Magnetism And Matter

Q: A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. the energy required to rotate it by \$60^o\$ is \$W\$, Now the torque required to keep the magnet in this new position is.

Hint:-Use potential energy formula to calculate the energy required to rotate the magnet and hence calculate torque.Step 1: Calculate energy required to rotate magnet by \$60^{\circ}\$.Energy required or work done in moving from \$\theta=0^{\circ}\$ to \$\theta=60^{\circ}\$ is given by \$W=-mBcos 60^{\circ}-(- mBcos 0)=\dfrac{1}{2}mB\$Step 2: Calculate the torque required to keep the magnet in the new position.The torque acting on a bar magnet kept in a magnetic field \$\vec{B}\$ is given by \$\tau=\vec{m}\times \vec{B}=mBsin\theta\$\$\tau=mBsin60^{\circ}\$\$\tau=\dfrac{\sqrt3}{2}mB=\sqrt3W\$\$\textbf{Hence option C correct}\$

Q: A short bar magnet of magnetic moment \$0.4 J {T}^{-1}\$ is place in a uniform magnetic field of \$0.16 T\$. The magnet is stable equilibrium when the potential energy is

For stable equilibrium\$U = -MB\$ \$= -\left(0.4\right) \left(0.16\right)\$ \$= -0.064 J\$.

Q: A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from.

Here when electromagnet is connected to battery, emf source the magnetic field is produced which pushes rod upwards and so gravitational potential energy is stored.This stored energy will require work which will come from current source or battery which is connected to electromagnet.So option 2 is correct answer

Physics
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A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. the energy required to rotate it by $6 0^{o}$ is $W$ , Now the torque required to keep the magnet in this new position is.

\frac{2 W}{3}

\frac{W}{3}

3 W

\frac{3}{2} W

Medium

NEET

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A short bar magnet of magnetic moment $0.4 J T^{- 1}$ is place in a uniform magnetic field of $0.16 T$ . The magnet is stable equilibrium when the potential energy is

- 0.064 J

Zero

- 0.082 J

0.064

Medium

NEET

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A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from.

The lattice structure of the material of the rod

The current source

The induced electric field due to the changing magnetic field

The magnetic field

Medium

NEET

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Magnetism And Matter

Physics 4161 Views

A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. the energy required to rotate it by 60o is W, Now the torque required to keep the magnet in this new position is.

A short bar magnet of magnetic moment 0.4JT−1 is place in a uniform magnetic field of 0.16T. The magnet is stable equilibrium when the potential energy is

Physics
4161 Views

A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. the energy required to rotate it by $6 0^{o}$ is $W$ , Now the torque required to keep the magnet in this new position is.

A short bar magnet of magnetic moment $0.4 J T^{- 1}$ is place in a uniform magnetic field of $0.16 T$ . The magnet is stable equilibrium when the potential energy is