The disc of an instrument using eddy current damping should be of

A semicircular disc rests on a horizontal surface with its top flat surface horizontal and circular portion touching down. The coefficient of friction between semi circular disc and horizontal surface is µ. This disc is to be pulled by a horizontal force applied at one edge and it always remains horizontal. When the disc is about to start moving, its top horizontal force will

A

Remain horizontal

B

Slant up towards direction of pull

C

Slant down towards direction of pull

D

None of the above

A disc is a spinning with an angular velocity $$\omega $$ rad/s about the axis of spin. The couple applied to the disc causing precession will be (where $$I$$ = Mass moment of inertia of the disc and $$\omega {\text{P}}$$ = Angular velocity of precession of the axis of spin)

A

$$\frac{1}{2}I{\omega ^2}$$

B

$$I{\omega ^2}$$

C

$$\frac{1}{2}I\omega \omega {\text{P}}$$

D

$$I\omega \omega {\text{P}}$$

The moment of inertia of a thin disc of mass ‘m’ and radius ‘r’, about an axis through its center of gravity and perpendicular to the plane of the disc is

A

$$\frac{{{\text{m}}{{\text{r}}^2}}}{2}$$

B

$$\frac{{{\text{m}}{{\text{r}}^2}}}{4}$$

C

$$\frac{{{\text{m}}{{\text{r}}^2}}}{6}$$

D

$$\frac{{{\text{m}}{{\text{r}}^2}}}{8}$$

A circular disc rotates at n rpm. The angular velocity of a circular ring of same mass and radius as the disc and to have the same angular momentum is

A

n rpm

B

$$\frac{{\text{n}}}{2}$$ rpm

C

$$\frac{{\text{n}}}{4}$$ rpm

D

2n rpm

No eddy current and hysteresis losses occur in

A

Electrostatic instruments

B

PMMC instruments

C

Moving iron instruments

D

Electrodynamo meter instruments

Which of the fpllowing inductor will have the least eddy current losses ?

A

Air core

B

Laminated iron core

C

Iron core

D

Powdered iron core

Which of the following inductor will have the least eddy current losses?

A

Air core

B

Laminated iron core

C

Iron core

D

Powdered iron core

A laminated iron core has reduced eddy-current losses because

A

More wire can be used with less D.C. resistance in coil

B

The laminations are insulated from each other

C

The magnetic flux is concentrated in the air gap of the core

D

The laminations are stacked vertically

A ferrite core has less eddy current loss than an iron core because

A

Ferrites have high resistance

B

Ferrites are magnetic

C

Ferrites have low permeability

D

Ferrites have high hysteresis

Which of the following is an advantage of eddy current heating?

A

The amount of heat generated can be controlled accurately

B

Heat at very high rate can be generated

C

The area of the surface over which heat is produced can be accurately controlled

D

All of the above

The disc of an instrument using eddy current damping should be of

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