Solenoid and Bar Magnet

Q.

Write any four properties of magnetic lines of force.

Q.

A long solenoid carrying a current produces a magnetic field $\mathrm{B}$ along its axis. If the current is doubled and the number of turns per cm is halved. the new value of the magnetic field is

1. $\frac{\mathrm{B}}{2}$

2. $\mathrm{B}$

3. $2\mathrm{B}$

4. $4\mathrm{B}$

Q.

A short bar magnet of magnetic moment $0.4J/T$ is placed in a uniform magnetic field of $0.16T$. The magnet is in stable equilibrium when the potential energy is

Q. If a magnet of pole strength m is divided into four parts such that the length and width of each part is half that of initial one, then the pole strength of each part will be

1. $\frac{m}{2}$
   
2. $\frac{m}{8}$
   
3. $4m$
4. $\frac{m}{4}$
   

Q. Two identical magnetic dipoles of magnetic moments $1.0A-m^2$ each, placed at a separation of 2m with their axis perpendicular to each other. The resultant magnetic field at a point midway between the dipoles is

1. $5\times {10}^{-7}T$
   
2. $\sqrt{5}\times {10}^{-7}T$
   
3. ${10}^{-7}T$
4. None of these

Q. Two identical thin bar magnets, each of length $l$ and pole strength $m$ are placed at right angles to each other with the north pole of one touching the south pole of the other. What is the resultant magnetic moment of the system?

1. $ml$
2. $\sqrt{2}ml$
3. $\sqrt{3}ml$
4. $\sqrt{5}ml$

Q. A magnet of magnetic moment M and pole strength m is divided in two equal parts, then magnetic moment of each part will be

1. M
2. $\frac{M}{2}$
3. $\frac{M}{4}$
4. 2M

Q. Two identical short bar magnets, each having magnetic moment of $10A{m}^2$, are arranged such that their axial lines are perpendicular to each other and their centres be along the same straight line in a horizontal plane. If the distance between their centres is 0.2 m, the resultant magnetic induction at a point midway between them is $({\mu }_0=4\pi \times {10}^{-7}H{m}^{-1})$

1. $\sqrt{2}\times {10}^{-7}$ Tesla
2. $\sqrt{5}\times {10}^{-7}$ Tesla
3. $\sqrt{2}\times {10}^{-3}$ Tesla
4. $\sqrt{5}\times {10}^{-3}$ Tesla

Q. A bar magnet has a length $8\text{cm}$. The magnetic field at a point at a distance $3\text{cm}$ from the centre in the broad- side (or equatorial) on position is found to be $4\times {10}^{-6}\text{T}$. Find the pole strength of the magnet.

1. $8\times {10}^{-2}\text{Am}$
2. $1.25\times {10}^{-2}\text{Am}$
3. $6.25\times {10}^{-2}\text{Am}$
4. $3\times {10}^{-2}\text{Am}$

Q. If a bar magnet of pole strength $m$ and magnetic moment $M$ is cut equally into $6$ parts parallel to its axis and again $5$ equal parts perpendicular to its axis, then the pole strength and magnetic moment of each piece respectively:

1. $m,\frac{M}{6}$
2. $6m,\frac{M}{5}$
3. $\frac{m}{6},\frac{M}{5}$
4. $\frac{m}{6},\frac{M}{30}$

Q. The ultimate individual unit of magnetism in any magnet is called

1. South pole
2. Dipole
3. Quadrupole
4. North pole

Q. A bar magnet of length 3 cm has points A and B along its axis at distances of 24 cm and 48 cm on the opposite sides. Ratio of magnetic fields at these points will be

1. $4$
2. $\frac{1}{2\sqrt{2}}$
3. 8
4. $3$

Q. A small bar magnet is placed with its north pole facing magnetic north pole of earth. The neutral points are located at distance $r$ from its centre. If the magent is rotated by 180${}^{\circ }$, netural point shall be obtained at distance

1. $2r$
2. $\sqrt{2}r$
3. $2^{\left(-\frac{1}{3}\right)}r$
4. $\frac{r}{2\sqrt{2}}$

Q. A short bar magnet has a magnetic moment of 0.48 J T–1. Give the direction and magnitude of the magnetic field produced by the magnetat a distance of 10 cm from the centre of the magnet on (a) the axis, (b) the equatorial lines (normal bisector) of the magnet.

Q.

A bar magnet has a length of 8 cm. The magnetic field at a point at a distance 3 cm from the centre in the broadside-on position is found to be 4 $\times {10}^{-6}$ T. Find the pole strength of the magnet.

Q. The distance of two points on the axis of a magnet from its centre is 10 cm and 20 cm respectively. The ratio of magnetic intensity at these points is 12.5 : 1. The length of the magnet will be

1. 5 cm
2. 25 cm
3. 10 cm
4. 20 cm

Q. Ratio of magnetic intensities for an axial point and a point on broad side-on position at equal distance d from the centre of magnet will be or The magnetic field at a distance d from a short bar magnet in longitudinal and transverse positions are in the ratio

1. 2 : 3

2. 3 : 2

3. 1 : 1
4. 2 : 1

Q. A small bar magnet has a magnetic moment $1.2A-m^2$. The magnetic field at a distance 0.1 m on its axis will be: $({\mu }_0=4\pi \times {10}^{-7}T-m/A)$

1. $1.2\times {10}^{-4}T$
2. $2.4\times {10}^{-4}T$
3. $2.4\times {10}^{4}T$
4. $1.2\times {10}^{4}T$

Q. Points A and B are situated along the extended axis of 2 cm long bar magnet at a distance x and 2x cm respectively. From the pole nearer to the points, the ratio of the magnetic field at A and B will be

1. 4 : 1 exactly
2. 4 : 1 approx
3. 8 : 1 exactly
4. 8 : 1 approx

Q. What happens to the force between magnetic poles when their pole strength and the distance between them are both doubled

1. Force decreases to half the previous value

2. Force increases to four times the previous value

3. Force increases to two times the previous value
4. No change

Q. Magnetic intensity for an axial point due to a short bar magnet of magnetic moment M is given by

1. $\frac{{\mu }_0}{4\pi }\times \frac{M}{d^3}$
   
2. $\frac{{\mu }_0}{4\pi }\times \frac{M}{d^2}$
   
3. $\frac{{\mu }_0}{2\pi }\times \frac{M}{d^2}$
4. $\frac{{\mu }_0}{2\pi }\times \frac{M}{d^3}$
   

Q. Two similar bar magnets P and Q, each of magnetic moment M, are taken, If P is cut along its axial line and Q is cut along its equatorial line, all the four pieces obtained have

1. Magnetic moment $\frac{M}{4}$
2. Magnetic moment $\frac{M}{2}$
3. Equal pole strength
4. Magnetic moment M

Q. The magnetic induction field strength at a distance of $0.3\text{m}$ on the axial line of a short bar magnet of moment $3.6{\text{Am}}^2$ is

1. $2.6\times {10}^{-5}\text{T}$
2. $9\times {10}^{-5}\text{T}$
3. $9\times {10}^{-4}\text{T}$
4. $4.5\times {10}^{-4}\text{T}$

Q. The magnetic lines of force inside a bar magnet

1. Are from south-pole to north-pole of the magnet
2. Are from north-pole to south-pole of the magnet
3. Do not exist
4. Depend upon the area of cross-section of the bar magnet

Q.

Consider a square loop of side $4\text{cm}$ is positioned in a uniform magnetic field of magnitude $0.5\text{T}$ so that the plane of the loop makes an angle of ${30}^{\circ }$ with the magnetic field. Calculate amount of flux passing through the square loop.

1. $2\times {10}^{-4}\text{weber}$
2. $4\times {10}^{-3}\text{weber}$
3. $4\times {10}^{-5}\text{weber}$
4. $4\times {10}^{-4}\text{weber}$

Q. A bar magnet of length $3\text{cm}$ has point $A$ and $B$ along its axis at distance of $24\text{cm}$ and $48\text{cm}$ on the opposite sides, as shown in the diagram. Ratio of magnetic fields at these points will be,

1. $8$
2. $\frac{1}{2\sqrt{2}}$
3. $3$
4. $4$

Q. Four magnets of equal length but magnetic moments $M,2M,3M$ and $4M$ respectively are arranged in the form of a square such that their unlike poles are in contact. Then the resultant magnetic moment of the system is-

1. $2M$
2. $2\sqrt{2}M$
3. $\sqrt{2}M$
4. $\sqrt{3}M$

Q.

A solenoid of the length $50cm$of the inner radius of $1cm$ and is made up of $500$ turns of copper wire for a current of $5A$ in it. What will be the magnitude of the magnetic field inside the solenoid?

Q. If the ratio of magnetic fields on the axial line of a long magnet at distances of $10\text{cm}$ and $20\text{cm}$ is $12.5:1$, then the length of the magnet will be

1. $\text{20 cm}$
2. $\text{40 cm}$
3. $\text{30 cm}$
4. $\text{10 cm}$

Q. What happens to the force between magnetic poles when their pole strength and the distance between them are both doubled

1. Force increases to two times the previous value
2. No change
3. Force decreases to half the previous value

4. Force increases to four times the previous value