NEET UG PHYSICS MCQ: MAGNETISM AND MATTER

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Analyzing +4 | -1

Using a bar magnet

P

, a vibration magnetometer has time period

2seconds

. When a bar

Q

(identical to

P

in mass and size) is placed on top of

P

, the time period is unchanged. Which of the following statements is true

View answer and explanation

Correct option: B

Q

is a bar magnet identical to

P

, and its north pole is placed on top of

P'

s north pole

Option B (

Q

is a bar magnet identical to

P

, and its north pole is placed on top of

P

's north pole) is correct because the time period remains unchanged, implying the effective magnetic moment doubles, which only happens when identical magnets are aligned.

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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.