# Magnetic Moment

## Trending Questions

**Q.**

What are coercivity and retentivity?

**Q.**An iron rod of length L and magnetic moment M is bent in the form of a semicircle. Now its magnetic moment will be

- 2Mπ
- Mπ
- M
- Mπ

**Q.**

An electric dipole with dipole moment P0√2(^i+^j) is held fixed at the origin O in the presence of an uniform electric field of magnitude E0. If the potential is constant on a circle of radius R centered at the origin as shown in the figure, then the correct statement (s) is/are : (∈0 is permittivity of free space. R >> dipole size)

The magnitude of total electric field on any two points of the circle will be same.

Total electric field at point A is →EA=√2E0(^i+^j)

R=(P04πε0E0)1/3

Total electric field at point B is →EB=0

**Q.**

**Statement I:**The ferromagnetic property depends on temperature. At high temperature, ferromagnet becomes paramagnet.

**Statement II:**At high temperature, the domain wall area of a ferromagnetic substance increases.

In the light of the above statements, choose the most appropriate answer from the options given below :

**Statement I**is false, but**Statement II**is true.- Both
**Statement I**and**Statement II**are true. **Statement I**is true, but**Statement II**is false.- Both
**Statement I**and**Statement II**are false.

**Q.**A circular coil of radius ‘r’ carries a current I. At what distance from centre on its axis the magnetic field is 127th of its value at the centre?

- 2√2r
- √3r
- 2√3r
- √5r

**Q.**

A non conducting disc of radius R is rotating about an axis passing through its centre and perpendicular to its plane with an angular velocity ω. Charge q is uniformly distributed over its surface. The magnetic moment of the disc is

14qωR2

12qωR

qωR

12qωR2

**Q.**The electric potential due to dipole at a general point which is at distance r from center of the dipole is

- V=k(→p⋅→r)r3
- V=k(→p⋅→r)r2
- V=k(→p⋅→r)r
- V=k(→p⋅→r)r4

**Q.**The effective length of a magnet is 31.4 cm and its pole strength is 0.5 Am. The magnetic moment, if it is bent in the form of a semicircle will be

- 0.01 Am2
- 0.2 Am2
- 0.1 Am2
- 1.2 Am2

**Q.**A positively charged particle having charge q and mass m moving with velocity v0^i enters a region in which magnetic field →B=−B0^k exists. The magnetic field region extends from x=0 to x=d. Then the time spent by the particle in magnetic field if d is equal to 1.5mvqB

- π mqB
- 2π mqB
- 2π m3qB
- π m4qB

**Q.**A point charge of 0.1 C is placed on the circumference of a non-conducting ring of radius 1 m which is rotating with a constant angular acceleration of 1 rad/sec2. If ring starts it's motion at t=0, the magnetic field at the centre of the ring at t=10 sec is 10−x. Then x is

**Q.**If a proton enters a region of uniform magnetic field with velocity v in a direction perpendicular to the magnetic field, then the time period of revolution is T. If proton enters with velocity 2v, the time period will be

- T
- 2T
- 3T
- 4T

**Q.**Two short bar magnets each of magnetic moment M are placed as shown in the figure. The magnetic field at the point P will be

- μ04π2√2Md3 towards right
- μ04π2√2Md3 towards left
- μ04π2Md3 towards left
- μ04π2Md3 towards right

**Q.**A bar magnet of magnetic moment 3.0 A−m2 is placed in a uniform magnetic induction field of 2×10−5 T. If each pole of the magnet experiences a force of 6×104 N, the length of the magnet is

- 0.5 m
- 0.3 m
- 0.2 m
- 0.1 m

**Q.**A square loop OABCO of side length l carries a current i. It is placed as shown in the figure. The magnetic moment of the loop will be :

- il22(^i−√3 ^k)
- il2(^j−√2 ^i)
- il25(^j−√5 ^i)
- il22(^j+√3 ^i)

**Q.**A long magnetic needle of length 2L, magnetic moment M and pole strength m units is broken into two pieces at the middle. The magnetic moment and pole strength of each piece will be

- M, m2

- M2, m

- M, m
- M2, m2

**Q.**A rod of length l rotates with a uniform angular velocity ω about its perpendicular bisector. A uniform magnetic field B exists parallel to the axis of rotation. The potential difference between the two ends of the rod is

- Zero
- 12Blω2
- Blω2
- 2Blω2

**Q.**

The combination of two bar magnets makes 10 oscillations per second in an oscillation magnetometer when like poles are tied together and 2 oscillation per second when unlike poles are tied together. Find the ratio of the magnetic moments of the magnets. Neglect any induced magnetism.

**Q.**A rod OPQ is rotating with angular speed ω about point O as shown in the figure. A uniform inward magnetic field B exists perpendicular to the plane of the rod. Potential difference between points P and Q of the rod is -

- Bωl22
- Bωl2
- Zero
- Bωl28

**Q.**when 4 bar magnets of moments M, 2M, 3M, 4M are arranged to form a square with unlike poles at each corner then resul†an t magnetic moment is

**Q.**A particle moving with velocity v having specific charge (qm) enters a region of magnetic field B having width d=3mv5qB at angle 53o to the boundary of magnetic field. Find the angle θ in the shown figure.

- 37∘
- 60∘
- 90∘
- None

**Q.**A short bar magnet is placed with its north pole pointing north. The neutral point is 10 cm away from the cemtre of the magnet.If B_H=0.4 G, calculate the magnetic moment of the magn

**Q.**

Considering that ${\u2206}_{\xb0}>\mathrm{P}$, the magnetic moment (in BM) of ${\left[\mathrm{Ru}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}\right]}^{+2}$ would be

**Q.**A bar magnet of length l and magnetic dipole moment M is bent in the form of an arc as shown in figure. The new magnetic dipole moment will be

- 2πM
- Mπ
- M
- 3πM

**Q.**The magnetic moment of a magnet of length 10 cm and pole strength 4.0 Am will be

- 1.6 Am2
- 0.4 Am2
- 20 Am2
- 8.0 Am2

**Q.**

A long bar magnet has a pole strength of 10 Am. Find the magnetic field at a point on the axis of the magnet distance of 5 cm from the north pole of the magnet.

**Q.**A Charged sphere of mass m and charge q starts sliding from rest on a vertical fixed circular track of radius R from the position as shown in figure. There exists a constant magnetic field in horizontal direction as shown in figure. The maximum force exerted by track on the sphere is:

- 3mg+qB√2gR
- mg+3qB√gR
- 2mg+qB√gR
- 2mg+3qB√2gR

**Q.**

Figure shows some of the equipotential surfaces of the magnetic scalar potential. Find the magnetic field B at a point in the region.

**Q.**Force between two unit pole strength placed at a distance of one metre is

- 10−74πN

- 10−7N

- 4π×10−7N
- 1 N

**Q.**As shown in the figure, a magnet is brought towards a fixed coil. Due to this, the induced emf, current and the charge are E, I and Q respectively. If the speed of the magnet is doubled, then which of the following statements is wrong?

- E increases.
- I increases.
- Q increases.
- None of the above

**Q.**

At ${45}^{\xb0}$ of the magnetic meridian angle of dip is $30\xb0$ then find the angle of dip in a vertical plane at $45\xb0$ ?

${\mathrm{tan}}^{-1}\left(\frac{1}{\sqrt{6}}\right)$

${\mathrm{tan}}^{-1}\left(\frac{1}{\sqrt{2}}\right)$

${\mathrm{tan}}^{-1}\left(\frac{1}{\sqrt{4}}\right)$

${\mathrm{tan}}^{-1}\left(\frac{1}{\sqrt{3}}\right)$