Tag: motional emf

Quizzes (0) Questions (43)

Questions Related to motional emf

Multiple choice motional emf physics

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?

  1. $100 \mathrm { V }$
  2. $101 \mathrm { V }$
  3. $102 \mathrm { V }$
  4. $103 \mathrm { V }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The emf induced in a rotating rod is E = (1/2) * B * omega * L^2. Substituting B = 0.5 T, omega = 400 rad/s, and L = 1 m, we get E = 0.5 * 0.5 * 400 * 1^2 = 100 V.

Multiple choice motional emf physics

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 

  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 } $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Pitch x = v * cos(theta) * T = v * cos(theta) * (2 * pi * m) / (q * B). Radius R = (m * v * sin(theta)) / (q * B). Dividing R by x gives R / x = (sin(theta)) / (2 * pi * cos(theta)) = tan(60) / (2 * pi) = sqrt(3) / (2 * pi). Thus R = (sqrt(3) * x) / (2 * pi).

Multiple choice motional emf physics

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

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

When a charged particle enters a magnetic field perpendicularly, the magnetic force acts perpendicular to the velocity. This force changes the direction of velocity but not its magnitude, meaning kinetic energy remains constant.

Multiple choice motional emf physics

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

  1. $0.25mW$
  2. $6.25mW$
  3. $0.625W$
  4. $1W$
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $

Multiple choice motional emf physics

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.

  1. $\displaystyle\frac{4qmR}{g}$
  2. $\displaystyle\frac{2qmR}{g}$
  3. $\displaystyle\frac{8qR}{mg}$
  4. $\displaystyle\frac{qR}{2mg}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice eddy currents motional emf electromagnetic induction electromagnetic induction and alternating currents physics

Identify the wrong statement

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

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

Identify the wrong statement.

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

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

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

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

  1. Lenz's law

  2. Gauss's law

  3. Both A and B

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
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