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

which part of a magnet attracts more iron fillings

  1. both the poles

  2. north pole

  3. south pole

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Magnetic field lines are most concentrated at the poles of a magnet, resulting in the strongest magnetic force being exerted at these locations.

Multiple choice

which part of a magnet attracts more iron fillings

  1. both the poles

  2. north pole

  3. south pole

  4. none of these

  5. can't say
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Magnetic field lines are most concentrated at the poles of a magnet, resulting in the strongest magnetic force being exerted at these locations.

Multiple choice physics electro-magnetism applications of electromagnets

The strength of an electromagnet can be increased by. 

  1. increasing the current in the coil

  2. decreasing the current in the coil

  3. decreasing the number of turns in the coil

  4. increasing the length of air gap between its poles
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer is A.

The strength of an electromagnet can be increased by increasing the number of loops of wire around the iron core and by increasing the current or voltage.

Multiple choice physics electro-magnetism applications of electromagnets

For making a strong electromagnet, the material of the core should be

  1. soft iron

  2. steel

  3. brass

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

Soft iron is used for making strong electromagnet.

Electromagnets are temporary magnets.

Multiple choice physics electro-magnetism applications of electromagnets

strength of electromagnet increases when

  1. the number of turns in the coil increases

  2. the current flowing in the coil increases

  3. both a and b

  4. the number of turns in the coil decreases
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
we know that
$\vec B=\dfrac{\mu NI}{L}$ where,
$\vec B$= Magnetic strength
N= number of turns
I= Current
L= Length of coil gap, and
$\vec B=\text{ magnetic field }\propto N$
$\vec B \propto I$
$\vec B\propto 1/2$
Thus
$B\left( \uparrow  \right) \text{ with } N\left( \uparrow  \right) \text{ and }I\left( \uparrow  \right) $

Multiple choice physics electro-magnetism applications of electromagnets

Two electromagnets are made by wrapping a few turns of wire on similar nails and passing the same amount of electric current through them.The number of turn of the wire wrapped over the two iron nails are in the ratio 2:1.The strength of   

  1. The first electromagnet will be greater

  2. The second electromagnet will be greater

  3. Both the electromagnets will be equal

  4. Electromagnets has no relation with the number of turns
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

More the number of coils, more will be the magnetic field produced in the electromagnets and hence made the electromagnet stronger. As number of turns wrapped on the first iron nail is more, thus the first electromagnet has more strength.

Multiple choice physics electro-magnetism applications of electromagnets

An example of a perfect diamagnet is a superconductor . This implies that when a superconductor is put in a magnetic field of intensity $B$, the magnetic field ${B _s}$ inside the superconductor will be such that:

  1. ${B _s} = - B$
  2. ${B _s} = 0$
  3. ${B _s} = B$
  4. ${B _s} < B but\,{B _s} \ne 0$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A perfect diamagnet (superconductor) exhibits the Meissner effect, where it expels all magnetic flux from its interior, resulting in a magnetic field of zero inside.

Multiple choice physics electro-magnetism applications of electromagnets

One bar magnet and one coil both are in a steady state. North pole of the magnet is towards the coil, then this end of the coil becomes. 

  1. north pole

  2. south pole

  3. have no magnetic pole

  4. north and south pole any of that
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

If the magnet and coil are in a steady state (no relative motion), there is no change in magnetic flux through the coil. Therefore, no induced current is produced, and the coil does not act as a magnet.

Multiple choice physics electro-magnetism applications of electromagnets

The phenomeno of paramagnetism is a consequnce of 

  1. Distortion effect.

  2. Orientation effect

  3. Both (A) and (B)

  4. Neither (A) nor (B)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Paramagnetism arises from the tendency of atomic magnetic moments to align with an external field (orientation effect) and the competition against thermal agitation (distortion effect).

Multiple choice physics electro-magnetism applications of electromagnets

Complete the given statement, the strength of an electromagnet can be:

  1. increased by adding a ferromagnetic core

  2. decreased by adding turns of wire to the coil

  3. increased by reducing the current through the wire

  4. increased by adding an aluminum core

  5. decreased by adding more layers of wire to the coil
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A ferromagnetic substance get highly magnetized when put in a magnetic field. When the ferromagnetic core is added to the electromagnet then the total field is the sum of the field because of electromagnet and because of the highly magnetized core.

Multiple choice physics applications of electromagnets

When a magnet is moved with its south pole towards a closed coil, the nearer end of the coil acts like a

  1. South pole

  2. North pole
  3. Either $(1)$ or $(2)$
  4. Neither $(1)$ or $(2)$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Lenz's law a law stating that the direction of an induced current is always such as to oppose the change in the circuit or the magnetic field that produces it.
When a magnet is moved with its south pole towards a closed coil, the nearer end of the coil acts according the lenz law The EMF induced is opposite direction.

When a magnet is moved with its south pole towards a closed coil, the nearer end of the coil acts like a south pole

Multiple choice physics applications of electromagnets

Electromagnets are used in

  1. Electric bells

  2. Telephones

  3. Dynamos

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

An electric bell is a mechanical bell that functions by means of an electromagnet. When an electric current is applied, it produces a repetitive buzzing or clanging.

When you speak to a friend through the telephone, your sound will be converted into electric current by the mouthpiece of the telephone. The current produced is a varying current and the frequency of the current will be the same as the frequency of your sound. The current will be sent to the earpiece of the telephone of your friend.

When the current passes through the solenoid, the iron core is magnetised. The strength of the magnetic field changes according to the varying current. When the current is high, the magnetic field will become stronger and when the current is low, the magnetic field become weaker.
The soft-iron diaphragm is pulled by the electromagnet and vibrates at the frequency of the varying current. The air around the diaphragm is stretched and compressed and produces sound wave. The frequency of the sound produced in the telephone earpiece will be the same as your sound.

Dynamos and Generators convert mechanical rotation into electric power. Dynamo is a device that makes direct current electric power using electromagnetism.

Multiple choice physics applications of electromagnets

Electromagnets are used in

  1. electric bells only

  2. telephones only

  3. dynamos only

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

An electromagnet is a soft metal core made into a magnet by the passage of electric current through a coil surrounding it. It has a number of applications including electric bells, in telephones and in dynamos.

Multiple choice physics applications of electromagnets

Electromagnets are used in

  1. electric bells only.

  2. telephones only.

  3. dynamos only.

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

Electromagnets are fundamental components in electric bells, telephones, and dynamos, as they allow for the conversion of electrical energy into mechanical motion or magnetic fields.

Multiple choice physics applications of electromagnets

Match the following

1. Industrial use a. Study of magnetic properties under magnetic field
2. Scientific use b. Removing pieces of iron from wounds
3. Medical use c. To separate iron filaments from other waster
4. Easiest method d. Lifting and transporting heavy loads of iron mass
  1. $1-d, 2-a, 3-b, 4-c$
  2. $1-b, 2-d, 3-c, 4-a$
  3. $1-c, 2-b, 3-a, 4-d$
  4. $1-a, 2-c, 3-d, 4-b$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electromagnets are used for various industrial, scientific, medical purposes mentioned above.