Magnetic Effects of Electric Current Test

Result

Magnetic Effects of Electric Current Test - 13

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Question 1
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The magnetic lines of force inside a bar magnet:

A
are from north-pole to south-pole of the magnet

B
do not exist

C
depend upon the area of cross-section of the bar magnet

D
are from south-pole to north-pole of the magnet.

Solution

The lines of magnetic field from a bar magnet form closed lines. By convention, the field direction is taken to be outward from the north pole and in to the south pole of the magnet.Inside a bar magnet its from south to north pole.
Question 2
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The strength of magnetic field inside a long current carrying straight solenoid is:

A
more at the ends than at the centre

B
minimum in the middle

C
same at all points

D
found to increase from one end to the other

Solution

Answer is C
A solenoid is a coil of wire designed to create a strong magnetic field inside the coil. By wrapping the same wire many times around a cylinder, the magnetic field due to the wires can become quite strong. The number of turns refers to the number of loops the solenoid has. More loops will bring about a stronger magnetic field.
The magnetic field inside a solenoid is proportional to both the applied current and the number of turns per unit length. There is no dependence on the diameter of the solenoid, and the field strength doesn't depend on the position inside the solenoid, i.e., the field inside is constant.
The magnetic field is nearly uniform field in the center, i.e. inside of a long solenoid and the field outside is weak and divergent.
Question 3
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In case of a bar magnet, lines of magnetic induction

A
start from the north pole and end at the south pole

B
run continuously through the bar magnet and outside

C
emerge in circular paths from the middle of the bar

D
are produced only at the north pole like rays of light from a bulb

Solution

Magnetic lines of force in a bar magnet are continuous forming closed loops as shown in the figure.
Outside the magnet, the lines run from north pole to south pole whereas oppositely inside.
Question 4
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If the current in a wire is directed east wards and it is kept in a magnetic field directed northwards, the direction of force on the wire is:

A
due west

B
due south

C
vertically upwards

D
vertically downwards

Solution

By fleming's left hand rule, if current (middle finger) is directed eastwards and magnetic field (index finger) is directed northwards, then the net force (thumb) is directed vertically upwards.
Question 5
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Magnetic lines of force due to a long straight conductor carrying current are

A
straight lines

B
elliptical

C
circular

D
parabolic

Solution

Magnetic lines of force are always closed loops.
Also, for straight current carrying conductor their strength depends only on radial distance. For a fixed radial distance, the magnitude of magnetic field from current carrying conductor is constant. This means, the magnetic lines of force are concentric circles as shown in figure.
Question 6
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An electron is moving towards east in a magnetic field acting vertically downwards. So the electron is deflected towards:

A
South

B
North

C
East

D
West

Solution

An electron is moving towards east in a magnetic field acting vertically downwards. So, the electron is deflected in a mutually perpendicular direction to magnetic field. Using Fleming's left hand rule it is in south direction .
Question 7
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In which form the field lines inside the infinite solenoid are present ?

A
Perpendicular straight lines

B
Circular lines

C
Ellipsoidal lines

D
Parallel straight lines

Solution

The field lines inside the infinite solenoid are in the form of parallel straight lines. Since it is a infinite one, one can't find a edge of it where the field lines can bend.
Question 8
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Complete the following statements with an appropriate word / term to be filled in the blank space(s).

Magnetic field lines emerge from the _________ pole of a solenoid or a permanent magnet.

A
north

B
south

C
north-east

D
none of these

Solution

Magnetic field lines emerge from the north pole of a solenoid or a permanent magnet in the outside region of the magnet and it ends at the south pole.
Question 9
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The magnetic field generated along the axis of a solenoid is proportional to:

A
Its length

B
Square of current flowing in it

C
Number of turns per unit length in it

D
Reciprocal of its radius

Solution

The magnetic field generated along the axis of a solenoid is proportional to the number of turns per unit length in it.
Question 10
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An electric motor converts :

A
Electrical energy to light energy

B
Electrical energy to mechanical energy

C
Light energy to electrical energy

D
Mechanical energy to electrical energy

Solution

In an electrical motor, electrical energy is converted into mechanical energy.