Magnetic Effects of Electric Current Test

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Magnetic Effects of Electric Current Test - 21

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Question 1
1 / -0

Particles having positive charge occasionally come with high velocity from the sky towards the earth on account of magnetic field of earth, they would be deflected towards:

A
North

B
South

C
East

D
West

Solution

Using fleming's left hand rule, they will turn toward right i.e. east
Question 2
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The lines of force of a bar magnet are:

A
Parallel and straight

B
Concentric circles

C
Curved lines

D
Curved closed loops

Solution

Lines of force of bar magnet are closed curved loops as shown in the attached figure.
Question 3
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If the key in the arrangement is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are:

A
Concentric circles

B
Elliptical in shape

C
Straight lines parallel to each other

D
Concentric circles near the point O but of elliptical shapes as we go away from it

Solution

If the key in the arrangement is taken out (the circuit is made open) then there will be no current in the circuit that implies no magnetic field due to the circuit. So only the earth's magnetic field will be present in that region and the field due to it will be straight lines parallel to each other over the horizontal plane ABCD.
Question 4
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A long solenoid with closely spaced turns carries a direct electric current. Each turn of wire exerts:

A
an attractive force on the next adjacent turn.

B
a repulsive force on the next adjacent turn.

C
zero force on the next adjacent turn.

D
either an attractive or a repulsive force on the next adjacent turn, depending on the direction of current in the solenoid.
Question 5
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The laws of electromagnetic induction have been used in the construction of a :

A
Galvanometer

B
Voltmeter

C
Electric motor

D
Electric generator

Solution

The laws of electromagnetic induction have been used in the construction of an electric generator. In an electric generator, emf is induced by changing the flux.
A galvanometer is used to detect current. So, no use of electromagnetic induction.
The voltmeter is used to measure voltage. Again, no use of electromagnetic induction.
Electric motor changes electrical energy into mechanical energy, which has no use of laws of electromagnetic induction.
Question 6
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A proton is projected horizontally eastward in a uniform magnetic field, which is horizontal and southward in direction. The proton will be deflected

A
upward

B
downward

C
northward

D
southward

Solution

By Fleming's left hand rule, taking velocity (middle finger) in east direction and magnetic field (index finger) in south direction, we get force (thumb) in vertically downward direction.
Question 7
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The incorrect statement regarding the lines of force of the magnetic field B is:

A
magnetic intensity is a measure of lines of force passing through unit area held normal to it.

B
magnetic lines of force form a closed curve.

C
inside a magnet, its magnetic lines of force move from the north pole of a magnet towards its south pole.

D
magnetic lines of force never cut each other.

Solution

$$\rightarrow$$ Magnetic intensity is proportional to the number of magnetic field lines.
$$\rightarrow$$ Magnetic field lines of forces are closed curves.
$$\rightarrow$$ Inside the magnet, field lines move from the South Pole to the North Pole.
$$\rightarrow$$ Magnetic lines of force never cut each other.
Therefore, option C is incorrect
Question 8
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For a current in a long straight solenoid N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is:

A
the field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all points inside the solenoid

B
the strong magnetic field produced inside the solenoid can be used to magnetise a piece of magnetic material like soft iron, when placed inside the coil

C
the pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet

D
the N- and S-poles exchange position when the direction of current through the solenoid is reversed

Solution

The pattern of the magnetic field associated with the solenoid is exactly same as the pattern of the magnetic field around a bar magnet. It also has two poles on the two extreme end and the field lines are also looks same (figure).
Question 9
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In the arrangement shown in the figure, there are two coils wound on a non-conducting cylindrical rod. Initially, the key is not inserted. Then the key is inserted and later removed. Then :

A
the deflection in the galvanometer remains zero throughout

B
there is a momentary deflection in the galvanometer but it dies out shortly and there is no effect when the key is removed

C
there are momentary galvanometer deflections that die out shortly, the deflections are in the same direction

D
there are momentary galvanometer deflections that die out shortly, the deflections are in opposite directions

Solution

In the figure, two coils are not electrically connected to each other because they are wound on a non conducting rod. Say Coil-1 is connected across a battery through a key. This coil is called primary coil. Coil-2 is connected across a galvanometer. This coil is called secondary coil.
When the key is pressed it is observed that, the galvanometer shows a small momentary deflection and then returns to zero. When the key is released, the galvanometer again shows a small momentary deflection, but in opposite direction and then returns to zero. As the coil is connected to a non-conducting rod the self induced electromotive force or voltage is very less and thus the current that flows in one direction slowly diminishes and returns to zero. Similarly when the key is released the current flows in the opposite direction and slowly diminishes.
Thus, the rate of change of electromotive force (e.m.f.) in coil-1, decides the magnitude of deflection of galvanometer. The magnetic flux of primary coil is linked through the rod to the secondary coil. Thus, the induced e.m.f. or current is produced in a coil when varying current flows through a neighboring coil.
Question 10
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If the forefinger shows the direction of the magnetic field and the thumb indicates the motion of the conductor, then, according to Flemings left-hand rule, what does the middle finger point at?

A
The direction of e.m.f.

B
The direction of current

C
The direction of flux

D
The direction of lines of force