JEE Physics Moving Charges and Magnetism MCQs Set A

Question: Numerically 1 gauss = x tesla, then x is

• a) 10^–4
• b) 10⁴
• c) 10⁸
• d) 10^–8

Answer: 10^–4

Question: An electron having a charge e moves with a velocity v in positive x direction. A magnetic field acts on it in positive y direction. The force on the electron acts in (where outward direction is taken as positive z-axis).

• a) Negative direction of z-axis
• b) Positive direction of y-axis
• c) Negative direction of y-axis
• d) Positive direction of z-axis

Answer: Negative direction of z-axis

Question: If a proton enters perpendicularly a magnetic field with velocity v , then time period of revolution is T. If proton enters with velocity 2v, then time period will be

• a) T
• b) 2 T
• c) 3 T
• d) 4 T

Answer: T

Question:

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

Answer: 1 : 1 : 2

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: The net charge in a current carrying wire is zero still magnetic field exerts a force on it, because a magnetic field exerts force on

• a) Moving charge
• b) A negative charge only
• c) Stationary charge
• d) A positive charge only

Answer: Moving charge

Question: If a charged particle enters perpendicularly in the uniform magnetic field then

• a) Energy remains constant but momentum changes
• b) Energy and momentum both remains constant
• c) Momentum remains constant but energy changes
• d) Neither energy nor momentum remains constant

Answer: Energy remains constant but momentum changes

Question: The motion of a charged particle can be used to distinguish between a magnetic field and electric field in a certain region by firing the charge

• a) From opposite directions
• b) Perpendicular to the field
• c) Parallel to the field
• d) With different speeds

Answer: From opposite directions

Question: The correct expression for Lorentz force is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:  A charged particle moves in a gravity free space without change in velocity. Which of the following is not possible in that space?

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) 4 N, normal to the side towards centre of the triangle
• b) 4 N, normal to the side away from the centre of the triangle2 N, normal to the side away from the centre of the triangle
• c) 2 N, normal to the side away from the centre of the triangle
• d) 2 N, normal to the side towards centre of the triangle

Answer: 4 N, normal to the side towards centre of the triangle

Question: The oscillator frequency of a cyclotron is 10 MHz. What should be the operating magnetic field for accelerating proton?

• a) 0.656 T
• b) 0.356 T
• c) 0.256 T
• d) 0.156 T

Answer: 0.656 T

Question: A negative charge is coming towards the observer. The direction of the magnetic field produced by it will be (as seen by observer)

• a) Clockwise
• b) In the direction of motion of charge
• c) Anti-clockwise
• d) In the direction opposite to the motion of charge

Answer: Clockwise

Question: When equal current is passed through two coils, equal magnetic field is produced at their centres. If the ratio of number of turns in the coils is 8 : 15, then the ratio of their radii will be

• a) 8 : 15
• b) 1 : 2
• c) 15 : 8
• d) 1 : 1

Answer: 8 : 15

Question:

• a) R
• b) 2R
• c)

  

• d)

  

Answer: R

Question:

• a)

  

• b)

  

• c)

  

• d) Zero

Answer:

Question: Which one of the following graphs shows the variation of magnetic induction B with distance r from a long wire carrying a current?

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A current of i ampere is flowing in an equilateral triangle of side a. The magnetic induction at the centroid will be

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: If an electron revolves around a nucleus in a circular orbit of radius R with frequency n, then the magnetic field produced at the centre of the nucleus will be

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: The number of turns per unit length of a long solenoid is 10. If its average radius is 5 cm and it carries a current of 10 A, then the ratio of flux densities obtained at the centre and at the end on the axis will be

• a) 2 : 1
• b) 1 : 2
• c) 1 : 1
• d) 1 : 4

Answer:  2 : 1

Question:

• a) 10^–4
• b) 10^–7
• c) 10^–5
• d) 10^–6

Answer: 10^–4

Question: A conducting circular loop of radius r carries a constant current i. It is placed in uniform magnetic field B, such that B is perpendicular to the plane of the loop. The net magnetic force acting on the loop is

• a) Zero
• b)

  

• c)

  

• d)

  

Answer: Zero

Question:

• a) BIR
• b) 2BIR
• c) Zero
• d)

  

Answer: BIR

Question: If two straight current carrying wires are kept perpendicular to each other almost touching, then the wires

• a) Become parallel to each other
• b) Repel each other
• c) Attract each other
• d) Remain stationary

Answer: Become parallel to each other

Question: Connecting wires carrying currents in opposite directions are twisted together in using electrical appliances in order to reduce

• a) Magnetic effect
• b) Electrical effect
• c) Seebeck effect
• d) Peltier effect

Answer: Magnetic effect

Question:

• a) Move away from the wire
• b) Remain stationary
• c) Rotate about an axis parallel to the wire
• d) Move towards the wire

Answer: Move away from the wire

Question:

• a)

  

• b)

  

• c)

  

• d) Zero

Answer:

Question: Choose the correct statement

• a) All of these
• b) A moving charged particle can be accelerated by a magnetic field
• c) If a uniform magnetic field exists in a cubical region and zero outside then it is not possible to project a charged particle from outside into the field so that it describes a complete circle in the field
• d) It is possible for a current loop to stay without rotating in a uniform magnetic field

Answer: All of these

Question: The effective radius of a circular coil is R and number of turns is N. The current through it is i ampere. The work done in rotating the coil by angle of 180° in an external magnetic field B will be (initially plane of coil is perpendicular to magnetic field)

• a)

  

• b)

  

• c)

  

• d)

  Zero

Answer:

Question:  The current sensitivity of a moving coil galvanometer increases by 20% when its resistance is doubled. Calculate, by what factor does the voltage sensitivity change?

• a)

  

• b)

  

• c)

  

• d) No change

Answer:

Question: A charged particle enters a uniform magnetic field perpendicular to it. The magnetic field

• a) Changes the direction of motion of the particle
• b) Decreases the kinetic energy of the particle
• c) Increases the speed of the particle
• d) None of these

Answer:  Changes the direction of motion of the particle

Question:  A proton and an alpha particle enter the same magnetic field which is perpendicular to their velocity. If they have same kinetic energy then ratio of radii of their circular path is

• a) 1 : 1
• b) 1 : 2
• c) 2 : 1
• d) 1 : 4

Answer: 1 : 1

Question: In which of the following situations, the magnetic field can accelerate a charge particle at rest?

I. When the magnetic field is uniform with respect to time as well as position
II. When the magnetic field is time varying but uniform w.r.t. position
III. When the magnetic field is time independent but position dependent

• a) II only
• b) None of these
• c) III only
• d) I, II & III

Answer: II only

Question:

• a) All of these
• b)

  

• c)

  

• d)

  

Answer: All of these

Question: A proton moving with a constant velocity, passes through a region of space without change in its velocity. If E & B represent the electric and magnetic fields respectively, this region may have

• a)

  

• b)

  

• c) E & B both parallel
• d) E & B inclined at 45° angle

Answer: