NEET UG PHYSICS MCQ: MAGNETISM AND MATTER

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A bar magnet is demagnetized by inserting it inside a solenoid of length 0.2m, 100 turns, and carrying a current of 5.2 A. The coercivity of the bar magnet is:

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Correct option: B

2600 A/m

Option B is correct. The coercivity is calculated using the formula

H = \frac{{NI}}{{L}}

, where N is the number of turns, I is the current, and L is the length of the solenoid.

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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

. When

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.