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

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

Invar tapes used for measuring base lines, is made of nickel-iron alloy containing nickel

A

24 %

B

36 %

C

40 %

D

60 %

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

A

Low, high

B

High, high

C

High, low

D

Low, low

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

Nickel percentage in invar which is an iron-nickel alloy, and is used as a thermocouple material is

A

12

B

36

C

54

D

68

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

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

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

Addition of __________ to the steel helps in increasing the residual magnetism in steel used for making magnets.

A

Chromium

B

Nickel

C

Tungsten

D

Cobalt

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

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