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Question (11)

QN001851

If the direction of current in an electromagnet is reversed, then

(A) its poles reverse
(B) its size changes
(C) it stops working permanently
(D) current stops automatically

Correct Answer: A

Explanation:

Reversing current reverses magnetic poles.

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Question (12)

QN001852

An electromagnet has end A as North pole. After reversing battery terminals, end A will become

(A) North pole again
(B) South pole
(C) neutral
(D) non-magnetic iron

Correct Answer: B

Explanation:

Reversing current changes North pole into South pole.

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Question (13)

QN001853

A current carrying wire is placed above a compass needle. If the switch is opened, the needle

(A) rotates continuously
(B) points randomly
(C) returns to original direction
(D) gets demagnetised

Correct Answer: C

Explanation:

Compass returns to original position when current stops.

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Question (14)

QN001854

Which of the following devices works mainly on the magnetic effect of electric current?

(A) Electric iron
(B) Electric kettle
(C) Lifting electromagnet
(D) Immersion rod

Correct Answer: C

Explanation:

Lifting electromagnets use magnetic effect of current.

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Question (15)

QN001855

Why are lifting electromagnets useful in scrap yards?

(A) They can lift only plastic objects
(B) They can switch magnetism ON and OFF
(C) They work without electricity
(D) They permanently magnetise all metals

Correct Answer: B

Explanation:

Electromagnets can be controlled by switching current ON and OFF.

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Question (16)

QN001856

A crane operator switches OFF the current in a lifting electromagnet. What happens immediately?

(A) Magnetic field increases
(B) Iron objects fall off
(C) Iron becomes permanently magnetic
(D) Coil starts glowing

Correct Answer: B

Explanation:

Magnetic field disappears when current is switched OFF.

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Question (17)

QN001857

A student removes the iron nail from an electromagnet coil but current still flows. What will happen?

(A) Coil loses all magnetic effect
(B) Coil still acts like a weak magnet
(C) Coil becomes insulator
(D) Compass needle breaks

Correct Answer: B

Explanation:

Current carrying coil still acts as magnet without iron core.

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Question (18)

QN001858

The heating effect of electric current is caused because conductors offer

(A) reflection
(B) resistance
(C) transparency
(D) magnetism

Correct Answer: B

Explanation:

Resistance converts electrical energy into heat.

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Question (19)

QN001859

Nichrome wire becomes warm when current flows through it because it has

(A) low resistance
(B) very high melting point only
(C) higher resistance than copper
(D) no free electrons

Correct Answer: C

Explanation:

Nichrome offers higher resistance and produces more heat.

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Question (20)

QN001860

A nichrome wire connected to two cells becomes hotter than with one cell because

(A) wire length increases
(B) current becomes larger
(C) resistance becomes zero
(D) nichrome changes to copper

Correct Answer: B

Explanation:

Greater current produces more heat.

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Question (11)

If the direction of current in an electromagnet is reversed, then

Explanation:

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Question (12)

An electromagnet has end A as North pole. After reversing battery terminals, end A will become

Explanation:

Link:

Question (13)

A current carrying wire is placed above a compass needle. If the switch is opened, the needle

Explanation:

Link:

Question (14)

Which of the following devices works mainly on the magnetic effect of electric current?

Explanation:

Link:

Question (15)

Why are lifting electromagnets useful in scrap yards?

Explanation:

Link:

Question (16)

A crane operator switches OFF the current in a lifting electromagnet. What happens immediately?

Explanation:

Link:

Question (17)

A student removes the iron nail from an electromagnet coil but current still flows. What will happen?

Explanation:

Link:

Question (18)

The heating effect of electric current is caused because conductors offer

Explanation:

Link:

Question (19)

Nichrome wire becomes warm when current flows through it because it has

Explanation:

Link:

Question (20)

A nichrome wire connected to two cells becomes hotter than with one cell because

Explanation:

Link:

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