JEE Physics Moving Charges and Magnetism MCQs Set B

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Question: A proton is accelerating in a cyclotron where the applied magnetic field is 2 T. If the potential gap is effectively 100 kV then how much revolutions the proton has to make between the “dees” to acquire a kinetic energy of 20 MeV?

• a) 100
• b) 100
• c) 200
• d) 300

Answer: 100

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• d)

  

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Question: At what distance on the axis, from the centre of a circular current carrying coil of radius r, the magnetic field becomes 1/8th of the magnetic field at centre?

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• d)

  

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• d)

  

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Question:

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• b)

  

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• d) Zero

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Question:

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• d) y = x

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Question:

• a) Opposite to OX
• b) Along OX
• c) Opposite to OY
• d) Along OY

Answer: Opposite to OX

Question:

• a) 12 ms^–2
• b) 1.2 × 10^–3 ms^–2
• c) 0.6 × 10^–3 ms^–2
• d) Zero

Answer: 12 ms^–2

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• a)

  

• b)

  

• c)

  

• d) Zero

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Question:

• a)

  

• b)

  

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• d) Zero

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• b)

  

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• d) Zero

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• c)

  

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Question: If the planes of two identical concentric coils are perpendicular and the magnetic moment of each coil is M, then the resultant magnetic moment of the two coils will be

• a)

  

• b) 3 M
• c) 2 M
• d) M

Answer:

Question: In a hydrogen atom, an electron of mass m and charge e revolves in an orbit of radius r making n revolutions per second. If the mass of hydrogen nucleus is M, the magnetic moment associated with the orbital motion of electron is

• a)

  

• b)

  

• c)

  

• d)

  

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Question: The phosphor bronze strip is used in a moving coil galvanometer because

• a) It is torsional constant is small
• b) It is easily available
• c) It is paramagnetic
• d) It is diamagnetic

Answer: It is torsional constant is small

Question:

• a)

  

• b)

  

• c)

  

• d) Zero

Answer:

Question:

• a) T
• b) 2T
• c) 3T
• d) 4T

Answer: T

Question: A beam of electrons is moving with constant velocity in a region having electric and magnetic fields of strength 20 Vm^–1 and 0.5 T at right angles to the direction of motion of the electrons. What is the velocity of the electrons? 

• a) 40 ms^–1
• b) 20 ms^–1
• c) 10 ms^–1
• d) 30 ms^–1

Answer: 40 ms^–1

Question:

• a) 11 cm
• b) 18 cm
• c) 12 cm
• d) 16 cm

Answer: 11 cm

Question: A positively charged particle moving due East enters a region of uniform magnetic field directed vertically upwards. This particle will

• a) Move in a circular path with a uniform speed
• b) Move in a circular path with a decreased speed
• c) Get deflected in vertically upward direction
• d) Move in circular path with an increased speed

Answer: Move in a circular path with a uniform speed

Question: An electron having mass m and kinetic energy E enters in uniform magnetic field B perpendicularly, then its frequency will be

• a)

  

• b)

  

• c)

  

• d)

  

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Question: An electron moves in a circular orbit with a uniform speed v. It produces a magnetic field B at the centre of the circle. The radius of the circle is proportional to

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• b)

  

• c)

  

• d)

  

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Question:

• a) Angle between can have any value other than zero and 180°
• b) Angle between can have any value other than 90°
• c) Angle between is necessarily 90°
• d) Angle between is either zero or 180°

Answer: Angle between can have any value other than zero and 180°

Question: Under the influence of a uniform magnetic field a charged particle is moving in a circle of radius R with constant speed v. The time period of the motion

• a) Is independent of both R and v
• b) Depends on v and not on R
• c) Depends on both R and v
• d) Depends on R and not on v

Answer: Is independent of both R and v

Question:

• a) 8 N in –z direction
• b) 8 N in z direction
• c) 4 N in z direction
• d) 8 N in y direction

Answer: 8 N in –z direction

Question:

• a) (b) & (c)
• b) (b) & (d)
• c) (c) & (d)
• d) (a) & (c)

Answer: (b) & (c)

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• b)

  

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• d)

  

Answer:

Question:

• a) vB, –y axis
• b) qvB, –y axis
• c) qvB, +y axis
• d)

  

Answer: vB, –y axis

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• b)

  

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Question:

• a) A net attractive force towards the conductor
• b) A net torque acting downward normal to the horizontal plane
• c) A net repulsive force away from the conductor
• d) A net torque acting upward perpendicular to the horizontal plane

Answer: A net attractive force towards the conductor

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• b)

  

• c)

  

• d)

  

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Question: Charge q is uniformly spread on a thin ring of radius R. The ring rotates about its axis with a uniform frequency f Hz. The magnitude of magnetic induction at the center of the ring is

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• b)

  

• c)

  

• d)

  

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Question: The magnetic field of given length of wire for single turn coil at its centre is B then its value for two turns coil for the same wire is

• a) 4B
• b)

  

• c) 2B
• d)

  

Answer: 4B

Question:

• a) Along Oy
• b) Opposite to Oy
• c) Along Ox
• d) Opposite to Ox

Answer: Along Oy

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• b)

  

• c)

  

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Answer:

Question:

• a) On AB
• b) On CD
• c) On both OD and BO
• d) On both AB and CD

Answer: On AB

Question: To convert a galvanometer into a voltmeter one should connect a

• a) High resistance in series with galvanometer
• b) High resistance in parallel with galvanometer
• c) Low resistance in series with galvanometer
• d) Low resistance in parallel with galvanometer

Answer: High resistance in series with galvanometer

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• b)

  

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• d)

  

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Question: A straight wire of a diameter 0.5 mm carrying a current of 1 A is replaced by another wire of 1 mm diameter carrying the same current. The strength of the magnetic field far away is

• a) No change  
• b) One-half of the earlier value
• c) One-quarter of the earlier value
• d) Twice the earlier value

Answer:  No change

Question:

• a) 1.5 × 10^–2 N.m
• b) 3 × 10^–2 N.m
• c) 1.5 × 10^–3 N.m
• d) 3 × 10^–3 N.m

Answer: 1.5 × 10^–2 N.m