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NCERT Exemplar Solution for CBSE Class 10 Science: Magnetic Effects of Electric Current (Part-I)

Jun 5, 2017 15:20 IST

    Class 10 Science NCERT Exemplar Problems, Magnetic Effects of Electric Current ncert exemplarHere you get the CBSE Class 10 Science chapter 13, Magnetic Effects of Electric Current: NCERT Exemplar Problems and Solutions (Part-I). This part of the chapter includes solutions for Question No. 1 to 12 from the NCERT Exemplar Problems for Class 10 Science Chapter: Magnetic Effects of Electric Current. These questions include only the Multiple Choice Questions (MCQs) framed from various important topics in the chapter. Each question is provided with a detailed explanation.

    CBSE Class 10 Science Syllabus 2017-2018

    NCERT Exemplar problems are a very good resource for preparing the critical questions like Higher Order Thinking Skill (HOTS) questions. All these questions are very important to prepare for CBSE Class 10 Science Board Examination 2017-2018 as well as other competitive exams.

    Find below the NCERT Exemplar problems and their solutions for Class 10 Science Chapter, Magnetic Effects of Electric Current:

    Multiple Choice Questions (MCQs)

    Question1. 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)

    Explanation: Parallel and equidistant magnetic field lines represent uniform and constant field strength.

    Question 2. If the key in the arrangement as shown below is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are

    Magnetic Effects of Electric Current MCQs

    (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. (c)

    Explanation: If key is taken out then current will stop and no magnetic field exists due to the conductor. Thererfore, at the point O, there will be earth’s magnetic field and they will be straight lines parallel to each other.

    NCERT Solutions for CBSE Class 10 Science

    Question 3. 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

    Magnetic Effects of Electric Current NCERT Exemplar Problems

    (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)

    Explanation: When we see from point A, the direction of current will be anticlockwise and when we see the direction of current from point B then it will be clockwise. It means current is flowing as shown in the figure given below.

    By right-hand thumb rule, the magnetic field lines will enter from point B and come out from point A.

    We also know that, the magnetic field lines emerge from North Pole and merge at the South Pole outside the magnet.

    Hence, in this circuit face A represents North pole and face B represents south pole.

    Question 4. 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)

    Explanation: Option (a), (b) and (d) are correct. Only option (c) is incorrect because the pattern of magnetic fields due to solenoid and bar magnet is almost same.

    Solenoid Magnetic Field Lines

    Question 5. A uniform magnetic field exists in the plane of paper pointing from left to right as shown in figure. In the field an electron and a proton move as shown. The electron and the proton experience.

    Electron Proton Movement in Magnetic Field Lines

    (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 respectively

    Answer. (a)

    Explanation: Direction of current is taken as opposite to the flow of electron or in the direction of flow of protons.

    In the given figure, the proton and electron are moving in opposite direction to each other and in perpendicular to the direction of magnetic field. So, current due to both electron and proton are in same direction. Hence, the forces acting on both will be in the same direction. By Fleming's left hand rule the direction force is pointing into the plane of paper.

    Question 6. 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.  (c)

    Explanation: An electric motor is a device that converts electric energy into mechanical energy.

    An electric motor has an electromagnet in instead of permanent magnet (as permanent magnet does not produce strong magnetic field).

    Large number of turns of the conducting wire in the current-carrying coil to produce stronger magnetic field.

    It also has a soft iron core on which the coil is wound also known as armature.

    Question 7. In the arrangement shown in 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

    Magnetic Effects of Electric Current MCQs

    (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 galvanometers deflections that die out shortly, the deflections are in the same direction.

    (d) There are momentary galvanometers deflections that die out shortly, the deflections are in opposite directions. Thus the galvanometer shows momentary deflections in opposite directions.

    Answer. (d)

    Explanation: As the current in the first coil changes, the magnetic field associated with it also changes. Thus the magnetic field lines around the other coil also change. Hence the change in magnetic field lines associated with the secondary coil is the cause of induced electric current in it by the process of electromagnetic induction. Due to this reason, a momentary deflection in galvanometer will be observed which will die out soon when the current flowing through first coil attains steady state.

    Due to similar phenomenon, a momentary deflection is again observed in opposite direction when key is removed as in this case current is decreasing in the circuit.

    Question 8. 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, where as the alternating current reverses its direction periodically.

    (d) In India, the AC changes direction after every1/50 second.

    Answer. (d)

    Explanation: Here option (a), (b) and (c) are knowledge based options and are correct.

    Option (d) is incorrect because the frequency of 'AC' in India is 50 cycle/s. So, time period of AC is 1/50 s. We know that, AC changes its direction after every half time period, i.e., 1/ (2 × 50) or1/100 s.  So, in India the AC changes direction after every 1/100 s.

    Question 9. A constant current flows in a horizontal wire in the plane of the paper from east to west as shown in figure. The direction of magnetic field at a point will be north to south.

    Magnetic Effect of Electric Current NCERT Exemplar Problems

    (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)

    Explanation: If we observe the direction of magnetic field by applying right hand thumb rule then, we will find that the direction of magnetic field is from North to South below the wire.

    Question 10 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)

    Explanation: Inside the solenoid, magnetic field lines are parallel to each other hence forming a uniform field strength which indicates that the magnetic field is the same at all points inside the solenoid.

     Magnetic Field Lines Through a Solenoid

    Question 11. 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)

    Explanation: AC generator has slip rings while the DC generator has a split ring type commutator. To convert an AC generator into DC generator the split ring type commutator with which unidirectional current is obtained.

    Question 12. 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)

    Explanation: Use of electric fuse is the most important method used for protecting home appliances from short circuiting or overloading.

    Generally, thin wire with low melting having specific rating is connected in series with the electric devices. When the current passing through the fuse exceeds a specific value then by heating effect of current it melts and breaks the circuit.

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