Tag: applications of electromagnets

Questions Related to applications of electromagnets

State whether given statement is True or False
An autotransformer is one in which the primary and secondary are automatically coupled.

physics electro-magnetism applications of electromagnets transformer transformers

  1. True

  2. False

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Correct Option: B
Explanation:

An auto transformer is an electrical transformer with only one winding. The portion of the same winding acts both primary and secondary side of the transformer. 

In a transformer the number of turns in the primary coil is 200 and secondary coil is 600. The ratio between the electric current in the primary and secondary respectively is

physics electro-magnetism applications of electromagnets transformer transformers

  1. 1 : 4

  2. 4 : 1

  3. 1 : 3

  4. 3 : 1

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Correct Option: D
Explanation:

In a transformer, we know that 
$\frac{V _2}{V _1}=\frac{N _2}{N _1}$
where $V _1$ and $V _2$ are voltage across primary and secondary coils respectively and $N _1$ and $N _2$ are respective number of turns. 

Also, the transformer doesn't add or take away energy, so the power in
the primary and secondary is equal:
$V _1I _1=V _2I _2$
Therefore, $\frac{I _1}{I _2}=\frac{N _2}{N _1}$ 
$\frac{I _1}{I _2}=\frac{600}{200}=\frac{3}{1}$ 
Hence, desired ratio is 3:1. (D)

In transformer, core is made of soft iron to reduce

physics electro-magnetism applications of electromagnets transformer transformers

  1. Hysteresis losses

  2. Eddy current losses

  3. Force opposing electric current

  4. None of the above

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Correct Option: A
Explanation:

Transformer cores are made up of soft iron because soft iron has less losses due to hysteresis.

The quantity that remains unchanged in the output with respect to the input in an ideal transformer is

physics electro-magnetism applications of electromagnets transformer transformers

  1. Voltage

  2. Current

  3. Frequency

  4. None of these

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Correct Option: C
Explanation:

Transformer does not change the frequency of input AC.

Transformer works on.

physics electro-magnetism applications of electromagnets transformer transformers

  1. AC only

  2. DC only

  3. Both AC and DC

  4. AC more effectively than DC

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Correct Option: A
Explanation:

Transformer works on the principle of Electromagnetic induction i.e an emf is induced in the coil if the magnetic flux linked with the coil changes. Magnetic flux in the coil can change only in case of AC voltage supply. In case of DC voltage supply, magnetic flux in the secondary coil remains constant and thus no emf is induced in the secondary coil and so transformer cannot work in case of DC supply.
That's why, transformer can work on AC only.

A transformer is employed to

physics electro-magnetism applications of electromagnets transformer transformers

  1. convert A.C. into D.C.

  2. covert D.C into A.C

  3. obtain a suitable A.C voltage

  4. obtain a suitable D.C voltage

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Correct Option: C
Explanation:

C

A transformer is a device that is used to either raise or lower voltage, and currents in an electric circuit. Thereby, we can suitably obtain the voltage and current.

To increase the voltage of alternative current, we can use.

physics electro-magnetism applications of electromagnets transformer transformers

  1. Inverter

  2. Transformer

  3. Capacitor

  4. Rectifier

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Correct Option: B
Explanation:

Transformer is an apparatus for reducing or increasing the voltage of an alternating current.

Which of  the following has its working based on electromagnetic induction -

physics electro-magnetism applications of electromagnets transformer transformers

  1. Ammeter

  2. Voltmeter

  3. Transformer

  4. Galvanometer

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Correct Option: C
Explanation:

C

Electromagnetic Induction is the production of an emf across an electrical conductor in aa changing magnetic field in a transformer the alternating current through the primary winding produces a continually changing flux and die to this alternating flux on emf is induced in the secondary winding.

Read the following statements and answer whether the given statement is true or false.


A transformer is an electrical device that works on the principle of self-induction

physics electro-magnetism applications of electromagnets transformer transformers

  1. True

  2. False

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Correct Option: B
Explanation:

False

A transformer consists of two electrically isolated coils and operates on Faraday’s principle of mutual induction, in which an EMF is induced in the transformer secondary coil due to the magnetic flux generated by the voltages and currents flowing in the primary coil working. In self induction there is only one coil and emf is induced in that coil due to the change in flux linked with that coil. 

A transformer works on both A.C. and D.C.

physics electro-magnetism applications of electromagnets transformer transformers

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

False

Transformer does not work on DC. Direct current doesn’t have a variable magnetic field induced if fed through the primary winding of a transformer. Thus, only a constant magnetic field will act on secondary and shall not induce any voltage across the terminals of the same.