Tag: motional emf

Questions Related to motional emf

A  $1\mathrm { m }$  long conducting rod rotates with an angular frequency of  $400\mathrm { rad } \mathrm { s } ^ { - 1 }$  about an axis normal to the rod passing through its one end. The other end of the rod is in contact with a circular metallic ring. A constant magnetic field of  $0.5\mathrm { T }$  parallel to the axis exists everywhere.Calculate the e.m.f developed between the center and the ring?

motional emf physics

  1. $100 \mathrm { V }$

  2. $101 \mathrm { V }$

  3. $102 \mathrm { V }$

  4. $103 \mathrm { V }$

Show answer
Correct Option: A

A charged particle enters in a uniform magnetic field with velocity at an angle of ${ 60 }^{ o }$ with the magnetic field. The pitch of helical path is x, the radius of helix is 

motional emf physics

  1. $\dfrac { x }{ 2\sqrt { 3 } x } $

  2. $\dfrac { 2x }{ \sqrt { 3 } \pi } $

  3. $\dfrac { \sqrt { 3 } x }{ \pi } $

  4. $\dfrac { \sqrt { 3 } x }{ 2\pi } $

Show answer
Correct Option: D

When a charged particle is projected perpendicular to a magnetic field then the

motional emf physics

  1. Velocity of the particle remain constant

  2. Momentum of the particle remain constant

  3. Kinetic energy of the particle remain constant

  4. Path of particle is straight line

Show answer
Correct Option: C

A $0.1m$ long conductor carrying a current of $50A$ is perpendicular to a magnetic field of $1.21mT$. The mechanical power to move the conductor with a speed of $1m{s}^{-1}$ is

motional emf physics

  1. $0.25mW$

  2. $6.25mW$

  3. $0.625W$

  4. $1W$

Show answer
Correct Option: B
Explanation:

Mechanical power required $=$ electrical power expended due to the induced emf 

                                               $= (Blv) \times I \ =( 0.00121 \times 0.1 \times 1 ) \times 50\ =6.25 m W $

A non conducting ring having charge q uniformly distributed over its circumference is placed on a rough horizontal surface. A vertical time varying magnetic field $B=4t^2$ is switched on a time $t=0$. Mass of the ring is m and radius is R. The ring starts rotating after $2$ seconds. The coefficient of friction between the ring and the tablets.

motional emf physics

  1. $\displaystyle\frac{4qmR}{g}$

  2. $\displaystyle\frac{2qmR}{g}$

  3. $\displaystyle\frac{8qR}{mg}$

  4. $\displaystyle\frac{qR}{2mg}$

Show answer
Correct Option: C

Which of the following does not use the application of eddy current?

eddy currents motional emf electromagnetic induction electromagnetic induction and alternating currents physics

  1. Electric power meters

  2. Induction furnace

  3. LED lights

  4. Magnetic breaks in trains

Show answer
Correct Option: C
Explanation:

C. LED light.

Because in the given option, Electric power meter, Induction furnace, and magnetic break in trains are the application of eddy current.

Induction Furnace make use of :

eddy currents motional emf electromagnetic induction electromagnetic induction and alternating currents physics

  1. Self induction

  2. Mutual induction

  3. eddy current

  4. none of these

Show answer
Correct Option: C
Explanation:

Inductance Furnace makes use of Eddy current. 

Identify the wrong statement

eddy currents motional emf electromagnetic induction electromagnetic induction and alternating currents physics

  1. Eddy currents are produced in a steady magnetic field

  2. Eddy currents can be minimized by using laminated core

  3. Induction furnace uses eddy current to produce heat

  4. Eddy current can be used to produce breaking force in moving trains

Show answer
Correct Option: A
Explanation:

Eddy currents comes in picture only when there is change in linked magnetic flux. 

They can be created when a conductor is moving through a magnetic field, or when the magnetic field surrounding a stationary conductor is varying i.e. anything which results in the conductor experiencing a change in the intensity or direction of a magnetic field can produce eddy currents.

Thus  $A$ is the correct option.

Identify the wrong statement.

eddy currents motional emf electromagnetic induction electromagnetic induction and alternating currents physics

  1. Eddy currents are produced in a steady magnetic field.

  2. Eddy currents can be minimized by using laminated core.

  3. Induction furnace uses eddy current to produce heat.

  4. Eddy current can be used to produce breaking force in moving trains.

Show answer
Correct Option: A
Explanation:

Eddy currents comes in picture only when there is change in linked magnetic flux. Thus statement A is wrong.

Which of the following law follows when eddy currents are generated?

eddy currents motional emf electromagnetic induction electromagnetic induction and alternating currents physics

  1. Lenz's law

  2. Gauss's law

  3. Both A and B

  4. None of these

Show answer
Correct Option: A
Explanation:

Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field.By Lenz's law, an eddy current creates a magnetic field that opposes the change in the magnetic field that created it, and thus eddy currents react back on the source of the magnetic field.Lenz law, the current swirls in such a way as to create a magnetic field opposing the change; for this to occur in a conductor, electrons swirl in a plane perpendicular to the magnetic field.

Image result for law follows when eddy currents are generated