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Question Bank No: 3

1. A current carrying loop is free to turn in a uniform magnetic field. The loop will then come into equilibrium when its plane is inclined at (w.r to direction of field)

a)		$0^{0}$
b)		$45^{0}$
c)		$135^{0}$
d)		$90^{0}$

2. Which of the following represent 'tesla'?

a)		${NsC}^{- 1}$
b)		${Ns}^{- 1} C^{- 1} m^{- 1}$
c)		${Ns}^{- 2} C^{- 1} m$
d)		${NsC}^{- 1} m^{- 1}$

3. The dimensions of magnetic field intensity 'B' is

a)		${MLT}^{- 2} I^{- 1}$
b)		${MLT}^{- 1} I^{- 1}$
c)		${MT}^{- 1} I^{- 1}$
d)		${ML}^{2} T^{2}$

4. The frequency of an electron circulating at right angles to a uniform magnetic field does not depend upon

a)		speed of the charge
b)		mass of the charge
c)		charge of the particle
d)		magnetic field 'B'

5. Two identical coins carry equal currents and have common centre but the planes of the coils 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 coil alone is 'B'?

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

6. The magnetic field at a point P which is at a distance of 4cm from a long current carrying conductor is $10^{- 3} T$ . The magnetic field at a distance of 12cm from the conductor is

a)		$3.33 \times 10^{- 4} T$
b)		$3.33 \times 10^{- 3} T$
c)		$6.5 \times 10^{- 3} T$
d)		$2.5 \times 10^{- 8} T$

7. A stright conductor carries a current of 5A. An electron travelling with a speed of $5 \times 10^{6}$ m/s parallel to the wire at a distance of 0.1m from the conductor , experiences a force of

a)		$8 \times 10^{- 20} N$
b)		$3.2 \times 10^{- 19} N$
c)		$8 \times 10^{- 18} N$
d)		$1.6 \times 10^{- 19} N$

8. Two galvanometers A and B require 3 mA and 5 mA respectively to produce the same deflection of 10 divisions. Then

a)		A is more sensitive than B
b)		B is more sensitive than A
c)		A and B are equally sensitive
d)		sensitiveness of B is twice that of A

9. A charged particle travels along a straight line with a speed v in a region where both electric field E and magnetic fields B are present. It follows that

a)		E = vB and the two fields are parallel
b)		E = vB and the two fields are perpendicular
c)		B = vE and the two fields are parallel
d)		B = vE and the two fields are perpendicular

10. A solenoid of length 50 cm and a radius of cross section 1cm has 1000 turns of wire wound over it. If the current carried is 5A, the magnetic field on its axis, near the centre of the solenoid is approximately (permeability of free space, $μ_{0} = 4 π \times 10^{- 7} Tm / A$ )

a)		$0.6 \times 10^{- 2} T$
b)		$1.26 \times 10^{- 2} T$
c)		$2.51 \times 10^{- 2} T$
d)		$6.3 \times 10^{- 2} T$

11. The force on a conductor of length l placed in a magnetic field of magnitude B and carrying a current I is given by ( $θ$ is the angle the conductor makes with the direction of B)

a)		F = IlB sin $θ$
b)		$F = I^{2} {l B}^{2} \sin θ$
c)		$F = I l B \cos θ$
d)		$F = I^{2} l \sin θ / B$

12. A current carrying loop is placed in a uniform magnetic field. The torque acting on it does not depend on

a)		shape of the loop
b)		area of the loop
c)		number of turns in the loop
d)		strength of the current

13. Two long stright parallel conductors seperated by a distance of 0.5m carry currents of 5A and 8A in the same direction. The force per unit length experienced by each other is

a)		$1.6 \times 10^{- 5} N$ (attractive)
b)		$1.6 \times 10^{- 5} N$ (repulsive)
c)		$16 \times 10^{- 5} N$ (attractive)
d)		$16 \times 10^{- 5} N$ (repulsive)

14. A wire of certain length carries a steady current. It is first bent to form a circular coil of 1 turn. The same wire is next bent to form a circular coil of 3 turns. The ratio of magnetic induction at the centre of the coil in the two cases is

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

15. A circular coil of 20 turns and radius 10 cm is placed in a uniform magnetic field of 0.01T normal to the plane of the coil. If the current in the coil is 5A, the force and torque acting on it are respectively

a)		$F = 0, τ = 7.85 \times 10^{- 3} Nm$
b)		$F = 0, τ = 0.0157 Nm$
c)		$τ = 0, F = 0.0157 N$
d)		$F = 0, τ = 0$

16. A horizontal overhead power line carries a current of 100A from east to west. The magnetic field at point 5m below the line is

a)		$4 \times 10^{- 6} T,$ towards north
b)		$4 \times 10^{6} T,$ towards south
c)		$40 \times 10^{6} T,$ towards north
d)		$4 \times 10^{- 6} T,$ towards south

17. The force acting on a wire of length 0.05m placed inside a long solenoid near its centre making an angle of $30^{0}$ with the axis of the solenoid, if the wire carries a current of 10A and magnetic field due to the solenoid is 0.2T is

a)		0.5N
b)		0.05 N
c)		0.005 N
d)		5N

18. Two straight wires each one meter long are parallel to one another and are each carrying a current of 40A in the same direction. The force between the wires if the distance between the wires is 0.02m is

a)		$8 \times 10^{- 3} N$ , attractive
b)		$8 \times 10^{- 3} N$ , repulsive
c)		$16 \times 10^{- 3} N$ , repulsive
d)		$16 \times 10^{- 3} N$ , attractive

19. A solenoid has mean diameter of 0.05m and length 2m. It has 4 layers of 1000 turns each and a current of 2.5A flows through it. The magnetic field at a point on the axis neat its one end is

a)		$3.14 \times 1 0^{3} T$
b)		$3.14 \times 1 0^{3} T$
c)		$3.14 \times 1 0^{- 4} T$
d)		$3.14 \times 1 0^{- 3} T$

20. A circular coil of wire of 50 turns and radius 0.05m carries a current of 1A. The wire is suspended vertically in a uniform magnetic field of strngth 1.5 T. Direction of magnetric field is parallel to the plane of the coil. The torque on the coil is

a)		0.589 J
b)		0.859 J
c)		0.958 J
d)		5.89 J

21. A moving coil galvanometer of resistance 10 $Ω$ gives a full scale deflection for a current of 15mA, the shunt required to obtain an ammeter to measure 3A current

a)		5 ohm
b)		0.5 ohm
c)		2.5 ohm
d)		0.05 ohm

22. Chose the wrong statement. Sensitivity of a galvanometer is increased by

a)		increasing number of turns
b)		increasing the strength of field
c)		inserting soft iron cylinder inside the coil
d)		using suspension fibre of high restoring couple

23. The specific resistance of a wire 1.1m long 0.4mm in diameter and having a total resistance of 4.2 ohm will be

a)		$4.97 \times 10^{5} Ω m$
b)		$48 \times 10^{- 8} Ω m$
c)		$48 \times 10^{4} Ω m$
d)		$48 \times 10^{3} Ω m$

24. The capacity of storage cell is 2.5Ah. What is the maximum current that it can supply for half an hour?

a)		0.5A
b)		1A
c)		2.5 A
d)		5 A

25. A certain piece of copper is to be shaped into a wire of minimum resistance. Its length and diameter should be

a)		L, D
b)		2L,D
c)		L/2, 2D
d)		2L, D/2

26. The smallest resistance that can be obtained by the combination of 'n' resistors each of resistance R is

a)		$R / n^{2}$
b)		R/n
c)		nR
d)		$n^{2} R$

27. Wheatstone Bridge is used to measure

a)		emf
b)		potential
c)		resistance
d)		current

28. Pick out the odd one out of the following

a)		point charge
b)		uniformly charged sphere
c)		uniformly charged cube
d)		uniformly charged sheet

29. Ten identical resistors each 1 $Ω$ are joined in parallel. The combination has resistance

a)		10 $Ω$
b)		1 $Ω$
c)		0.1 $Ω$
d)		0.01 $Ω$