Tag: applications of electromagnets

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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

In which of the following devices is an electromagnet used?
a. Electric tram
b. Loud speaker
c. Telegraph
d. Relay microphone

  1. a

  2. b, c and d

  3. a and b

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

An electromagnet is a temporary strong magnet made from a piece of soft iron when current flows in the coil wound around it. It is an artificial magnet and loses its magnetism when the current is removed. It is used in electric trams, loud speakers, telegraph, relay microphone etc to enhance the effect.

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.

Multiple choice physics applications of electromagnets

When the current through the electromagnet of a relay reaches a particular value.

  1. It breaks the circuit

  2. It opens the circuit by pulling in an iron contact

  3. It closes the circuit by pulling in an iron contact

  4. Both A or C
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A relay is an electromagnetic switch. Depending on the design, the movement of the iron contact can either open or close a secondary circuit when the electromagnet is energized.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

In the transformer phase difference between input and output is

  1. $0$

  2. $\dfrac {\pi}{2}$

  3. $\dfrac {\pi}{6}$

  4. $\pi$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In an ideal transformer, the primary and secondary voltages are in phase if the secondary is open-circuited, but they are in anti-phase (180 degrees or pi radians) due to Lenz's law when considering the induced EMF relative to the primary input.

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

Transformer are used

  1. in $DC$ circuits only

  2. in $AC$ circuits only

  3. in both $DC$ and $AC$ circuits

  4. neither in $DC$ nor in $AC$ circuits.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Transformer is an electrical device that requires time varying current to link two or more electrical coils through electromagnetic induction and thus transfer energy between the magnetically coupled circuits. Therefore transformer are used only in AC circuits

Multiple choice physics electro-magnetism applications of electromagnets transformer transformers

Why does the light of a car dim when the starter is operated?

  1. The starter motor draws a large current resulting in a large potential drop in the battery, which reduced the thermal voltage of the battery.

  2. When starter motor is switched on, it increases the resistance of the filament of the bulb in the car light.

  3. When the starter motor is switched on, it reduces the emf of the battery.

  4. The starter motor produces fumes, which absorb a part of the light of the car lamp.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since, the starter motor draws a large current resulting in a large potential drop in the battery, which reduced the thermal voltage of the battery hence, the light of a car are dim when the starter is operated.

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.