Tag: magnetism and electromagnetism

Questions Related to magnetism and electromagnetism

Starter is used in

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. high power electric motors

  2. low power electric motors

  3. transformers

  4. galvanometer

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Correct Option: A
Explanation:

A starter (also self starter, self, or starter motor) is an electric motor, pneumatic motor, hydraulic motor, an internal-combustion engine in case of very large engines or other device used for rotating an internal-combustion engine so as to initiate the engine's operation under its own power.

To convert mechanical energy into electrical energy, one can use

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. $DC$ dynamo

  2. $AC$ dynomo

  3. motor

  4. transformer

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Correct Option: A,B
Explanation:

A dynamo converts mechanical energy to electrical energy, producing a DC current, using a commutator.
A motor converts various type of energy like fossil fuel, steam an electrical energy to mechanical energy.
A transformer magnetically couples different electrical circuits. 

A coil of inductance 0.1 H is connected to an alternating voltage generator of voltage E = 100 sin (100 t) volt. The current flowing through the coil will be 

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. $I = 10 \sqrt{2} sin (100t) A$

  2. $I = 10 \sqrt{2} cos (100t) A$

  3. $I = -10 sin (100 t)A$

  4. $I = -10 cos (100 t)A$

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Correct Option: D
Explanation:

L =$0.14$

E=$100sin(100t)$
$ \Rightarrow {X _L} = {w _L} = 100 \times 0.1$
$ = 10\Omega $
$\Rightarrow {i _ \circ } = \dfrac{{E \circ }}{{{X _L}}} = \dfrac{{100}}{{10}} = 10A$
$ \Rightarrow i = {i _ \circ }\sin \left( {100t - \dfrac{\pi }{2}} \right)$
$ \Rightarrow i =  - {i _ \circ }\sin \left( {\dfrac{\pi }{2} - 100} \right)$
So we get
$ \Rightarrow i =  - 10\cos \left( {100t} \right)A$
therefore, option $D$ is correct.

The essential difference between a d.c. dynamo and an a.c. dynamo is that

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. a.c. has an electromagnet but d.c. has a

    permanent magnet

  2. a.c. will generate a higher voltage

  3. a.c.has slip rings but the d.c. has a commutator

  4. a.c. dynamo hyas a coil wound on soft iron,

    but the d.c. dynamo has a coil wound on copper

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Correct Option: C
Explanation:

The a.c dynamo has step rings because it changes polarity in every half cycle.

A dynamo 

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. Creates mechanical energy

  2. Creates electrical energy

  3. Converts electrical energy into mechanical energy

  4. Converts mechanical energy into electrical energy

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Correct Option: D
Explanation:

Generally a small dynamo require a permanent magnet. Using the Faraday's law of induction, rotating a coil of wire and magnetic fields to convert mechanical rotation into a direct electric current. Thus, a dynamo converts mechanical energy to electrical energy.  

A dynamo is used to supply electric current to a small electric bulb, If the number of turns in the coil of this dynamo is doubled, then the voltage in the bulb.

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. Will decrease

  2. Remains unchanged

  3. Will be doubled

  4. Will increase by a factor between 1 and 2

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Correct Option: C
Explanation:

When the number of turns in the coil increases, the strength of the voltage induced in the coil will also increase as the number of turns and induced voltage are directly proportional to each other.
Therefore, if the number of turns in the coil of this dynamo is doubled, then the voltage in the bulb will also be doubled.

An electricity generating machine consists of a turbine and a______

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. Dynamo

  2. Core

  3. Heat

  4. Sun

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Correct Option: A
Explanation:
To generate electricity, we need a turbine & dynamo. Turbine rotates to give mechanical energy to dynamo & dynamo converts it to electrical energy.

A commutator changes the direction of current in the coil of

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. a DC motor

  2. a DC motor and an AC generator

  3. a DC motor and a DC generator

  4. an Ac generator

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Correct Option: C
Explanation:

The only difference between a DC generator and an AC generator is in the way the two ends of the generator coil are linked to the outer circuit.

What is a commutator?

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. A device that reverses the direction of flow of current through a circuit is called a commutator.

  2. A device that flows in the direction of flow of current through a circuit is called a commutator.

  3. A device that reverses the direction of flow of voltage through a circuit is called a commutator.

  4. All

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Correct Option: A
Explanation:

A device that reverses the direction of flow of current through a circuit is called a commutator. In electric motors, the split ring acts as a commutator.

Electric generator is classified on the bases of

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. peak of electric voltage produced.

  2. type of electric current produced.

  3. power produced.

  4. none

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Correct Option: B
Explanation:

An electric generator is classified on the basis of type of electric current it produces