutionAnswer the following questions:
$(a)$ The earth's magnetic field varies from point to point in space. Does it also change with time? If so,on what time scale does it change appreciably?
$(b)$ The earth's core is known to contain iron. Yet geologists do not regard this as a source of the earth's magnetism. Why?
$(c)$ The charged currents in the outer conducting regions of the earth's core are thought to be responsible for earth's magnetism. What might be the 'battery' (i.e.,the source of energy) to sustain these currents?
$(d)$ The earth may have even reversed the direction of its field several times during its history of $4$ to $5$ billion years. How can geologists know about the earth's field in such distant past?
$(e)$ The earth's field departs from its dipole shape substantially at large distances (greater than about $30,000\; km$). What agencies may be responsible for this distortion?
$(f)$ Interstellar space has an extremely weak magnetic field of the order of $10^{-12}\; T$. Can such a weak field be of any significant consequence? Explain.
$(a)$ The earth's magnetic field varies from point to point in space. Does it also change with time? If so,on what time scale does it change appreciably?
$(b)$ The earth's core is known to contain iron. Yet geologists do not regard this as a source of the earth's magnetism. Why?
$(c)$ The charged currents in the outer conducting regions of the earth's core are thought to be responsible for earth's magnetism. What might be the 'battery' (i.e.,the source of energy) to sustain these currents?
$(d)$ The earth may have even reversed the direction of its field several times during its history of $4$ to $5$ billion years. How can geologists know about the earth's field in such distant past?
$(e)$ The earth's field departs from its dipole shape substantially at large distances (greater than about $30,000\; km$). What agencies may be responsible for this distortion?
$(f)$ Interstellar space has an extremely weak magnetic field of the order of $10^{-12}\; T$. Can such a weak field be of any significant consequence? Explain.
Medium
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