Tag: physics

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

A dynamo converts

  1. mechanical energy into sound energy

  2. mechanical energy into electrical energy

  3. electrical energy into mechanical energy

  4. electrical energy into sound energy
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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 $120 { V } ?$ 

  1. $1200\mathrm { rpm }$

  2. $1800\mathrm { rpm }$

  3. $1500\mathrm { rpm }$

  4. $400\mathrm { rpm }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For a generator with fixed field excitation, the induced EMF is directly proportional to the speed of rotation (E = k * N). Given 100V at 1500 rpm, the constant k is 100/1500. To find the speed for 120V, we solve 120 = (100/1500) * N, which yields N = 1800 rpm.

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

Which instrument works on the principle of "Electromagnetic induction?

  1. Electric motor

  2. Fuse

  3. Electric bell

  4. Electric generator
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

An electric generator converts mechanical energy into electrical energy based on Faraday's law of electromagnetic induction. An electric motor works on the force exerted on a current-carrying conductor in a magnetic field, while a fuse and bell operate on thermal and magnetic effects respectively.

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.