Untitled Document

Question Bank No: 1

1. Which of the following particle will have same frequency of revolution when projected with same velocity perpendicular to a magnetic field

a)		${Li}^{+ +}$
b)		${He}^{+ +}$
c)		proton
d)		electron

2. Four particles have same momentum which has maximum kinetic energy

a)		proton
b)		electron
c)		dentron
d)		$\propto$ - particle

3. If an ammeter is joined parallel through a circuit, it can be damaged due to excess

a)		resistance
b)		current
c)		voltage
d)		none of these

4. An arc of a circle of radius R subtends an angle $π / 2$ at the centre. It carries a current I. The magnetic field at the centre will be

a)		$\frac{μ_{0} I}{2 R}$
b)		$\frac{μ_{0} I}{4 R}$
c)		$\frac{μ_{0} I}{8 R}$
d)		$\frac{2 μ_{0} I}{5 R}$

5. The magnetic flux through a coreless solenoid carrying current I is 5 $\times 10^{- 6}$ cob. If the length of the solenoid is 25cm. Its magnetic moement is equal to

a)		1 A $m^{2}$
b)		10 A $m^{2}$
c)		12.5 A $m^{2}$
d)		125 A $m^{2}$

6. On connecting a battery to the two corners of a diagnonal of a square conductor frame of socle a, the magnitude of the magnetic field at the centre will be

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

7. An electron having mass and K.E E enter in a uniform magnetic field B perpendicularly, then its frequency will be

a)		$\frac{eE}{qmB}$
b)		$\frac{2 π m}{eB}$
c)		$\frac{eB}{2 π m}$
d)		$\frac{2 m}{eBE}$

8. The sensitivity of a moving coil galvanometer can be increased by

a)		increasing the number of turns in the coil
b)		decreasing the area of the coil
c)		increasing the current in the coil
d)		introducing a soft iron core inside the coil

9. Shunt required in an ammeter of resistance R to decrease its deflection from 30 ampere to 10 ampere is

a)		R/4
b)		R/3
c)		R/2
d)		R

10. If a long hollow copper pipe carries a current, the produced magnetic field will be

a)		inside the pipe only
b)		outside the pipe only
c)		both inside and outside the pipe
d)		neither inside nor outside the pipe

11. The expression for magnetic induction inside a solenoid of length L, carrying a current I and havinh N number of turns is

a)		$\frac{μ_{0} N}{4 π L} I$
b)		$μ_{0} NLI$
c)		$\frac{μ_{0}}{4 π} NLI$
d)		$μ_{0} \frac{N}{L} I$

12. An electron is accelerated by a potential of 500V. Its velocity is

a)		3/4 $\times 10^{7}$ m/s
b)		$10^{7}$ m/s
c)		$\frac{4}{3}$ $\times 10^{7}$ m/s
d)		0.25 $\times 10^{7}$ m/s

13. A charge of +q is moving upwards vertically. It enters a magnetic field directed to the north. The force on the charged will be towards

a)		north
b)		south
c)		west
d)		east

14. An electron of charge e moves with constant speed v along a circle of radius r. Its magnetic moment will be

a)		evr
b)		evr/2
c)		$π r^{2} ev$
d)		2 $π rev$

15. The resistance of ideal voltmeter is

a)		zero
b)		high
c)		infinite
d)		10 w

16. The deflection in moving coil galvanometer falls from 50 divisions to 10 divisions, when a short of 12 $Ω$ is applied, the resistance of the galvanometer coil is

a)		24 $Ω$
b)		12 $Ω$
c)		50 $Ω$
d)		48 $Ω$

17. The force between two parallel wires is 2 $\times 10^{- 7}$ N/m spaced 1m apart to each other in vacuum. The electric current flowing through the wire is

a)		unit ampere
b)		zero
c)		5 $\times 10^{6}$ ampere
d)		2 $\times 10^{- 7}$ ampere

18. Calculate force in a straight wire 11cm long carrying a current I = 12A when magnetic field around wire is 200 $μ T$ acting perpendicular to wire

a)		264 $μ$ N
b)		264 mN
c)		264 N
d)		264 kN

19. Two free parallel wires carrying currents in the opposite diections,

a)		attract each other
b)		repel each other
c)		neither b or c
d)		nothing can be said

20. A proton, a deutron and an $\propto$ - particle enter a magnetic field perpendicular to field with same velocity. What is the ratio of the radii of circular paths.

a)		1 : 2 : 2
b)		2 : 1 : 1
c)		1 : 1 : 2
d)		1: 2 : 1

21. The work done by a magnetic field on a moving charge is

a)		zero because $\vec{F}$ acts parallel to $\vec{V}$
b)		positive because $\vec{F}$ acts perpendiculat to $\vec{V}$
c)		zero because $\vec{F}$ acts perpendicular to $\vec{V}$
d)		negative because $\vec{F}$ acts paralle to $\vec{V}$

22. Ratio of magnetic field induction at the centre of a current carrying coil of radius r at a distance 3r on its axis is

a)		$\sqrt{10}$
b)		2 $\sqrt{10}$
c)		10 $\sqrt{10}$
d)		20 $\sqrt{10}$

23. A wire of length L meter carrying a current I ampere is bent in the form of a circle. Its magnitude of magnetic moment will be

a)		IL/ 4 $π$
b)		$I^{2} L^{2}$ / 4 $π^{2}$
c)		$I^{2}$ L/ 8 $π$
d)		I $L^{2}$ /8 $π$

24. The magnetic field at a distance r from a long wire carrying current i is 0.4 tesla. The magnetic field at a distance 2r is

a)		0.2 tesla
b)		0.8 tesla
c)		0.1 tesla
d)		1.6 tesla

25. A current of i ampere flows along an infinitely long straight thin walled tube, then the magnetic induction at any point inside the tube is

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

26. A current is passed through a straight wire. The magnetic field estalish around it has its lines of forces

a)		elliptical
b)		circular
c)		oval
d)		parabolic

27. The deflection in a moving coil galvanometers is reduced to half when shunted with 40 $Ω$ resistance. The resistance of the galvanomaters is

a)		80 $Ω$
b)		40 $Ω$
c)		15 $Ω$
d)		20 $Ω$

28. The orbital speed of electron orbiting around the nucleus in a circular orbit of radius 50pm is 2.2 $\times 10^{6}$ m $s^{- 1}$ . Then the magnetic dipole moment of an electron is

a)		1.6 $\times 10^{- 19}$ A $m^{2}$
b)		5.3 $\times 10^{- 21}$ A $m^{2}$
c)		8.8 $\times 10^{- 24}$ A $m^{2}$
d)		8.8 $\times 10^{- 26}$ A $m^{2}$

29. Two concentric circular current carrying loops is carrying current $l_{1}$ and $l_{2}$ have their radii in the ratio 1:2 and produce magnetic field at the common centre in the ratio 1:3 then value of ratio $\frac{l_{1}}{l_{2}}$ is

a)		1/4
b)		1/3
c)		1/6
d)		1/2

30. A particle of charge q coulomb moves in a circle of radius r metres, at n revolutions per second. The magnetic field intensity at the centre is

a)		$\frac{2 π q}{r}$ N $A^{- 1}$ $m^{- 1}$
b)		$\frac{2 π nq}{r} \times 10^{- 7} N$ $A^{- 1}$ $m^{- 1}$
c)		$\frac{2 π q}{nr} \times 10^{- 7}$ N $A^{- 1}$ $m^{- 1}$
d)		$\frac{2 π q}{r} \times 10^{- 7}$ N $A^{- 1}$ $m^{- 1}$

31. Helim nucleus travelling along a curved path in the magnetic field has velocity v. The velocity of proton moving in the same magnetic field along the same curved path will be

a)		v
b)		v/2
c)		2v
d)		4v

32. Two protons move parellel to each other with an equal velocity 300Km $s^{- 1}$ . If the two protons are moving at a perpendicular separation of $r_{m}$ then the force of electric interaction ${\vec{F}}_{e}$ is given by

a)		$\frac{e^{2}}{r^{3}}$ $\vec{r}$
b)		K $\frac{e^{2}}{r^{2}}$ $\vec{r}$
c)		$\frac{e^{2}}{r^{2}}$
d)		$\frac{1}{4 π \in_{0}}$ $\frac{e^{2}}{r^{3}}$ $\vec{r}$

33. Two protons move parellel to each other with an equal velocity 300Km $s^{- 1}$ . If the two protons are moving at a perpendicular separation of $r_{m}$ then magnetic induction due to one at the another proton will be

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

34. A cyclotron has frequency 10MHz and radius of its dees 60cm. The magnitude of operating magnetic field is

a)		0.96 T
b)		0.656 T
c)		0.56 T
d)		0.256 T

35. A current of 1A is flowing in an equilateral triangle of side 4.5 $\times 10^{- 2}$ m. The magnetic field at the centroid of the traingle is

a)		4 $\times 10^{- 5} T$
b)		3 $\times 10^{- 5}$ T
c)		$10^{- 5}$ T
d)		2 $\sqrt{3}$ $\times 10^{- 5}$ T

36. A rectangular loop of 2cm $\times 1.5$ cm is places in a magnetic field of 0.02T such that the face of the loop is parallel to the magnetic field. If number of turns in the coil is 1600 and carries a current of 50mA then torque on the coil is

a)		4.8 $\times 10^{- 3}$ Nm
b)		4.8Nm
c)		4.8 $\times 10^{- 2}$ Nm
d)		4.8 $\times 10^{- 4}$ NM

37. 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)		${2.2 \times 10}^{16} rad s^{- 1}$

38. A proton of mass 1.67 $\times 10^{- 27}$ kg is projected with a speed of 2 $\times 10^{6}$ m $s^{- 1}$ at an angle of $60^{o}$ to the x-axis. If a uniform magnetic field of 0.104 T is along y-axis, the path of proton is

a)		a circle of radius 0.2m and time period 2 $π \times 10^{- 7}$ s
b)		a helix of radius 0.2 m and time period 2 $π$ $\times 10^{- 7}$ s
c)		a circle of radius 0.1 m and time period 2 $π \times 10^{- 7}$ s
d)		a helix of radius 0.1m and time period 2 $π \times 10^{- 7}$ s

39. A square frame of side l carries a current I produces a field B at its centre. The same current is passed through a circular coil having the same perimeter as the square. The field at the centre of circular coil is $B^{'}$ . The ratio of $B^{'}$ /B is

a)		$\frac{π^{2}}{8 \sqrt{2}}$
b)		$\frac{8 π^{2}}{\sqrt{2}}$
c)		$\frac{3 π}{8 \sqrt{2}}$
d)		$\frac{π^{2}}{4 \sqrt{2}}$

40. The particle of mass m and charge 'q' is placed at rest in a uniform electric field E and then released. The KE attained by the particle after moving a distacne y is

a)		qE $y^{2}$
b)		qEy
c)		q $E^{2} y$
d)		$q^{2}$ Ey

41. In the figure, there are two semi circular rings of radius $r_{1}$ and $r_{2}$ in which a current I is flowing as shown. magneticeffectofcurrent-q12 The magnetic induction at centre O will be

a)		$\frac{μ_{0} I}{4} (r_{1} + r_{2})$
b)		$\frac{μ_{0} I}{4} (r_{1} - r_{2})$
c)		$\frac{μ_{0} I}{4} (\frac{r_{1} + r_{2}}{r_{1} r_{2}})$
d)		$\frac{μ_{0} I}{4} (\frac{r_{1} - r_{2}}{r_{1} r_{2}})$

42. In two parallel wires have current $I_{A}$ and $I_{B}$ in the same direction, the force between them is

a)		$\frac{μ_{0}}{2 π} \times \frac{I_{A} I_{B}}{r}$
b)		$\frac{I_{A} I_{B}}{r} μ_{0}$
c)		$\frac{{μ_{0} I}_{A}}{2 π (2 r)}$
d)		$\frac{{μ_{0} I}_{B}}{4 r}$

43. An electron is moving with a speed of $10^{8}$ m/s perpendicular to a uniform magnetic field of intensity B. Suddenly the intensity of magnetic field is reduced to B/2. The radius of the path becomes from the original value of r

a)		no change
b)		increases to r/2
c)		increases to 2r
d)		stops moving

44. A uniform electric field and a uniform magnetic field are produced, pointed in the same direction. An electron is projected with its velocity pointed in the same direction.

a)		the electron will turn to its right
b)		the electron will turn to its left
c)		the electron velocity will increase in magnitude
d)		the electron velocity will decrease in magnitude

45. The radius of curvature of the path of charged particle in a uniform magnetic field is directly proportional to

a)		the charge on the particle
b)		the momentum of the particle
c)		the energy of the particle
d)		the intensity of the field

46. A circular current carrying coil has a radius R. The distance from the centre of the coil, on the axis where the magnetic induction will be 1/ $8^{th}$ to its vale at the centre of the coil, is

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

47. Two particles X and Y having equal charges, after being accelerated through the same potential difference, enter a region of uniform magnetic field and describe circular paths if radii $R_{1}$ and $R_{2}$ respectively. The ratio of mass of X to that of Y

a)		${(R_{1} / R_{2})}^{1 / 2}$
b)		$R_{2} / R_{1}$
c)		${(R_{1} / R_{2})}^{2}$
d)		$R_{1} / R_{2}$

48. Two thin long parallel wires separated by a distance b are carrying a current i amp. each. The magnitude of the force per unit lenght exerted by one wire on the other is

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

49. The magnetic field dB due to a small current element dl at a distance r and element carrying current is

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

50. If a particle of charge $10^{- 1}$ C moving along the x-direction with a velocity of $10^{5}$ m/s experiences a force of $10^{- 10}$ N in y direction due to magnetic field, then the minimum value of magnetic field is

a)		6.25 $\times 10^{3}$ Tesla in z-direction
b)		6.25 $\times 10^{- 3}$ T in z-direction
c)		$10^{- 3}$ T in z-direction
d)		$10^{- 15}$ T in z-direction