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NEET UG PHYSICS MCQ: MAGNETISM AND MATTER

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The magnetic length of a bar magnet is 15 cm then its geometric length is

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Correct option: A

18 cm

Option A is correct because the geometric length is approximately 6/5 times the magnetic length for a bar magnet, resulting in 18 cm.

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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. 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. Force between two identical short bar magnets whose centers are

r

metre apart is 8.1 N, when their axes are along the same line. If separation is increased to 3

r

and the axis are rearranged perpendicularly, the force between them would become