Magnetisation

Q. A magnetic compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It

1. will become rigid showing no movement
2. will stay in east - west direction only
3. will stay in north - south direction only
4. will stay in any position

Q.

What is a temporary magnet?

Q. The intrinsic carrier density at room temperature in $\text{Ge}$ is $2.37\times {10}^{19}{\text{m}}^{-3}$. If the mobility of electron and hole are $0.38{\text{m}}^2{\text{V}}^{-1}{\text{s}}^{-1}$ and $0.18{\text{m}}^2{\text{V}}^{-1}{\text{s}}^{-1}$, calculate the resistivity.

1. $0.671\Omega \text{-m}$
2. $0.471\Omega \text{-m}$
3. $0.271\Omega \text{-m}$
4. $0.871\Omega \text{-m}$

Q. A light beam is described by $E=800\sin \omega (t-\frac{x}{c})$. An electron is allowed to move normal to the propagation of light beam with a speed of $3\times {10}^7{\text{ms}}^{-1}$. What is the maximum magnetic force exerted on the electron ?

1. $1.28\times {10}^{-21}\text{N}$
2. $1.28\times {10}^{-18}\text{N}$
3. $12.8\times {10}^{-17}\text{N}$
4. $12.8\times {10}^{-18}\text{N}$

Q. A paramagnetic substance, in the form of a cube with sides $1\text{cm}$, has a magnetic dipole moment of $20\times {10}^{-6}\text{J/T}$, when a magnetic intensity of $60\times {10}^3\text{A/m}$ is applied. Its magnetic susceptibility is :

1. $3.3\times {10}^{-2}$
2. $4.3\times {10}^{-2}$
3. $2.3\times {10}^{-2}$
4. $3.3\times {10}^{-4}$

Q.

A jet plane is traveling towards the west at speed of $1800\mathrm{km}/\mathrm{h}$. What is the voltage difference developed between the ends of the wing having a span of $25\mathrm{m}$, if the Earths magnetic field at the location has a magnitude of $5\times {10}^{-4}\mathrm{T}$ and the dip angle is $30°$?

Q. For protecting a sensitive equipment from the external magnetic field, it should be

1. Placed inside an aluminium cane
2. Placed inside an iron cane

3. Wrapped with insulation around it when passing current through it

4. Surrounded with fine copper sheet

Q. The time period of a freely suspended magnet is 4 s. If it is broken in length into two equaetand one part is suspended in the same waits time period will be(2), 4 S(4) 0.25 s1) 2 s(3) 0.5 s

Q.

The magnetic field at a distance $\mathrm{r}$ from a long wire carrying current i is $0.4\mathrm{T}$. the magnetic field at a distance of $2\mathrm{r}$ is

Q. When 2 Amperes current is passed through a tangent galvanometer, it gives a deflection of ${30}^0$. For ${60}^0$ deflection, the current must be

1. 4 A
2. 6 A
3. 1 A
4. $2\sqrt{3}A$

Q. A long straight conductor, carrying a current I, is bent into the shape shown in the figure. The radius of the circular loop is r. The magnetic field at the centre of the loop is

1. $\frac{{\mu }_{0}i}{2r}[1-\frac{1}{\pi }]$ out of the page
   
2. $\frac{{\mu }_{0}i}{2r}[1+\frac{1}{\pi }]$ into the page
   
3. $\frac{{\mu }_{0}i}{2r}[1-\frac{1}{\pi }]$ into the page
   
4. $\frac{{\mu }_{0}i}{2r}[1+\frac{1}{\pi }]$ out of the page

Q. A wire loop PQRSP is constructed by joining two semi-circular coils of radius $r_1$ and $r_2$ respectively, as shown in the figure. If the current flowing in the loop is I, then the magnetic induction at the point O is:

1. $\frac{{\mu }_{0}I}{4}[\frac{1}{r_1}+\frac{1}{r_2}]$
   
2. $\frac{{\mu }_{0}I}{2}[\frac{1}{r_1}-\frac{1}{r_2}]$
   
3. $\frac{{\mu }_{0}I}{4}[\frac{1}{r_1}-\frac{1}{r_2}]$
   
4. $\frac{{\mu }_{0}I}{2}[\frac{1}{r_1}+\frac{1}{r_2}]$

Q. The average radius of a toroid, made out of a non-magnetic material, is $0.1\text{m}$ and it has $500$ turns. If it carries a $0.5\text{A}$ current, the intensity of magnetic field along its circular axis will be-

1. $\pi \times {10}^4\text{T}$
2. $2\pi \times {10}^4\text{T}$
3. $2.5\times {10}^{-4}\text{T}$
4. $5\times {10}^{-4}\text{T}$

Q.

Which of the following instruments is used to measure magnetic field

1. Thermometer

2. Pyrometer

3. Hygrometer

4. Flux meter

Q.

To shield an instrument from external magnetic field, it is placed inside a cabin made from

1. wood

2. ebonite

3. iron

4. any one of the above

Q. A delta rosette, as shown in figure, measures micro - strains as follows:
${ϵ}_A=-100\times {10}^{-6},{ϵ}_B=700\times {10}^{-6},{ϵ}_C=600\times {10}^{-6}$
What will be the principal strains, if modulus of elasticity is 200 GPa and Poisson's ratio is 0.3 ?

1. $260\times {10}^{-6}$ and $540\times {10}^{-6}$
2. $800\times {10}^{-6}$ and $-200\times {10}^{-6}$
3. $1020\times {10}^{-6}$ and $420\times {10}^{-6}$
4. None of these

Q. The magnetic induction in air at a distance d from an isolated point pole of strength m unit will be

1. $\frac{m}{d}$
   
2. $md$
   
3. $m{d}^2$
4. $\frac{m}{d^2}$
   

Q. A bar magnet of magnetic moment M is bent in the U shape such that all parts are of equal lengths. Then the new magnetic moment is

Q. The mqgnetic moment of a short bar magnet is 2Am2. The magnetic field t a point 1m away from it in a direction making an angle 60^° with its magmetic moment is 1. _/510-7 T 2. 10-7 T 3._/710-7T 4. 710-7T

Q. A bar magnet of magnetic dipole moment 10 Am^2 is in stable equilibrium the work done to rotate the magnet through 60 degree is l? The magnetic field is 0.2T

Q.

A $25cm$ long solenoid has a radius of $2cm$ and $500$ total number of turns. It carries a current of $15A$. If it is equivalent to a magnet of the same size and magnetization $\overrightarrow{M}$ (magnetic moment / vloume), then $\left|\overrightarrow{M}\right|$ is

1. $300A/m$

2. $30000A/m$

3. $30000\mathrm{\pi }A/m$

4. $3\mathrm{\pi }\mathrm{A}/\mathrm{m}$

Q. If a piece of metal was thought to be magnet, which one of the following observations would offer conclusive evidence

1. It attracts a known magnet
2. It repels a known magnet
3. Neither (a) nor (b)
4. It attracts a steel screw driver

Q. In what way is the behaviour of a diamagnetic material different from that of a paramagnetic one, when kept in an external magnetic field ?

Q.

What is self-demagnetisation?

Q.

The moment of a magnet $(15cm\times 2cm\times 1cm)$ is $1.2A{m}^2$. What is its intensity of magnetization?

Q. Magnetic field intensity is defined as

1. Number of lines of force crossing per unit volume
2. Magnetic moment per unit volume
3. Magnetic induction force acting on a unit magnetic pole
4. Number of lines of force crossing per unit area

Q. The radius of the coil of a tangent galvanometer, which has $10$ turns, is $0.1m.$ The current (in ampere) required to produce a deflection of ${60}^{\circ }$ is $(B_H=4\times {10}^{-5}T)$

Q. An example of a diamagnetic substance is

1. Copper
2. Aluminium
3. Iron
4. Nickel

Q. A tangent galvanometer has a coil of 25 turns and radius of 15 cm. The horizontal component of the earth's magnetic field is $3\times {10}^{-5}T$. The current required to produce a deflection of ${45}^0$ in it, is

1. 0.14 A
2. 0.29 A
3. $3.6\times {10}^{-5}A$
4. 1.2 A

Q. The error in measuring the current with a tangent galvanometer is minimum when the deflection is about

1. $0^0$
2. ${60}^0$
3. ${30}^0$
4. ${45}^0$