Those materials are well suited for making permanent magnets which have ________ retentivity and ________ coercivity.

Materials used for making permanent magnets containing iron and nickel are made by __________ technique.

A

Powder metallurgy

B

Casting

C

Forging

D

None of these

The materials having low retentivity are suitable for making

A

weak magnets

B

temporary magnets

C

permanent magnets

D

none of the above

Hard steel is suitable for making permanent magnets because

A

It has good residual magnetism

B

Its hysteresis loop has large area

C

Its mechanical strength is high

D

Its mechanical strength is low

Those magnetic materials are best suited for making armature and transformer cores which have ________permeability and _________hysteresis loss.

A

High, high

B

Low, high

C

High, low

D

Low, low

Permanent magnets are made of high carbon steel and

A

15% of cobalt

B

20% of cobalt

C

35% of cobalt

D

45% of cobalt

Alnico, an alloy used extensively for permanent magnets contains iron, nickel, aluminium and cobalt in the following ratio

A

50 : 20 : 20 : 10

B

40 : 30 : 20 : 10

C

50 : 20 : 10 : 20

D

30 : 20 : 30 : 20

Which of the following memories contains a thin film of magnetic material sandwitched between two permanent bias magnets?

A

ROM

B

Magnetic disk

C

Core memory

D

Bubble memory

E

None of the above

Permanent magnets are normally made of

A

Alnico alloys

B

Aluminium

C

Cast iron

D

Wrought iron

The use of permanent magnets is. not made in

A

magnetoes

B

energy meters

C

transformers

D

loud-speakers

Water retentivity for brick masonry should not be less than

A

50%

B

60%

C

70%

D

80%

Those materials are well suited for making permanent magnets which have retentivity and coercivity.

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