Tag: electro-magnetism

Questions Related to electro-magnetism

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

Show answer
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

Show answer
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

Show answer
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

Show answer
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

Show answer
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.

Why are transformers used in the transmission of electric power?

physics electro-magnetism applications of electromagnets transformer transformers

  1. Because they can reduce transmission losses

  2. Because they can conserve electrical energy

  3. Because they speed up transmission

  4. Because they help to distribute electrical energy efficiently

Show answer
Correct Option: A,D
Explanation:

Transformer used in the transmission of electrical power because they help to distribute electrical energy efficiently and can reduce transmission loss.

Which of the following statement about the action of a transformer is correct?

physics electro-magnetism applications of electromagnets transformer transformers

  1. Alternating current always flows in the secondary coil when an alternating voltage is applied to the primary coil.

  2. The current in the secondary coil is always larger than the current in the primary coil.

  3. An e.m.f. is induced in the secondary coil when an alternating voltage is applied to the primary coil.

  4. An e.m.f. is induced in the secondary coil when a steady direct current flows in the primary coil.

Show answer
Correct Option: C
Explanation:

Alternating current does not flow in the secondary coil unless electrical load is connected to its terminals.
In step-up transformer current in secondary coil is less than the current in primary coil.
No e.m.f. is induced in the secondary coil if the primary coil is connected to a d.c. supply.

The current drawn by the primary of a transformer, which steps down 200 V to 20 V to operate a device of resistance 20 $\Omega$ is: (Assume the efficiency of the transformer to be 80 %)

physics electro-magnetism applications of electromagnets transformer transformers

  1. 0.125 A

  2. 0.225 A

  3. 0.325 A

  4. 0.425 A

Show answer
Correct Option: A
Explanation:
$V _{primary} =200\ V$
$V _{secondary}=20\ V$
$R=20\ \Omega$
Power secondary $=\dfrac {(V _{secondary}^2)}{R}$

                               $=20\ W$

Power primary $=\dfrac {20}{\dfrac {80}{100}}=25\ w\quad (80\%\ efficiency)$

Power primary $=(I _{primary}) (V _{primary})$
$25=I _P \times 200$
$I _P=0.125\ A$
Option $(A)$

In a step up transformer the turn ratio is 1:2. A Leclanche cell (emf = 1.5 V) is connected across the primary. The voltage across the secondary is

physics electro-magnetism applications of electromagnets transformer transformers

  1. 3.0 V

  2. 1.5 V

  3. 0.75 V

  4. 0

Show answer
Correct Option: A
Explanation:

For the step up transformer -

$\dfrac { { V } _{ 1 } }{ { V } _{ 2 } } =\dfrac { { n } _{ 1 } }{ { n } _{ 2 } } $

$\dfrac { 1.5 }{ { V } _{ 2 } } =\dfrac { 1 }{ 2 } $

$\Rightarrow { V } _{ 2 }=3V$.