Physics

Magnetism and Electromagnetism

1,019 Questions

This hub provides practice questions on magnetism and electromagnetism. It covers magnetic flux density, electromagnets, magnetic lines of force, and electromagnetic induction. These physics concepts frequently appear in technical and non-technical competitive exams.

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Magnetism and Electromagnetism Questions

Multiple choice thermodynamic principles of metallurgy general principles and processes of isolation of elements metallurgy chemistry

Permanent magnets can be made from :

  1. hard steel

  2. cobalt steel

  3. stainless steel

  4. wrought iron
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A permanent magnet is an object made from material that is magnetized and creates its own persistent magnetic field e.g. refrigerator magnet on its door. These are strongly attracted to magnets called as ferromagnetic and are made up of iron,nickel,cobalt and some alloys of rare earth metals.

Multiple choice thermodynamic principles of metallurgy general principles and processes of isolation of elements metallurgy chemistry

Magnetic ceramics or ferrites contain compounds of iron. These have been used:

  1. in panels for solar cells

  2. as memory elements in computers

  3. for building water-desalinators on ships

  4. for making transformers
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Magnetic ceramics or ferrites are used to store computer data in the residual magnetic fields of hard ferrite cores.

Multiple choice force and torque on a current carrying rectangular loop in a uniform magnetic field torque on current carrying loop force on current carrying conductor magnetic effects of current and magnetism physics

A bar magnet of moment $\overline{M}$ is in a magnetic field of induction $\overline{B}$. Then the couple is:

  1. $\overline{M}\times \overline{B}$
  2. $\overline{B}\times \overline{M}$
  3. $\overline{M} . \overline{B}$
  4. $\overline{B} . \overline{M}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$Torque = IAB \sin\theta$
$m = IA$
$T = mB \sin\theta$
$T = m \times B$

Multiple choice force and torque on a current carrying rectangular loop in a uniform magnetic field torque on current carrying loop force on current carrying conductor magnetic effects of current and magnetism physics

A magnetic field is produced and directed along y-axis. A magnet is placed along x-axis .The direction of the torque on the magnet is:

  1. in the x-y plane

  2. along z-axis

  3. along y-axis

  4. torque will be zero
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\tau =\vec{M}\times \vec{B}$
$\hat{i}\times \hat{j}=\hat{k}$
The direction of torque will be always $Z-axis (+ve)$

Multiple choice force and torque on a current carrying rectangular loop in a uniform magnetic field torque on current carrying loop force on current carrying conductor magnetic effects of current and magnetism physics

There is no couple acting when two bar magnets are placed co-axially separated by a distance because :

  1. there are no forces on the poles

  2. the forces are parallel and their lines of action do not cincide

  3. the forces are perpendicular to each other

  4. the forces act along the same line
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\vec{\tau} =\vec{M}\times \vec{B}=0$

$MB\sin \theta =0$
$\sin \theta =0$
$\Rightarrow \theta =0$
$\Rightarrow $ Magnetic field lines of both the magnets are in the same line which results in forces due to both magnets act along the same line

Multiple choice force and torque on a current carrying rectangular loop in a uniform magnetic field torque on current carrying loop force on current carrying conductor magnetic effects of current and magnetism physics

A current loop in a magnetic field

  1. can be in equilibrium in one orientation.

  2. can be in equilibrium in two orientations, both the equilibrium states are unstable.

  3. can be in equilibrium in two orientations, one stable while the other is unstable.

  4. experiences a torque where the field is uniform or non-uniform in all orientations.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A current loop is a magnetic field is in equilibrium in two orientations one is stable and another unstable.
$\because \vec{\tau} = \vec M \times \vec B = M  B  sin  \theta$
If $\theta = 0^o \Rightarrow \tau = 0$    (stable)
If $\theta = \pi \Rightarrow \tau = 0$     (unstable)
Do not experience a torque in some orientations
Hence option (c) is correct.

Multiple choice force and torque on a current carrying rectangular loop in a uniform magnetic field torque on current carrying loop force on current carrying conductor magnetic effects of current and magnetism physics

A current carrying coil tends to set itself____

  1. parallel to an external magnetic field.

  2. parallel to its own magnetic field

  3. perpendicular to the external magnetic field.

  4. perpendicular to the geographic meridian
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When current carrying coil is placed in the magnetic field torque acts on the coil. The torque acting on the coil will be zero if the coil and the magnetic field are perpendicular. Thus it orients such that the plane of coil is perpendicular to the field direction.

Multiple choice force and torque on a current carrying rectangular loop in a uniform magnetic field torque on current carrying loop force on current carrying conductor magnetic effects of current and magnetism physics

A magnetic needle kept non parallel to the magnetic field in a non uniform magnetic field experience.

  1. A force but not a torque

  2. A torque but not a force

  3. Both a force and a torque

  4. Neither a force nor a torque
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Magnetic needle can be considered as a magnetic dipole since it is placed in a non uniform magnetic field it will experience af force as magnetic force on both magnetic force will be different. Also, needle is placed non parallel to the field, so it will experience a torque also.

Therefore, C is correct option. 

Multiple choice physics electromagnetic waves properties and uses of different radiation electromagnetic spectrum spectrum

X - ray beam can be deflected by 

  1. Magnetic field

  2. Electric field

  3. Both (a) & (b)

  4. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$X-$rays aren't deflected by electrons and magnetic fields because $x-$rays do not carry and charge. They are electro-magnetic radiations and therefore cannot be deflected by electronic or any magnetic fields.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

Why is the iron core of a transformer  laminated (thin sheet) instead of being in one solid piece?

  1. To increase the energy losses due to eddy current

  2. To reduce the energy losses due to eddy current

  3. No reason

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The iron core of a transformer is made of Laminated silicon steel with special insulated coating to limit Eddy current loss. Electrical steel, also called lamination steel is specialty steel tailored to produce certain magnetic properties, such as a small hysteresis area (small energy dissipation per cycle, or low core loss) and high permeability.
An eddy current is a swirling current set up in a conductor in response to a changing magnetic field. By Lenz's law, the current swirls in such a way as to create a magnetic field opposing the change. To do this in a conductor, electrons swirl in a plane perpendicular to the magnetic field. Because of the tendency of eddy currents to oppose, eddy currents cause energy to be lost. More accurately, eddy currents transform more useful forms of energy, such as kinetic energy, into heat, which is generally much less useful. 

Multiple choice

Which of the following is an application of superconductors?

  1. Magnetic resonance imaging (MRI)

  2. Particle accelerators

  3. High-speed trains

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Superconductors are used in a variety of applications, including magnetic resonance imaging (MRI), particle accelerators, and high-speed trains.

Multiple choice

What is the name of the process by which Earth's magnetic field is generated?

  1. Dynamo Effect

  2. Convection Currents

  3. Coriolis Effect

  4. Precession
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The Dynamo Effect is the process by which Earth's magnetic field is generated due to the movement of molten iron in the Earth's outer core.

Multiple choice

What is the term used to describe the process by which a planet's magnetic field is generated?

  1. Dynamo Effect

  2. Convection Currents

  3. Coriolis Effect

  4. Solar Wind Interaction
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The Dynamo Effect is the process by which a planet's magnetic field is generated through the movement of electrically conducting fluids in its interior.

Multiple choice

What is the name of the phenomenon where magnetic activity modulates stellar pulsations?

  1. Magnetic Inhibition

  2. Magnetic Enhancement

  3. Magnetic Coupling

  4. Magnetic Damping
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Magnetic damping refers to the suppression of stellar pulsations by magnetic fields, which act as a brake on the pulsations.