Tag: physics

Questions Related to physics

The strength of an electromagnet can be increased by. 

physics electro-magnetism applications of electromagnets

  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

Show answer
Correct Option: A
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.

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

physics electro-magnetism applications of electromagnets

  1. soft iron

  2. steel

  3. brass

  4. copper

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Correct Option: A
Explanation:

Soft iron is used for making strong electromagnet.

Electromagnets are temporary magnets.

strength of electromagnet increases when

physics electro-magnetism applications of electromagnets

  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

Show answer
Correct Option: C
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) $

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   

physics electro-magnetism applications of electromagnets

  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

Show answer
Correct Option: A
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.

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:

physics electro-magnetism applications of electromagnets

  1. ${B _s} = - B$

  2. ${B _s} = 0$

  3. ${B _s} = B$

  4. ${B _s} < B but\,{B _s} \ne 0$

Show answer
Correct Option: B

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. 

physics electro-magnetism applications of electromagnets

  1. north pole

  2. south pole

  3. have no magnetic pole

  4. north and south pole any of that

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Correct Option: C

The phenomeno of paramagnetism is a consequnce of 

physics electro-magnetism applications of electromagnets

  1. Distortion effect.

  2. Orientation effect

  3. Both (A) and (B)

  4. Neither (A) nor (B)

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Correct Option: C

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

physics electro-magnetism applications of electromagnets

  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

Show answer
Correct Option: A
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.

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

physics applications of electromagnets

  1. South pole

  2. North pole

  3. Either $(1)$ or $(2)$

  4. Neither $(1)$ or $(2)$

Show answer
Correct Option: A
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

Electromagnets are used in

physics applications of electromagnets

  1. Electric bells

  2. Telephones

  3. Dynamos

  4. All of these

Show answer
Correct Option: D
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.