Magnetic Effects of Electric Current Test

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Magnetic Effects of Electric Current Test - 41

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Question 1
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A boy was making a model of an electric bell. He connected the coil in the circuit and switched it on. However, the magnetism produced in the coil was not strong enough. He made some changes in the coil and the circuit was now working.
What changes did the boy make in the coil?

A
Decrease in the no. of turns in the coil

B
Replaced the coil

C
Increase in the number of turns in the coil

D
All of the above

Solution

If we increase the number of turns, the current flowing through it also increases. The magnetic field produced by a current-carrying wire at a given point depends directly on the current passing through it.
Question 2
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Which of the following figures correctly depicts the direction of magnetic field of a current carrying through a circular loop.

A

B

C

D

Solution

A magnetic field is produced by an electric current flowing through a circular coil of wire. Each small section of current carrying wire contributes to magnetic field lines. At the centre of circular wire, field lines become straight and perpendicular to the plane of coil.
Question 3
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A boy was making a model of electric bell. He connected the coil in the circuit and switched it on. However, the magnetism produced in the coil was not strong enough. He made some changes in the coil and the circuit was now working.
How can you produce strong magnetism without changing the magnet?

A
Change the Magnet

B
Increase the magnitude of current passing through the coil

C
Decrease the no of turns in the coil.

D
None of the above.

Solution

The magnetic effect of current produced is directly proportional to the current in wires due to which this effect is produced.

Hence by increasing the magnitude of current passing through the coil magnetism is increased.
Question 4
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Among the following components of electric motor, which component acts as a commutator?

A
Axle

B
Magnets

C
Brushes

D
Split Rings

Solution

A commutator is a rotary electrical switch in certain types of electric motors and electrical generators that periodically reverses the current direction between the rotor and the external circuit. It consists of a cylinder composed of multiple metal contact segments on the rotating armature of the machine.
Question 5
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What happens to the strength of the magnetic field if the number of turns is increased?

A
Strength of magnetic field increases

B
There is no change in the magnetic field

C
Strength of magnetic field decreases

D
Magnetic field disappears

Solution

The magnetic field produced by a current-carrying wire at a given point depends directly on the current passing through it. Therefore, if there is a circular coil having $$n$$ turns, the field produced is $$n$$ times as large as that produced by a single turn. This is because the current in each circular turn has the same direction and the field due to each turn then just adds up.
Question 6
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The speed of the motor can be increased by:

A
Decreasing the current

B
Increasing the number of turns in the coil

C
Increasing the size of motor

D
All of the above

Solution

The speed of the motor can be increased by increasing the number of turns in the coil.
If we increase the number of turns, the current flowing through it also increases. The magnetic field produced by a current-carrying wire at a given point depends directly on the current passing through it.
Question 7
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Why is an armature used in electric motor?

A
It enhances magnetic field

B
It enhances electric current

C
It enhances power of motor

D
It enhances speed

Solution

The combination of soft iron core and coil is called an armature. It is a rectangular iron core wrapped by the copper coil in a motor through which electricity passes and due to magnetic field it experiences a force and rotates and generates mechanical power.It enhances the power of motor.
Question 8
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In electric motor, which rule is used to find the direction of force on a current carrying conductor in a magnetic field?

A
Electromagnetic induction

B
Right-hand thumb rule

C
Fleming's left-hand rule

D
None of these

Solution

In an electric motor, the direction of the force on a current-carrying conductor in a magnetic field is determined by Fleming's left-hand rule.
According to Fleming’s left-hand rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of the magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.
Question 9
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What would happen to the direction of rotation of the motor, if the current were reversed.

A
direction of the rotation will be changed by 90 degree

B
direction of the rotation will be changed by 270 degree

C
direction of the rotation would be reversed.

D
direction of rotation would remain unchanged.

Solution
Question 10
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Which rule is used to find the direction of the induced current?

A
Fleming's right hand rule

B
Right hand thumb rule

C
Fleming's left hand rule

D
None of the above

Solution

Fleming's right-hand rule shows the direction of induced current when a conductor attached to a circuit moves in a magnetic field. It can be used to determine the direction of current in a generator's windings.