Tag: magnetism and electromagnetism

Quizzes (6) Questions (43)

Questions Related to magnetism and electromagnetism

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

Starter is used in

  1. high power electric motors

  2. low power electric motors

  3. transformers

  4. galvanometer
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

To convert mechanical energy into electrical energy, one can use

  1. $DC$ dynamo

  2. $AC$ dynomo

  3. motor

  4. transformer
Reveal answer Fill a bubble to check yourself
A,B Correct answer
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. 

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

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 

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

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

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

  4. $I = -10 cos (100 t)A$
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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

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

A dynamo 

  1. Creates mechanical energy

  2. Creates electrical energy

  3. Converts electrical energy into mechanical energy

  4. Converts mechanical energy into electrical energy
Reveal answer Fill a bubble to check yourself
D Correct answer
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.  

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

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.

  1. Will decrease

  2. Remains unchanged

  3. Will be doubled

  4. Will increase by a factor between 1 and 2
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

What is a commutator?

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.