Tag: physics

Questions Related to physics

Dynamo produces:

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

  1. Charge

  2. Electromotive force

  3. Electric field

  4. Magnetic field

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Correct Option: B
Explanation:

A dynamo is an electrical generator that produces direct current or (Electromotive force) with the use of a commutator.

A dynamo converts

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

  1. mechanical energy into sound energy

  2. mechanical energy into electrical energy

  3. electrical energy into mechanical energy

  4. electrical energy into sound energy

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Correct Option: B
Explanation:

Dynamo is an electric generator where shaft is rotated mechanically and electric energy is produced. It converts the mechanical motion of the driven shaft into electrical motion,with the aid of a magnet.

When speed of a DC generator decreases, the armature current 

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

  1. increases

  2. decreases

  3. does not change

  4. increases and decreases continuously

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Correct Option: A
Explanation:

The armature current will increase if the speed of the DC generator start decreasing due to an increase in voltage drop at armature resistance.

Dynamo is designed on the principle of 

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

  1. Electromagnetic induction

  2. Self induction

  3. Mutual induction

  4. Pascal's law

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Correct Option: A

The main difference between A.C. generator and D.C. generator is

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. carbon brushes

  2. magnets

  3. coil

  4. commutator

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Correct Option: A
Explanation:

The main difference  between $A.C$ generator and $D.C$ generator is carbon brushes.

A six pole generator with fixed field excitation develops an emf of $100 { V } ,$ when operating at 1500$ { rm }$ At what speed must it rotate to develop $120 { V } ?$ 

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

  1. $1200\mathrm { rpm }$

  2. $1800\mathrm { rpm }$

  3. $1500\mathrm { rpm }$

  4. $400\mathrm { rpm }$

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Correct Option: B

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. 

Which instrument works on the principle of "Electromagnetic induction?

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. Electric motor

  2. Fuse

  3. Electric bell

  4. Electric generator

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Correct Option: D

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.