Free Magnetic Flux Density MCQs with Answers

• A. weber
• B. tesla
• C. henry
• D. gauss

Explanation: One tesla is one weber per square metre, so the tesla measures flux density while the weber measures the total flux.

• A. F equals BIL sin theta
• B. F equals BIL cos theta
• C. F equals BI over L
• D. F equals B over IL

Explanation: The sine factor means the force is maximum when the conductor is perpendicular to the field and zero when it lies along the field, since a…

• A. the induced current in a generator
• B. the force on a current carrying conductor in a magnetic field
• C. the magnetic field around a wire
• D. the induced emf

Explanation: With the first finger along the field and the second along the current, the thumb gives the motion or force, which is the motor rule.

• A. straight lines parallel to the wire
• B. concentric circles centred on the wire
• C. lines radiating outwards from the wire
• D. no field at all

Explanation: The right hand grip rule gives the sense of the circles: point the thumb along the conventional current and the curled fingers show the…

• A. attract each other
• B. repel each other
• C. exert no force on each other
• D. twist about one another

Explanation: Each wire sits in the field of the other, and applying the left hand rule shows the forces to be inward when the currents are parallel…

• A. the coil experiences a constant torque whatever its angular position
• B. the coil turns faster
• C. the current is increased
• D. the coil never moves

Explanation: With curved pole pieces and a soft iron core the field is always parallel to the plane of the coil, so the torque stays proportional to…

• A. high resistance is connected in series
• B. low resistance called a shunt is connected in parallel
• C. high resistance is connected in parallel
• D. capacitor is connected in series

Explanation: The shunt carries most of the current so that only a small known fraction passes through the delicate coil, and it also keeps the overall…

• A. zero
• B. strongest at the ends
• C. nearly uniform and parallel to the axis
• D. circular around the axis

Explanation: The overlapping fields of the individual turns reinforce along the axis and largely cancel between adjacent turns, giving a field much…

• A. is cheaper
• B. loses its magnetism quickly when the current is switched off
• C. retains its magnetism permanently
• D. conducts electricity better

Explanation: An electromagnet must be able to be switched off, which requires a core of low retentivity, and soft iron is easily magnetised and just as…

• A. obey an inverse square law
• B. act only over a few millimetres
• C. are always attractive
• D. require a material medium

Explanation: Both fall off as one over the square of the separation and both can be attractive or repulsive depending on the sign or polarity involved.

• A. a net force that accelerates it across the field
• B. a torque that tends to align its plane perpendicular to the field
• C. neither force nor torque
• D. a force along the field lines

Explanation: The forces on opposite sides of the coil are equal and opposite, so they cancel and there is no net translational force, but because they…

• A. 5 tesla
• B. 50 microtesla
• C. 50 millitesla
• D. zero at the equator

Explanation: At around 50 microtesla the geomagnetic field is weak enough that a compass needle needs to be delicately mounted to respond to it, and…

• A. One gauss
• B. 3×10¹⁰ gauss
• C. 10⁴ gauss
• D. 1/3×10^-8 gauss

Explanation: Magnetic flux density is measured in tesla, and 1 tesla = 1 weber/m². Since 1 gauss = 10^-4 tesla, 1 weber/m² = 1 tesla = 10^4 gauss.

• A. Semiconductors
• B. Insulators
• C. Conductors
• D. None of these

Explanation: Ceramic magnets are made from ferrite materials, which have high electrical resistance and therefore behave as insulators.

• A. Magnetic intensity
• B. Magnetic moment
• C. Magnetic induction
• D. None of the above

Explanation: The tesla (T) is the SI unit of magnetic flux density, also called magnetic induction, B.

• A. repel each other
• B. not interact with each other
• C. attract each other
• D. be deflected normal to the plane containing the two beams.Educational Resources

Explanation: Two parallel beams of positrons produce electric repulsion because both beams carry positive charge.

• A. weaken it
• B. strengthen it
• C. reverse its polarity
• D. demagnetize it completely

Explanation: Heating disturbs the alignment of magnetic domains, so the magnet becomes weaker.

• A. 4πx10-9 WbA-1m-1
• B. 4πx10-7 WbA-1m-1
• C. 4πx10-10 WbA-1m-1
• D. 4πx10-8 WbA-1m-1

Explanation: The permeability of free space is μ0 = 4π x 10^-7 Wb A^-1 m^-1, equivalently N A^-2. The powers of ten in the other choices are incorrect.

• A. τ = NIAB cosφ
• B. τ = NIAB sinφ
• C. τ = NIAB tanφ
• D. τ = NIAB

Explanation: The torque on a current-carrying coil is τ = NIAB sinθ, where θ is the angle between the coil's normal and the magnetic field.

• A. charge in motion
• B. charge at rest
• C. both
• D. none

Explanation: A moving charge produces a magnetic field, and that field can exert torque on the magnetic needle of a compass.