NCERT Exemplar for Class 10 Science Chapter 13 - Magnetic Effects of Electric Current (Book Solutions)

Multiple Choice Questions (MCQs)

1. 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

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

Explanation: When viewed from a distance, magnetic field lines appear to be parallel. This does not, however, imply that the field strength is zero. There would be no field line if the field strength is zero.

2. 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

Ans: (a) Concentric circles

Explanation: Magnetic field lines create concentric rings around a straight current carrying conductor.

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

(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

Ans: (a) A

Explanation: Magnetic field lines run from the south pole to the north pole. Because field lines are heading from B to A, point A represents the north pole.

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.

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

Explanation: A solenoid functions in the same way as a bar magnet does. As a result, the solenoid's magnetic field pattern is identical to the magnetic field pattern around a bar magnet.

5. 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 respectively

Ans: (a) forces both pointing into the plane of paper

Explanation: The inverse of the direction of electron movement is the direction of current. The current will rise as a result. The thumb is pointing into the paper if the index finger is pointing in the direction of the magnetic field and the ring finger is pointing in the direction of current.

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

Ans: (c) A permanent magnet to rotate the armature

Explanation: In commercial electric motors, electromagnets are utilised instead of permanent magnets.

7. In the arrangement shown in Figure 13.4 there are two coils wound on a nonconducting 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

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

Explanation: Galvanometer exhibits brief deflection in one direction when key is inserted. The galvanometer exhibits a transient deflection in the opposite direction when the key is withdrawn.

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, whereas the alternating current reverses its direction

periodically

(d) In India, the AC changes direction after every 1/50 second

Ans: (d) In India, the AC changes direction after every 1/50 second

Explanation: Every 1/100 second, the AC in India reverses direction.

9. 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

Ans: (b) directly below the wire

Explanation: A straight conductor carrying current from E to W is depicted by line WE. When viewed from the east, the magnetic field lines look clockwise, i.e. S to N above the wire and N to S below the wire. This is the situation, according to the Right Hand Thumb Rule.

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

Ans: (c) Same at all points

Explanation: Inside the solenoid, magnetic field lines are straight and parallel. This suggests that there is a significant magnetic field present. As a result, the magnetic field inside the solenoid is constant.

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

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

Explanation: After each half turn of the armature, the current is reversed via a split ring commutator. This keeps a DC current flowing.

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

Ans: (b) Use of fuse

Short Answer Questions

13. A magnetic compass needle is placed in the plane of paper near point A as shown in Figure 13.6. In which plane should a straight current-carrying conductor be placed so that it passes through A and there is no change in the deflection of the compass? Under what condition is the deflection maximum and why?

Ans: Within the plane of the paper. The compass's axis is vertical, and the conductor's field is also vertical. It might cause the compass needle to dip, which is not feasible in this circumstance (dips result only if the axis of the compass is horizontal). When the conductor via A is perpendicular to the plane of the paper, the deflection is greatest, and the field owing to it is greatest in the plane of the paper.

14. Under what conditions permanent electromagnet is obtained if a current carrying solenoid is used? Support your answer with the help of a labelled circuit diagram.

Ans: Following conditions are necessary for making electromagnet from a current carrying

solenoid.

(a) Circuit should be closed.

(b) A core of soft iron should be used.

15. AB is a current carrying conductor in the plane of the paper as shown in Figure 13.7. What are the directions of magnetic fields produced by it at points P and Q? Given r1 > r2, where will the strength of the magnetic field be larger?

Ans: If all of the fingers of the right hand are wrapped in a fist and the thumb displays the direction of electric current, then the direction of wrapped fingers reveals the direction of magnetic field, according to the Right Hand Thumb Rule. In the case of r1, the magnetic field is directed towards the paper. The magnetic field direction is out of the paper in the case of r2. The magnetic field strength at P is smaller than that at Q because r1 > r2.

16. A magnetic compass shows a deflection when placed near a current carrying wire. How will the deflection of the compass get affected if the current in the wire is increased? Support your answer with a reason.

Ans: The deflection gets stronger. The magnitude of current flowing through a straight conductor determines the intensity of the magnetic field.

17. It is established that an electric current through a metallic conductor produces a magnetic field around it. Is there a similar magnetic field produced around a thin beam of moving (i) alpha particles, (ii) neutrons? Justify your answer.

Ans: (i) Yes, Alpha particles being positively charged constitutes a current in the direction of motion.

(ii) No. The neutrons being electrically neutral constitute no current.

18. What does the direction of thumb indicate in the right-hand thumb rule? In what way this rule is different from Fleming’s left-hand rule?

Ans: The Fleming's left-hand rule describes the direction of force experienced by a current carrying conductor placed in an external magnetic field, whereas the thumb shows the direction of current in the straight conductor held by curled fingers.

19. Meena draws magnetic field lines of field close to the axis of a current carrying circular loop. As she moves away from the centre of the circular loop she observes that the lines keep on diverging. How will you explain her observation?

Ans: The magnetic field's strength reduces as the distance between them grows. The reduction in the degree of closeness of the lines of field indicates this.

20. What does the divergence of magnetic field lines near the ends of a current carrying straight solenoid indicate?

Ans: The divergence, or decreasing degree of closeness of magnetic field lines, shows a decrease in magnetic field intensity toward and beyond the solenoid's ends.

21. Name four appliances wherein an electric motor, a rotating device that converts electrical energy to mechanical energy, is used as an important component. In what respect motors are different from generators?

Ans: Electric fans, mixers, washing machines, and computer drives are just a few examples. Electrical energy is converted into mechanical energy by motors, whereas mechanical energy is converted into electrical energy by generators.

22. What is the role of the two conducting stationary brushes in a simple electric motor?

Ans: The brushes are linked to the battery and touch the outer surfaces of the split ring's two parts, which are insulated and fastened to the axle.

23. What is the difference between a direct current and an alternating current? How many times does AC used in India change direction in one second?

Ans: In AC, the current direction is always shifting. In DC, however, the current flow direction is always the same. The direction of the AC in India varies 100 times each second.

24. What is the role of fuse, used in series with any electrical appliance? Why should a fuse with defined rating not be replaced by one with a larger rating?

Ans: A fuse is a device that protects appliances against short-circuiting or overload. The fuse is rated for a specified maximum current and will blow if the current flowing through it exceeds the rated amount. When a fuse is changed with one with a higher rating, the appliances may be destroyed while the protective fuse remains lit. This technique of employing a fuse with an incorrect rating should be avoided at all costs.

Long Answer Questions

25. Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current-carrying loop is brought near it. Describe some salient features of magnetic lines of field concept.

Ans: Both current carrying loops and bar magnets have their own magnetic field lines. This causes a deviation in the earth's magnetic field, which already exists. The magnetic field has both a magnitude and a direction. The magnetic field lines from the N-pole enter the S-pole. The degree of closeness of the field lines represents the magnetic field intensity diagrammatically. Field lines cannot cross because two values of a net field cannot exist at the same time. There can only be one value, a unique net value. If the lines of a field in a particular location are parallel and evenly spaced, the field is said to be uniform.

26. With the help of a labeled circuit diagram illustrating the pattern of field lines of the magnetic field around a current-carrying straight long conducting wire. How is the right-hand thumb rule useful to find the direction of the magnetic field associated with a current-carrying conductor?

Ans: According to the right-hand thumb rule, if a current-carrying straight conductor is held in the right hand with the thumb pointing in the direction of the current, the fingers will wrap around the conductor in the direction of the magnetic field lines.

27. Explain with the help of a labeled diagram the distribution of magnetic field due to a current through a circular loop. Why is it that if a current-carrying coil has n turns the field produced at any point is n times as large as that produced by a single turn?

Ans: The Right-Hand Thumb Rule is also followed in a current-carrying circular loop.
This indicates the presence of magnetic field lines surrounding the conducting wire. The circular shape of the conductor, on the other hand, causes field lines at different positions of the loop to seem to form a ring around the loop's periphery. Many little rings looping around the edge of a large ring can be viewed.

Effect of Number of turns in a coil: If the number of turns in the coil is increased, then magnetic fields also increase. Due to this, the strength of the magnetic field increases with an increased number of turns in a coil.

28. Describe the activity that shows that a current-carrying conductor experiences a force perpendicular to its length and the external magnetic field. How does Fleming’s left-hand rule help us to find the direction of the force acting on the current-carrying conductor?

Ans: Using two connecting wires, suspend a tiny rod (AB) of aluminum from a stand.

-Take a horseshoe magnet and position it so that the magnetic field points upward. The north pole should be at the bottom and the south pole at the top for this. The aluminum rod should be positioned between the magnet's two poles.

• Now attach the aluminum rod to a battery and insert the key, allowing current to flow from B to A.

• The aluminum rod will travel to the left as you watch.

• Change the current direction from A to B now.

• The aluminum rod goes to the right in this example.

• The direction of current and the direction of the magnetic field are perpendicular in this experiment. The movement of the aluminum rod is perpendicular to the current and magnetic field directions.

Fleming’s Left-Hand Rule: When the thumb, index finger, and ring finger of the left hand are held in mutually perpendicular directions, the index finger represents the magnetic field, the ring finger represents the electric current, and the thumb represents the direction of deflection in the current carrying conductor. We can quickly determine the direction of deflection by applying this rule.

29. Draw a labelled circuit diagram of a simple electric motor and explain its working. In what way these simple electric motors are different from commercial motors?

Ans: A coil between the two poles of a permanent magnet is known as ABCD. The coil is positioned such that the current flow is perpendicular to the magnetic field's direction.

• The coil's arms are joined to a split ring, which is divided into two halves, P and Q. Arms AB and CD are attached to the half P and half Q, respectively.

• The split rings are connected to two static brushes, X and Y, from which they receive power. From the interior, the split rings are insulated. The split rings are being passed through by an axle.

• The coil is powered by an electric current supplied by a battery. Current flows from point A to point B, and from point C to point D.

Working of Electric Motor:

When current travels from A to B, the coil's arm AB moves down, following Fleming's Left-Hand Rule. When current goes from C to D, on the other hand, the arm CD moves higher. When the coil does a half-turn, P of the split ring hits brush Y, and Q of the split ring does the opposite. As a result, the current direction is reversed. As a result, the current is now flowing from D to C and from B to A. CD is pushed down and AB is pushed up as a result of this. As a result, the coil continues to revolve.

30. Explain the phenomenon of electromagnetic induction. Describe an experiment to show that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases.

Ans: Michael Faraday showed electromagnetic induction for the first time in 1831. Electric currents are induced in the conductor when a conductor and magnetic field are moving relative to each other. Electromagnetic induction is the term for this phenomenon.

• Take two coils with a lot of spins on them. Let's pretend that one coil has 100 turns and the other has 50.

• Put a non-conducting cylinder through the coils.

• Attach a galvanometer to the coil with 50 turns.

• Connect a 100-turn coil to a battery and insert the key.

Observation: 

• When the key is turned on, the galvanometer shows deflection.

• When the key is turned off, the galvanometer shows deflection, but in the other direction.

• This demonstrates that whenever the magnetic field strength changes, current is induced in the coil.

31. Describe the working of an AC generator with the help of a labeled circuit diagram. What changes must be made in the arrangement to convert it to a DC generator?

Ans: A rectangular coil is inserted between the two poles of a permanent magnet and is known as ABCD.

• The coil's arms AB are attached to a ring R1, and the coil's arm CD is attached to a ring R2.

• R1 and R2 are connected to an axle and are isolated from the inside.

• A brush B1 makes contact with R1, and another brush B2 makes contact with R2.

• To display the flow and direction of current in the circuit, B1 and B2 are connected to a galvanometer.

AC Generator Operation: -The AC generator operates according to Fleming's Right Hand Rule.

• Electric current is induced in a coil when it is spun inside a magnetic field.

• Assume that the coil in this diagram is spinning clockwise. This indicates that AB is ascending and CD is descending.

• As AB moves upward, current flows from A to B.

• A CD's current flows from C to D as it moves down.

• The relative locations of AB and CD alter after half a rotation. Now that the CD is rising, the current is shifting from D to C. AB is also flowing down, therefore the current is shifting from B to A.

• As a result, the direction of current in this generator switches every half round. This indicates that alternating current is being produced.

• Converting an AC generator to a DC generator entails the following steps. A split ring commutator is used for this.

32. Draw an appropriate schematic diagram showing common domestic circuits and discuss the importance of fuse. Why is it that a burnt-out fuse should be replaced by another fuse of identical rating?

Ans:

Important of Fuse:

In residential wiring and electrical equipment, fuses are an important safety device.

• A fuse protects the circuit and the device from harm caused by an overload.

• A fuse protects against an unintentional fire caused by a short circuit.

• A fuse with a certain rating is used with a specific appliance

• A fuse with a lower rating would be inconvenient to use since it would need to be changed often. Even if the current surpassed the device's maximum, a fuse with a higher rating would be useless since it would not melt. As a result, you should replace a blown fuse with one of the same rating.

Overview of NCERT Exemplar for Class 10 Science

This particular component helps students to score well in their board examinations. This material will give you answers to questions provided in the NCERT exemplar book. This NCERT exemplar book has extra questions to make the students completely prepared for the exam. 

Chapter 13 in the NCERT science book of Class 10 deals with the Magnetic effects of Electric Current, magnetic fields and electro-magnetic effects. Students will study various concepts related to electromagnets, electric motors, electric generators and the magnetic effect of electromagnets and electric generators as well. The chapter aims to make students understand electric currents and their magnetic effects

The exemplar has answers to various questions in multiple formats like MCQs, short answers and long answers to help students practice different formats. This will add up to your knowledge and help you clear various competitive exams. Students can download free PDF materials from the below-given links. For more materials and information, keep visiting Vedantu.