Chapter 13. Magnetic Effects of Electric Current

Class 10 Science Chapter 13 Magnetic Effects of Electric Current Multiple Choice Questions and Answers :

Question : Which of the following correctly describes the magnetic field near a long straight wire?

(a) The field consists of straight lines perpendicular to the wire.

(b) The field consists of straight lines parallel to the wire.

(c) The field consists of radial lines originating from the wire.

(d) The field consists of concentric circles centred on the wire.

Answer :  (d) The field consists of concentric circles centred on the wire.

[ When a current flows through a long straight wire, the magnetic field around the wire forms concentric circles. The direction of the magnetic field lines can be determined using the right-hand rule: if you point your thumb in the direction of the current, the curling of your fingers shows the direction of the magnetic field lines around the wire.]

Question : The phenomenon of electromagnetic induction is

(a) the process of charging a body.

(b) the process of generating magnetic field due to a current passing through a coil.

(c) producing induced current in a coil due to relative motion between a magnet and the coil.

(d) the process of rotating a coil of an electric motor.
Answer : (c) producing induced current in a coil due to relative motion between a magnet and the coil.

Question : The device used for producing electric current is called a

(a) generator.

(b) galvanometer.

(c) ammeter.

(d) motor.

Answer :  (a) generator.

[ A generator is a device used to produce electric current by converting mechanical energy into electrical energy. It operates based on the principle of electromagnetic induction, where the relative motion between a coil and a magnetic field induces an electric current in the coil. Generators are commonly used to generate electricity in power plants and various other applications.]

4. The essential difference between an AC generator and a DC generator is that

(a) AC generator has an electromagnet while a DC generator has permanent magnet.

(b) DC generator will generate a higher voltage.

(c) AC generator will generate a higher voltage.

(d) AC generator has slip rings while the DC generator has a commutator.

Answer :  (d) AC generator has slip rings while the DC generator has a commutator.

[ The essential difference between an AC (alternating current) generator and a DC (direct current) generator lies in the method used to transfer the generated electricity from the rotating coil to the external circuit.]

5. At the time of short circuit, the current in the circuit

(a) reduces substantially.

(b) does not change.

(c) increases heavily.

(d) vary continuously.

Answer : (c) increases heavily.

[ During a short circuit, the low-resistance path causes a rapid surge in current, as there is little impedance to limit the flow. This can be dangerous and damaging.]

Question :  When electric current is passed through the coil of a solenoid, then the magnetic field [SEBA 2023]

(a) increase along the direction of current .

(b) decrease along the direction of current

(c) remains the same at all times

(d) becomes zero

Answer : (a) Increase along the direction of the current.

[ When an electric current is passed through the coil of a solenoid, the magnetic field around the solenoid increases along the direction of the current. ]

Question : In electric generator , energy converted from  energy to  energy . [SEBA 2023]

Answer : mechanical  ; electrical

Question :  Choose the incorrect statement from the following regarding magnetic lines of field

(a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points

(b) Magnetic field lines are closed curves

(c) If magnetic field lines are parallel and equidistant, they represent zero field strength

(d) Relative strength of magnetic field is shown by the degree of closeness of the field lines

Answer : (c) If magnetic field lines are parallel and equidistant, they represent zero field strength.

[ This is incorrect because parallel and equidistant field lines indicate uniform field strength, not zero field strength.]

Question :  If the key in the arrangement (Figure 13.1) 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

Answer : (a) concentric circles

[ The magnetic field lines over the horizontal plane ABCD would form concentric circles. This occurs when a current-carrying conductor is in the shape of a loop, creating a circular magnetic field pattern.]

Question :  A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is ON. The current as seen from points A and B (in the plane of paper and on the axis of the coil) is anti clockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the resultant magnet is on the face close to

(a) A

(b) B

(c) A if the current is small, and B if the current is large

(d) B if the current is small and A if the current is large

Answer : (a) A

[ The N-pole of the resultant magnet is on the face close to (a) A. This is because the direction of the magnetic field lines follows the right-hand thumb rule, and the N-pole is determined by the direction of current flow.]

Question :  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

Answer : (c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet.

[ This is incorrect. The magnetic field pattern inside a solenoid is similar to that around a bar magnet, with field lines running from the north pole to the south pole inside the solenoid. ]

Question :  A uniform magnetic field exists in the plane of paper pointing from left to right as shown in Figure 13.3. In the field an electron and a proton move as shown. The electron and the proton experience

(a) forces both pointing into the plane of paper

(b) forces both pointing out of the plane of paper

(c) forces pointing into the plane of paper and out of the plane of paper, respectively

(d) force pointing opposite and along the direction of the uniform magnetic field .

Answer : (d) force pointing opposite and along the direction of the uniform magnetic field.

[ The force experienced by a charged particle moving in a magnetic field is perpendicular to both the velocity of the particle and the direction of the magnetic field. ]

Question :  Commercial electric motors do not use

(a) an electromagnet to rotate the armature

(b) effectively large number of turns of conducting wire in the current carrying coil

(c) a permanent magnet to rotate the armature

(d) a soft iron core on which the coil is wound

Answer : (a) an electromagnet to rotate the armature.

[ Commercial electric motors typically use a permanent magnet or a combination of permanent magnets and soft iron cores, but they do not rely on an electromagnet to rotate the armature.]

Question :  In the arrangement shown in Figure 13.4 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 .

Answer : (d) There are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions.

[ When the key is inserted or removed, induced currents are produced in the coils, resulting in momentary galvanometer deflections in opposite directions.]

Question :  Choose the incorrect statement

(a) Fleming’s right-hand rule is a simple rule to know the direction of induced current

(b) The right-hand thumb rule is used to find the direction of magnetic fields due to current carrying conductors

(c) The difference between the direct and alternating currents is that the direct current always flows in one direction, whereas the alternating current reverses its direction periodically

(d) In India, the AC changes direction after every 150 second .

Answer : (d) In India, the AC changes direction after every 150 seconds.

[ This is incorrect. In India, as in many other places, the standard frequency of AC power is 50 hertz (Hz), which means it changes direction (alternates) 50 times per second, not every 150 seconds.]

Question :  A constant current flows in a horizontal wire in the plane of the paper from east to west as shown in Figure 13.5. The direction of magnetic field at a point will be North to South

   

(a) directly above the wire

(b) directly below the wire

(c) at a point located in the plane of the paper, on the north side of the wire

(d) at a point located in the plane of the paper, on the south side of the wire

Answer : (b) Directly below the wire.

[ The direction of the magnetic field due to a current in a wire is concentric circles around the wire. Directly below the wire, the magnetic field points from north to south. ]

Question :  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

Answer : (c) Same at all points.

[  In a long current-carrying straight solenoid, the magnetic field strength is uniform inside and the same at all points. ]

Question :  To convert an AC generator into DC generator

(a) split-ring type commutator must be used

(b) slip rings and brushes must be used

(c) a stronger magnetic field has to be used

(d) a rectangular wire loop has to be used

Answer : (a) Split-ring type commutator must be used.

[ To convert an AC generator into a DC generator, a split-ring commutator is employed. The commutator helps in changing the direction of the current in the coil, converting the alternating current to direct current.]

Question :  The most important safety method used for protecting home appliances from short circuiting or overloading is

(a) earthing

(b) use of fuse

(c) use of stabilizers

(d) use of electric meter

Answer : (b) Use of fuse.

[ The most important safety method for protecting home appliances from short-circuiting or overloading is the use of a fuse. A fuse interrupts the circuit if there is excessive current, preventing damage to the appliances and the wiring. ]