BITSAT Physics Moving Charges and Magnetism MCQs

Question: Two very long, straight, parallel wires carry steady currents I and -I respectively. The distance between the wires is d. At a certain instant of time, a point charge q is at a point equidistant from the two wires, in the plane of the wires. Its instantaneous velocity v is perpendicular to this plane. The magnitude of the force due to the magnetic field acting on the charge at this instant is

• a)

  

• b)

  

• c)

  

• d) 0

Answer: 0

Question: A charged particle moves through a magnetic field perpendicular to its direction. Then

• a) Kinetic energy changes but the momentum is constant
• b) The momentum changes but the kinetic energy is constant
• c) Both momentum and kinetic energy of the particle are not constant
• d) Both momentum and kinetic energy of the particle are constant

Answer: The momentum changes but the kinetic energy is constant

Question: A wire carrying current I has the shape as shown in adjoining figure. Linear parts of the wire are very long and parallel to X-axis while semicircular portion of radius R is lying in Y-Z plane. Magnetic field at point O is :

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A deuteron of kinetic energy 50 keV is describing a circular orbit of radius 0.5 metre in a plane perpendicular to the magnetic field B. The kinetic energy of the proton that describes a circular orbit of radius 0.5 metre in the same plane with the same B is

• a) 25 keV
• b) 50 keV
• c) 200 keV
• d) 100 keV

Answer: 100 keV

Question: A long straight wire along the Z-axis carries a current I in the negative Z-direction. The magnetic vector field B r at a point having coordinates (x, y) in the Z = 0 plane is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A charged particle with velocity 2 × 10³ m/s passes undeflected through electric and magnetic field. Magnetic field is 1.5 tesla. The electric field intensity would be

• a) 2 × 10³ N/C
• b) 1.5 × 10³ N/C
• c) 3 × 10³ N/C
• d) 4/3 × 10^–3 N/C

Answer: 3 × 10³ N/C

Question: A small current element of length dl and carryingcurrent is placed at (1, 1, 0) and is carrying current in ‘+z’ direction. If magnetic field at origin be  and at point (2, 2, 0) be  then

• a)

    =

• b)

  || = |2|

• c)

   =  -

• d)

  = -2

Answer:

 =  -

Question: Field inside a solenoid is

• a) Directly proportional to its length
• b) Directly proportional to current
• c) Inversely proportional to number of turns
• d) Inversely proportional to current

Answer: Directly proportional to current

Question: A uniform electric field and uniform magnetic field are acting along the same direction in a certain region. If an electron is projected in the region such that its velocity is pointed along the direction of fields, then the electron

• a) Will turn towards right of direction of motion
• b) Speed will decrease
• c) Speed will increase
• d) Will turn towards left direction of motion

Answer: Speed will decrease

Question: A horizontal overhead powerline is at height of 4m from the ground and carries a current of 100A from east to west. The magnetic field directly below it on the ground is (μ0 = 4π × 10^–7 Tm A^–1)

• a) 2.5×10^–7 T southward
• b) 5 × 10^–6 T northward
• c) 5 × 10^–6 T southward
• d) 2.5 × 10^–7 T northward

Answer: 5 × 10^–6 T southward

Question: If m is magnetic moment and B is the magnetic field, then the torque is given by

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A steady current is set up in a cubic network composed of wires of equal resistance and length d as shown in figure. What is the magnetic field at the centre P due to the cubic network

• a)

  

• b)

  

• c) 0
• d)

  

Answer: 0

Question: The magnetic field at the origin due to the current flowing in the wire is –

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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

• a)

  

• b)

  

• c) zero
• d)

  

Answer: zero

Question: An ammeter reads upto 1 ampere. Its internal resistance is 0.81ohm. To increase the range to 10 A the value of the required shunt is

• a) 0.03Ω
• b) 0.3Ω
• c) 0.9Ω
• d) 0.09Ω

Answer: 0.09Ω

Question: Two parallel wires carrying currents in the same direction attract each other because of

• a) Mutual inductance between them
• b) Potential difference between them
• c) Electric forces between them
• d) Magnetic forces between them

Answer: Magnetic forces between them

Question: Calculate the magnetic field at the centre of a coil in the form of a square of side 2a carrying a current I.

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: The work done by a magnetic field, on a moving charge is

• a) zero because acts parallel to
• b) Positive because acts perpendicular to
• c) Zero because acts perpendicular to
• d) Negative because acts parallel to

Answer: Zero because acts perpendicular to

Question: A circular loop of radius 0.3 cm lies parallel to a much bigger circular loop of radius 20 cm. The centre of the smaller loop is on the axis of the bigger loop. The distance between their centres is 15 cm. If a current of 2.0 A flows through the smaller loop, then the flux linked with bigger loop

• a) 9.1 × 10^–11 weber
• b) 6 × 10^–11 weber
• c) 3.3 × 10^–11 weber
• d) 6.6 × 10^–9 weber

Answer: 9.1 × 10^–11 weber

Question: A particle is moving with velocity and it produces an electric field at a point given by . It will produce magnetic field at that point equal to (all quantities are in SI units) [

• a)

  

• b)

  

• c) zero
• d) cannot be determined from the given data

Answer: