SolveIt is under development
SolveItNCERT · CBSE · NEET

NCERT Exemplar · Class 10 Science Magnetic Effects of Electric Current

32 questions · 32 still being checked

Long Answer Questions 25–32 (part 3 of 3)

  1. Exercise 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.

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    Current carrying loops behave like bar magnets and both have their associated lines of field. This modifies the already existing earth's magnetic field and a deflection results. Magnetic field has both direction and magnitude. Magnetic field lines emerge from N-pole and enter S-pole. The magnetic field strength is represented diagrammatically by the degree of closeness of the field lines. Field lines cannot cross each other as two values of net field at a single point cannot exist. Only one value, a unique net value, can exist. If in a given region, lines of field are shown to be parallel and equispaced, the field is understood to be uniform.
    Free of a nearby magnet, the needle simply settles along \(\displaystyle \vec B_{Earth}\). A bar magnet or current loop nearby adds its own field at the needle's site: \[\vec B_{net} = \vec B_{Earth} + \vec B_{magnet} \] so the needle's torque aligns it with \(\displaystyle \vec B_{net}\) instead — it deflects. Field lines: leave N, enter S outside the magnet, continue S to N inside (closed curves); tangent gives the field direction; closer lines mean a stronger field; no two lines ever cross. Answer: The needle follows the resultant \(\displaystyle \vec B_{net}\), not Earth's field alone. Field lines run N to S outside (closed loops, S to N inside), tangent gives direction, spacing shows strength, and they never cross.

  2. Exercise 26

    With the help of a labelled circuit diagram illustrate 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 direction of magnetic field associated with a current carrying conductor?

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    Right hand thumb rule states that if a current carrying straight conductor is supposedly held in the right hand with the thumb pointing towards the direction of current, then the fingers will wrap around the conductor in the direction of the field lines of the magnetic field. NCERT_Solution_Class10_Science_Exemplar_Ch13_Q26_ncert
    Circuit: cell, key and rheostat in series with a long straight wire through a horizontal cardboard sheet; sprinkle iron filings over the sheet and close the key. Tap the sheet gently — the filings align into concentric circles centred on the wire (without a tap they stay clumped, no pattern shows). Right-hand thumb rule: grip the wire with the thumb along the current; the curled fingers then give the field lines' direction. Answer: Field lines are concentric circles centred on the wire. Right-hand thumb rule: thumb along the current, curled fingers show the circles' direction.

  3. Exercise 27

    Explain with the help of a labelled 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\displaystyle n turns the field produced at any point is n\displaystyle n times as large as that produced by a single turn?

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    Hint— The magnetic field at a point is the addition of the field produced by each turn. NCERT_Solution_Class10_Science_Exemplar_Ch13_Q27_ncert
    Close to the wire the field lines are concentric circles; farther from it the circles grow larger, so at the centre of the loop their arcs look like straight lines, perpendicular to the plane of the loop.Each turn of a closely wound \(\displaystyle n\)-turn coil carries the same current in the same sense, so at any point each turn gives the same field \(\displaystyle B_1\), in the same direction (right-hand rule); the fields superpose: \[B_n = \underbrace{B_1 + B_1 + \cdots + B_1}_{n\ \text{turns}} = nB_1 \] Answer: lines circle the wire and are straight, perpendicular to the loop, at its centre; \(\displaystyle n\) turns give \(\displaystyle B_n = nB_1\).

  4. Exercise 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?

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    Hint— Explain the activity with the help of the diagram. According to Fleming's left hand rule, stretch the thumb, forefinger and central finger of your left hand such that they are mutually perpendicular. If the fore finger points in the direction of magnetic field and the central in the direction of current, then the thumb will point in the direction of motion or force acting on the conductor. NCERT_Solution_Class10_Science_Exemplar_Ch13_Q28_ncert
    Activity: suspend a rod AB between the poles of a horseshoe magnet, field N to S across it, rod perpendicular to that field; wire AB in series with a battery, key and rheostat. Closing the key sends current along AB and the rod jumps — up or down, by current's direction — a force perpendicular to both current and field; turned parallel to the field, the rod feels no force at all. Fleming's left-hand rule: forefinger along field, middle finger along current, thumb gives the force's (motion's) direction. Answer: The rod jumps perpendicular to both current and field (zero force if parallel to the field); Fleming's left-hand rule — forefinger = field, middle finger = current, thumb = force.

  5. Exercise 29

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

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    Hint— Explain working with the help of the diagram. Commercial motors use an electromagnet in place of a permanent magnet, a large number of turns of conducting wire in the current carrying coil and a soft iron core on which the coil is wound. NCERT_Solution_Class10_Science_Exemplar_Ch13_Q29_ncert
    Parts: coil ABCD between the poles N, S of a permanent magnet; its ends join the halves P, Q of a split-ring commutator; brushes X, Y touch the halves and connect to a battery. Current enters at X and runs \(\displaystyle A\to B\to C\to D\). Fleming's left-hand rule, field N \(\displaystyle \to\) S: \[AB:\ I\ (A\to B)\Rightarrow \vec F\downarrow \qquad CD:\ I\ (C\to D)\Rightarrow \vec F\uparrow \] The coil turns anticlockwise. The ring's gap must meet the brushes as the coil passes the vertical: the halves then swap brushes, the current reverses, and the push never opposes the turn. A commercial motor uses an electromagnet, many turns and a soft-iron core. Answer: The split ring reverses the coil current every half-turn, so rotation stays one way; a commercial motor adds an electromagnet, many turns, a soft-iron core.

  6. Exercise 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.

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    Hint— The process by which a changing magnetic field in a conductor induces a current in another conductor is called electromagnetic induction. Explain the working of the set up with the help of the diagram. NCERT_Solution_Class10_Science_Exemplar_Ch13_Q30_ncert
    Electromagnetic induction: a changing magnetic field linked with a closed loop drives a current in it, without any battery — the changing flux itself supplies the emf. \[\varepsilon = -N\dfrac{d\Phi_B}{dt} \] Experiment: connect a coil to a galvanometer, and plunge a bar magnet's N pole into the coil. The needle deflects one way as the magnet moves in and the other way as it is pulled out; holding it still inside gives no deflection — it is the change of flux, not its presence, that induces the current. Answer: A changing flux through a closed loop induces a current; a magnet moved in and out of a coil-galvanometer loop gives opposite deflections, and none when held still.

  7. Exercise 31

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

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    Explain working with the help of the diagram. To get a direct current a split ring type commutator must be used in place of slip ring type commutator. NCERT_Solution_Class10_Science_Exemplar_Ch13_Q31_ncert
    Parts: armature coil ABCD rotating between magnet poles, ends joined to two slip rings; fixed brushes ride the rings, wired to the external circuit. Turning the coil sweeps AB, CD through the field; by Fleming's right-hand rule an emf is induced, current leaving one brush, returning by the other. Each half-turn the sides swap poles, reversing the current — alternating current. Swap the slip rings for one split-ring commutator: it flips the connection every half-turn with the coil, so current always leaves one brush the same way — a DC generator. Answer: The rotating coil induces an alternating emf via slip rings and brushes, reversing each half-turn; a commutator instead flips the connection with the coil, giving one-way (DC) output.

  8. Exercise 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?

    Matches the book, not yet reviewed

    This working reaches the answer NCERT prints. It has not yet been read through by hand.

    NCERT’s answer
    Hint— A fuse in a circuit prevents damage to the appliances and the circuit due to overloading. Otherwise the appliances or the circuit may get damaged. NCERT_Solution_Class10_Science_Exemplar_Ch13_Q32_ncert
    Live and neutral wires enter through the supply fuse, then the meter, then the main switch in the distribution box, and split into lighting and power circuits, each with its own fuse; the earth wire joins each appliance's metal body to ground. A fuse is a thin, low-melting-point wire in series with the live wire: \[H = I^2 R t \] \[\text{short circuit or overload} \Rightarrow I\uparrow \Rightarrow H\uparrow \Rightarrow \text{fuse melts} \Rightarrow \text{circuit opens} \] The break comes before the wiring and appliances overheat. Replace it only with the same rating: \[\text{rating too high} \Rightarrow \text{wiring overheats before the fuse melts} \] \[\text{rating too low} \Rightarrow \text{fuse melts on normal load current} \] Answer: A fuse melts and breaks the circuit on a fault current, before the wiring and appliances overheat; an identical rating is needed because a higher one stops protecting and a lower one blows on normal load.