Tag: electromagnetic induction

Quizzes (6) Questions (197)

Questions Related to electromagnetic induction

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

In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are 

  1. friction and windage losses

  2. copper losses

  3. hysteresis and eddy current losses

  4. none of the above

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

In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are hysteresis and eddy current losses The losses that can occur in a material are: Iron losses: Iron loss is caused by the alternating flux in the core and consists of hysteresis and eddy current losses. of coercivity on the curve. (The reversed magnetizing force has flipped enough of the domains so that the net flux within the material is zero.)

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

Eddy currents are produced in a metallic conductor when

  1. The magnetic flux linked with it changes

  2. It is placed in a changing magnetic field.

  3. It is placed in a magnetic field.

  4. Both A and B
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Eddy currents are produced when the magnetic flux passing through the metal object continuously changes. This may happen due to many reasons:
1) The object is placed in a region with changing magnetic field.
2) The object continuously moves in and out of the magnetic field region (may be uniform or non uniform).

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

A magnet is dropped down an infinitely long vertical copper tube

  1. The magnet moves with continuously increasing velocity and ultimately acquires a constant terminal velocity

  2. The magnet moves with continuously decreasing velocity and ultimately comes to rest

  3. The magnet moves with continuously increasing velocity but constant acceleration

  4. The magnet moves with continuously increasing velocity and acceleration
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As the magnet falls through the copper tube, changing magnetic flux induces eddy currents in the tube. According to Lenz's law, these eddy currents oppose the motion of the magnet, creating an upward magnetic force. Eventually, this magnetic drag balances gravity, and the magnet falls at a constant terminal velocity.

Multiple choice eddy currents motional emf electromagnetic induction electromagnetic induction and alternating currents physics
Which is the correct formula for calculating the power lost due to eddy currents per unit mass for a thin sheet or wire?? Where $P$ is the power lost per unit mass $(W/kg)$, $B _p$ is the peak magnetic field $(T)$, $d$ is the thickness of the sheet or diameter of the wire $(m)$, $f$ is the frequency $(Hz)$, $k$ is a constant equal to 1 for a thin sheet and 2 for a thin wire
  1. $P= \dfrac{{\pi}^2 {B _p}^2 d^2 f^2}{6k\rho D}$
  2. $P= \dfrac{{\pi}^2 {B _p}^2 d^2 f}{k\rho D}$
  3. $P= \dfrac{{\pi}^2 {B _p}^2 d^2 f^2}{6k\rho D^3}$
  4. $P= \dfrac{{\pi}^2 {B _p}^2 d^2 f}{6k\rho D^2}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

(A)$P=\dfrac { { \pi  }^{ 2 }{ B } _{ p  }^{ 2 }{ d }^{ 2 }{ f }^{ 2 } }{ 6k\rho D } \ m{ L }^{ 2 }{ T }^{ -3 }=\dfrac { \left( M{ T }^{ -2 }{ A }^{ -1 } \right) ^{ 2 }\left( { L }^{ 2 } \right) \left( { T }^{ -2 } \right)  }{ M{ L }^{ -3 } } \ m{ L }^{ 2 }{ T }^{ -3 }=M{ L }^{ 2 }{ T }^{ -3 }\ m{ L }^{ 2 }{ T }^{ -3 }\neq m{ L }^{ 2 }{ T }^{ -2 }$ where A = amphere, T = Time, L = Length ,M = mass.

similarly C and D not matches so option A is correct .

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

Eddy currents are used in

  1. electrolysis

  2. making a galvanometer dead beat

  3. electroplating

  4. to increase the sensitivity of galvanometer
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In general the coil of galvanometer oscillates about it's equilibrium due to rotational inertia which consumes some time. To avoid this coils is bound over  a metallic frame or plate oscillates in a magnetic field the eddy currents generated in the frame or plate oppose the motion and bring the frame to rest as the oscillations die out quickly. This is known as making galvanometer dead beat. 

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

The working of magnetic braking of trains is based on

  1. Steady current

  2. Eddy current

  3. Alternating current

  4. Pulsating current
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 It works the same as a disk eddy current brake, by inducing closed loops of eddy current in the conductive rail, which generate counter magnetic fields which oppose the motion of the train.

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

Read the following statements and answer whether the given statement is true or false.

Eddy current involves loss of energy in the form of heat.

  1. True

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

Eddy currents (also called Foucault currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor due to Faraday's law of induction. 

Eddy current involves loss of energy in the form of heat. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. They can be induced within nearby stationary conductors by a time-varying magnetic field created by an AC electromagnet or transformer. 
The statement is true.

Multiple choice physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

A square loop of side 12 cm and resistance 0.60$\Omega$ is placed vertically in the east-west plane. A uniform magnetic field of 0.1 T is setup across the plane in north-east direction. The magnetic field is decreased to zero in 0.6 s at a steady rate. The magnitude of current during this time interval is

  1. $1.42 \times 10^{-3} A$
  2. $2.67 \times 10^{-3} A$
  3. $3.41\times 10^{-3} A$
  4. $4.21 \times 10^{-3} A$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Here, Area $A=l^2=(12cm)^2=1.4\times 10^{-2} m^2$
$R=0.60\omega, B _1=0.10 T,\theta=45^0$
$B _2=0,dt=0.6$ s
Initial flux,
$\phi _1=B _1Acos\theta$
      $=0.10\times1.4\times10^{-2}\times cos 45^0$
      $=9.8\times 10^{-4}$

final flux, $\phi _2$=0
Induced emf,$E=\dfrac{| d\phi |}{dt}=\dfrac{|\phi _2-\phi _1|}{dt}$
                      $E=\dfrac{|9.8\times 10^{-4}|}{0.6}s\\,\,\,\,\,=1.6\times10^{-3}V$
Current, $I=\dfrac{E}{R}=\dfrac{1.6\times\times 10^{-3}}{0.6}=2.67 \times 10^{-3}$

Multiple choice physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

When the normal to a coil points in the direction of magnetic field (B), then flux is 

  1. a scalar quantity

  2. a vector quantity

  3. neither scalar nor vector

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

Dot product of field and area vectors is flux . $\Phi=B.dS$, and we know dot product of two vectors is a scalar quantity.
Therefore, flux is scalar.