Untitled Document

Question Bank No: 2

1. If current is passed through a spring then it

a)		compress
b)		expand
c)		oscillate
d)		rotate

2. Weber/ $m^{2}$ is the unit of

a)		magnetic induction
b)		magnetic field intensity
c)		magnetic flux density
d)		All of these

3. Two straight long current carrying conductors LOM and NOK carrying current $I_{1}$ and $I_{2}$ respectively are perpendicular to each other. The magnetic field intensity produced at point P at a distance 'a' from 'O' in the direction perpendicular to the plane LMNK is

a)		$\frac{μ_{0}}{2 π a} {(I_{1}^{2} + I_{2}^{2})}^{1 / 2}$
b)		$\frac{μ_{0}}{2 π a} {(I_{1} + I_{2})}^{1 / 2}$
c)		$\frac{μ_{0}}{2 π a} {(I_{1} - I_{2})}^{1 / 2}$
d)		$\frac{μ_{0}}{2 π a} {(\frac{I_{1} + I_{2}}{I_{1} + I_{2}})}^{1 / 2}$

4. A wire of length l carrying current I is first bent to a circular loop of one turn. The same wire is now wound more sharply to three turns of smaller circular loops. The magnetic field produced at the center with same current I is

a)		Unaltered
b)		Nine times of the first value
c)		One third of its first value
d)		Three times of its first value

5. On connecting a battery to the two cornersof a diogonal of a square conducting frame of side 'a', the magnitude of the magnetic field at centre will be

a)		Zero
b)		$\frac{μ_{0}}{π a}$
c)		$\frac{2 μ_{0}}{π a}$
d)		$\frac{4 μ_{0} I}{π a}$

6. A current carrying wire is stretched horizontal and carrying current along west to east. The direction of magnetic field 1m above the wire will be

a)		West to east
b)		East to west
c)		North to south
d)		South to north

7. Two protons move parallel to each other with an equal velocity 300 km $s^{- 1}$ . If the two protons are moving at a perpendicular seperation of $r_{m}$ then force of magnetic interaction ${\vec{F}}_{m}$ is given by

a)		$\frac{μ_{0}}{4 π} \frac{e^{2}}{r^{2}} \times ({- v}^{2} \vec{r})$
b)		$\frac{μ_{0}}{4 π} \frac{e^{2}}{r^{2}} \times (v^{2} \vec{r})$
c)		$\frac{μ_{0}}{4 π} \frac{e^{2}}{r^{3}} \times ({- v}^{2} \vec{r})$
d)		$\frac{μ_{0}}{4 π} \frac{e^{2}}{r^{3}} \times (v^{2})$

8. If the torsional constant of the suspension of two moving coil galvanometers have same value and rest of the parameter are as under
Meter A : N = 30, A = ${1.5 \times 10}^{- 3} m^{2}$
B = 0.25 T, R = 20 $Ω$
Meter B : N = 35, A = ${2 \times 10}^{- 3} m^{2}$
B = 0.257, R = 30 $Ω$
then $\frac{(Current sensitivity) A}{(Current sensitivity) B}$

a)		$\frac{28}{27}$
b)		$\frac{9}{28}$
c)		$\frac{27}{28}$
d)		$\frac{9}{14}$

9. Two identical coils placed with their planes at light angle such that their centres coincides with each other. If the same current flows through the two wires then what is the ratio of magnitude of the resultant magnetic field at the centre and the field due to one coil along its axis

a)		2 : 1
b)		1 : $\sqrt{2}$
c)		$\sqrt{2}$ : 1
d)		1 : 1

10. A long copper tube of inner radius R carries a current I. The magnetic field B inside the tube is

a)		$\frac{μ_{0} I}{2 π R}$
b)		$\frac{μ_{0} I}{2 R}$
c)		Zero
d)		$\frac{μ_{0} I}{4 π R}$

11. An electron is revolving around a proton in a circular path of diameter 1 $\overset{\circ}{A}$ . It produces a magnetic field of 14 T at the proton. Then angular speed of the electron is

a)		${8.8 \times 10}^{6} rad s^{- 1}$
b)		${4.4 \times 10}^{16} rad s^{- 1}$
c)		${1.1 \times 10}^{16} rad s^{- 1}$
d)		${2.2 \times 10}^{16} rad s^{- 1}$

12. Two parallel wires in free space are 10 cm apart and each carries a current of 10 A in the same direction. The force experienced per unit length of each will

a)		${2 \times 10}^{- 4} N$ attractive
b)		${2 \times 10}^{- 4} N$ repulsive
c)		${2 \times 10}^{- 7} N$ attractive
d)		${2 \times 10}^{- 7} N$ repulsive

13. A long straight wire along z-axis carries a current I in the -ve z-direction. The magnetic field vector $\vec{B}$ at a point having co-ordinates (x, y) in the z = 0 plane is

a)		$\frac{μ_{0}}{2 π} \frac{I (y \hat{i} - x \hat{j})}{x^{2} + y^{2}}$
b)		$\frac{μ_{0}}{2 π} \frac{I (x \hat{i} + y \hat{j})}{x^{2} + y^{2}}$
c)		$\frac{μ_{0}}{2 π} \frac{I (x \hat{j} - y \hat{i})}{x^{2} + y^{2}}$
d)		$\frac{μ_{0}}{2 π} \frac{I (x \hat{i} - y \hat{i})}{x^{2} + y^{2}}$

14. A wire of length l is formed into a circular loop of one turn only is suspended in magnetic field B. When a current I is passed through the loop, the torque experienced by it is

a)		$\frac{1}{4 π} BIl$
b)		$\frac{1}{4 π} B^{2} Il$
c)		$\frac{1}{4 π} l^{2} IB$
d)		$\frac{1}{4 π} B I^{2} l$

15. Two insulated rings, one of slightly smaller diameter than the other are suspended along their common diameter as shown. Initially the planes of the rings are mutually perpendicular. When a steady current is set up in each of them
magnetiseffect-q12

a)		Two rings rotate into a common plane
b)		The inner ring oscillates about its initial position
c)		The outer ring stays stationary while the inner ring moves into the plane of the outer ring
d)		The inner ring stays stationary while the outer ring moves into the plane of the inner ring

16. An electron and a proton with equal momentum enter perpendicularly into a uniform magnetic field

a)		The path of proton shall be more curved than that of electron
b)		The path of proton shall be less curved than that of electron
c)		Both are equally curved
d)		Path of both particle will be straight line

17. An infinite straight conduction carrying current 2l is split into a loop of radius r as shown in the Figure. The magnetic field at the centre of the coil is
magnetiseffect-q10

a)		$\frac{μ_{0}}{4 π} \frac{2 (π + 1)}{r}$
b)		$\frac{μ_{0}}{4 π} \frac{2 (π - 1)}{r}$
c)		$\frac{μ_{0}}{4 π} \frac{(π + 1)}{r}$
d)		Zero

18. If the direction of the initial velocity of the charged particle is neither along nor perpendicular to that of the magnetic field, then the orbit will be

a)		A straight line
b)		An ellipse
c)		A circle
d)		A helix

19. Energy in a current carrying coil is stored in the form of

a)		Electric field
b)		Magnetic field
c)		Dielectric strength
d)		Heat

20. A current i ampere flows in a circular are of wire which subtends an angle ( $3 π / 2$ ) radians at its centre, whose radius is R. The magnetic induction B at the centre is

a)		$μ_{0} i / R$
b)		$μ_{0} i / 2 R$
c)		${2 μ}_{0} i / 4$
d)		${3 μ}_{0} i / 8 R$

21. The field normal to the plane of a wire of n turns and radius r which carries a current i is measured on the axis of the coil at a small distance x from the centre of the coil. This is smaller than the field at the centre by the fraction

a)		$\frac{3}{2} . \frac{x^{2}}{r^{2}}$
b)		$\frac{2}{3} . \frac{x^{2}}{r^{2}}$
c)		$\frac{3}{2} .$ $\frac{r^{2}}{x^{2}}$
d)		$\frac{2}{3} . \frac{r^{2}}{x^{2}}$

22. Electron and proton of equal momentum enter a uniform magnetic field normal to the lines of force. If the radii of curvature of circular paths be $r_{e}$ and $r_{p}$ respectively, then

a)		$r_{e} /$ $r_{p}$ = 1/1
b)		$r_{e} /$ $r_{p}$ = $m_{p} / m_{e}$
c)		$r_{e} /$ $r_{p}$ = $\sqrt{m_{p} / m_{e}}$
d)		$r_{e} /$ $r_{p}$ = $\sqrt{m_{e} / m_{p}}$

23. An infinitely long straight conductor is bent into the shape as shown in Figure. It carries a current of i ampere and the radius of the circular loop is r metre. Then the magnetic induction at the centre of the circular part is
magnetiseffect-q4

a)		Zero
b)		Infinite
c)		$\frac{μ_{0}}{4 π} .$ $\frac{2 i}{r} . (π + 1)$
d)		$\frac{μ_{0}}{4 π} .$ $\frac{2 i}{r} . (π - 1)$

24. Two straight long wires are set parallel to each other. Each carries a current i in the same direction and the seperation between them is 2r. The intensity of magnetic field at a distance r between the two wires is

a)		i/r
b)		2i/r
c)		4r/r
d)		Zero

25. Weber/ $m^{2}$ is equal to

a)		Henry
b)		Tesla
c)		Volt
d)		All of these

26. A wire of given length is first bent in one loop and the next time it is bent in three loops. If the same current is passed in both the cases the ratio of the magnetic field induction at the centres will be

a)		1 : 4
b)		1 : 9
c)		9 : 1
d)		1 : 3

27. A galvanometer of resistance 100 $Ω$ gives full scale deflection with 5mA current. In order to convert it into 5V range voltmeter the value of resistance connected in series will be

a)		1000 $Ω$
b)		900 $Ω$
c)		100 $Ω$
d)		10 $Ω$

28. To sent 10% of the main current through a moving coil galvanometer of resistance 99 $Ω$ the shunt required is

a)		100 $Ω$
b)		0.9 $Ω$
c)		9.9 $Ω$
d)		11 $Ω$

29. A circular coil carrying current has radius R. The distance from the centre to the coil on the axis where the magnetic induction will be 1/8 th to its value at the centre of the coil is

a)		$\frac{R}{\sqrt{3}}$
b)		$R \sqrt{3}$
c)		$2 R \sqrt{3}$
d)		$\frac{\sqrt{3}}{2 R}$

30. Two particle X and Y having equal charges after being accelerated through the same p.d enter a region of uniform magnetic field and describe circular paths of radi $R_{1}$ and $R_{2}$ . The ratio of the masses X and Y.

a)		${(\frac{R_{1}}{R_{2}})}^{Y_{2}}$
b)		$\frac{R_{1}}{R_{2}}$
c)		${(\frac{R_{1}}{R_{2}})}^{2}$
d)		$\frac{R_{2}}{R_{1}}$

31. A portion of a conducting wire is bent in the form of a semi-circle of radius r as shown. At the centre of the semicircle the magnetic induction will be
phmeec19

a)		zero
b)		infinite
c)		$\frac{μ_{0} i τ}{4 r}$
d)		$\frac{μ_{0} i τ}{2 r}$

32. An electron of mass m and charge e is moving in a circular orbit of radius r in a hydrogen atom. The angular momentum of the electron is L. The dipole moment associated with it is

a)		$\frac{e}{m e}$
b)		$\frac{L e}{2 m}$
c)		$\frac{2 m}{L e}$
d)		$\frac{m}{L e}$

33. A circular coil of radius 0.314 m carrying a current of 2A produces a magnetic field ${2 \times 10}^{- 4} T$ at its centre. The number of turns of the coil is

a)		25
b)		5
c)		50
d)		75

34. In a H- atom the electron is making ${6 \times 10}^{15}$ rps around the nucleus in an orbit of ${0.5 A}^{\circ}$ . The equivalent magnetic dipolemoment is

a)		${7.5 \times 10}^{- 23} {Am}^{2}$
b)		${7.5 \times 10}^{24} {Am}^{2}$
c)		${7.5 \times 10}^{- 24} {Am}^{2}$
d)		${7.5 \times 10}^{28} {Am}^{2}$

35. A $β$ -particle moving with a speed of $10^{6} m / s$ enters a region of uniform magnetic field of 0.2T as shown in the figure. The force experienced by $β$ - particle
phmeec15

a)		${1.6 \times 10}^{- 14} N$
b)		${2.77 \times 10}^{- 14} N$
c)		${3.2 \times 10}^{- 14} N$
d)		${1.6 \times 10}^{14} N$

36. A proton and an alpha particle enter in a uniform magnetic feld perpendicular with the same speed. If the periodic time of revolution of the proton in 5micro second, the periodic time of alpha particle is

a)		50 $μ s$
b)		2.5 $μ s$
c)		10 $μ s$
d)		5 $μ s$

37. Lorentz force on a charge q moving in a magnetic field B with velocity V is

a)		$\frac{Bq}{V}$
b)		$\frac{V \times B}{q}$
c)		$q (\vec{V} \times \vec{B})$
d)		$q (\vec{B}$ $\times \vec{V})$

38. A charged particle in a magnetic field experiences the maximum force when

a)		it is moving parallel to magnetic field
b)		it is at rest
c)		it is moving perpendicular to the magnetic field
d)		none of the above

39. Two parallel wires carrying current in opposite direction

a)		attract each other
b)		repel each other
c)		do not affect each other
d)		none of the above

40. The lines of magnetic induction around an infinite straight conductor carrying current are

a)		parallel to the conductor
b)		circular
c)		parabolie
d)		none of the above

41. A solenoid has n turns per metre length of the coil a current i ampere flows through it. The field at the centre is given by

a)		$\frac{μ_{0} n i}{2}$
b)		$\frac{μ_{0} n}{i}$
c)		$\frac{μ_{0} n i}{4 π}$
d)		$μ_{0} n i$

42. The vector form of Biot-Savart law is

a)		$\vec{dB} = \frac{μ_{0} i \vec{dl} \times \vec{r}}{4 π r^{2}}$
b)		$dB = \frac{μ_{0} i dl}{4 π r^{2}}$
c)		$\vec{dB} = \frac{μ_{0}}{4 π} \frac{\vec{dl} \times \vec{r}}{r^{3}}$
d)		$\vec{dB} = \frac{μ_{0 \vec{dl}}}{4 π r^{2}}$

43. A wire of length L metre carrying a current i ampere is bent in the form a circle. The magnitude of the magnetic moment is

a)		$\frac{iL}{4 π}$
b)		$\frac{i L^{2}}{4 π}$
c)		${4 π}^{2} L^{2} i$
d)		${π L}^{2} i$

44. Two infinitely long parallel wires carry equal current i flowing in opposite directions. The magnetic field exactly half way between the wires is

a)		zero
b)		$\frac{μ_{0}}{4 π}$ $\frac{2 i}{r}$
c)		$\frac{μ_{0}}{π} \frac{i^{2}}{r}$
d)		$\frac{μ_{0} i}{2 π r}$

45. Two long parallel wires are seperated by a distance r carry equal current i. The magnetic field of one exerts a force F on the other. The distance between them is related to r/2 and the current in each reduced to i/4. Now the force between them is

a)		$\frac{F}{8}$
b)		8F
c)		4F
d)		F

46. Pick out the one whose motion can not be deflected by a magnetic field

a)		proton
b)		electron
c)		neutron
d)		alpha rays

47. In a moving coil galvanometer the deflection of the coil is related to electric current as

a)		$i \infty \tan θ$
b)		$i \infty θ$
c)		$i$ $\infty \sqrt{θ}$
d)		$i \infty θ^{2}$

48. A current of 10A is flowing in a wire of length 1.5m. A force of 15N acts on it when it is placed in a uniform magnetic field of 2 Tesla. The angle between the direction of the magnetic field and the direction of current is

a)		$30^{\circ}$
b)		$45^{\circ}$
c)		$60^{\circ}$
d)		$75^{\circ}$

49. Two identical coils carrying equal currents have common centre but the planes of the coil are at right angles to each other. What is the magnitude of the resultant magnetic field at the centre, if the field due to one alone is B?

a)		zero
b)		B/2
c)		2B
d)		$\sqrt{2}$ B

50. A galvanometer has resistance of 40 $Ω$ and full scale deflection is obtained when a current of 10 mA passes through it. The value of the shunt which must be used with the meter so that full scale deflection is obtained for a current of 5A is passed through it.

a)		8 $Ω$
b)		0.8 $Ω$
c)		0.08 $Ω$
d)		80 $Ω$