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

Eddy currents travel in

  1. closed paths.

  2. nonconductive materials.

  3. axially when testing rod with an encircling coil

  4. perpendicular to the test surface
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When there is a change in magnetic flux associated with a large piece of metal then currents are induced in that metal these currents are travelling in a closed circular path,  similar to Whirlpools or eddies in water. Such currents are known and Eddy Currents

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

Hysteresis loss and eddy current losses are used in

  1. induction heating of steel

  2. dielectric heating

  3. induction heating of brass

  4. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

There is a magnetic loss occur in ferromagnetic material like iron and steel in form of heat these losses are used for induction heating and cooking. For example $\rightarrow$ heating of transformer.

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

Which of the following is not an application of eddy currents.

  1. Induction heater

  2. Conductivity meters for non-magnetic metals

  3. Skin effect

  4. Coating Thickness Measurements
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Eddy currents are the currents induced in the body of a conductor when the amount of magnetic   flux linked with it changes
(i)    Induction furnace (heating effect of eddy current)
(ii)   Dead-beat galvanometer (electromagnetic damping)
(iii)  Electric brakes
(iv) Diathermy ( Strong 50 MHz A.C. passed through human body, also called deep heat treatment )
(v)  Induction motor
(vi) Car-speedometer
(vii)Energy meter
Multiple choice eddy currents motional emf electromagnetic induction electromagnetic induction and alternating currents physics

Silicon steel used in lamination mainly reduces

  1. Hysteresis loss

  2. Eddy current losses

  3. Copper loss

  4. All of the above 
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Silicon steel used in lamination mainly reducesHysteresis loss,Eddy current losses,Copper loss. In order to minimize the eddy currents more,magnetic core is laminated . The hysteresis coefficient of silicon steel is less, so hysteresis loss can be reduced. used mainly because of the following advantages: low hysteresis loss. low copper loss due to lower grain resistance.

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
B Correct answer
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. <span>$P= \dfrac{{\pi}^2 {B _p}^2 d^2 f}{k\rho D}$</span>

  3. <span>$P= \dfrac{{\pi}^2 {B _p}^2 d^2 f^2}{6k\rho D^3}$</span>

  4. <span>$P= \dfrac{{\pi}^2 {B _p}^2 d^2 f}{6k\rho D^2}$</span>
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.