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NEET UG PHYSICS MCQ: MAGNETISM AND MATTER

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Application +4 | -1

The magnetic needle of an oscillation magnetometer makes 10 oscillations per min under the action of earth’s magnetic field alone. When a bar magnet is placed at some distance along the axis of the needle, it makes 14 oscillations per min. If the bar magnet is turned so that its poles interchange their positions, then the new frequency of oscillation of the needle is

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Correct option: B

2

\mathrm{vibs}

-

{\mathrm{m}^{ - 1}}

Option B (2

\mathrm{vibs}

-

{\mathrm{m}^{ - 1}}

) is correct because it involves calculating the resultant magnetic field and then the frequency after the magnet's poles are interchanged.

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Assertion: If a unit north pole rotates around a current carrying wire then work has to be done.
Reason: Magnetic field produced by current is always non - conservative in nature. The magnetic length of a bar magnet is 15 cm then its geometric length is If area vector

\vec A = 2\vec i - 3\vec j + 6\vec k\,{m^2}

flux density vector

\vec B = - 3\vec i + \vec j + 2\vec k\,\left( {Wb/{m^2}} \right)

. Then magnetic flux linked with the coil is [Wb] The area of hysteresis loop of a material is equivalent to

250\;joule

10\;kg

material is magnetized by an alternating field of

50\;Hz

then energy lost in one hour will be (density of material is

7.5\;gm/c{m^3}

) A bar magnet of moment

M

is placed in the magnetic field

B

. The torque acting on the magnet is Assertion(A): Earth's magnetic field inside a closed iron box is less as compared to the out side.

Reason(R): The magnetic permeability of iron is low.