Question Bank — Magnetic Effects of Electric Current

NCERT Class 10 Science · Chapter 12 · CBSE Board Pattern

Class 10 Science Chapter 12 Question Bank CBSE Board Pattern

Section A — MCQs (1 mark each)

  1. The magnetic field lines around a straight current-carrying conductor form
    (a) straight lines parallel to the wire
    (b) concentric circles centred on the wire
    (c) radial lines originating from the wire
    (d) straight lines perpendicular to the wire

  2. Inside a long current-carrying solenoid the magnetic field is
    (a) zero
    (b) maximum at the ends and zero at the centre
    (c) uniform and parallel to the axis
    (d) stronger near the turns and weaker at the centre

  3. Assertion (A): Magnetic field lines never intersect each other.
    Reason (R): If two field lines intersected, a compass needle placed at the intersection would point in two different directions at the same time.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

  4. Assertion (A): The strength of the magnetic field due to a current-carrying straight wire increases with increase in current.
    Reason (R): The magnetic field at a point due to a straight conductor is directly proportional to the current passing through it.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

  5. Fleming’s left-hand rule is used to find the direction of
    (a) magnetic field around a straight conductor
    (b) force on a current-carrying conductor placed in a magnetic field
    (c) induced current in a coil
    (d) magnetic field inside a solenoid

  6. When the direction of current through a straight conductor is reversed, the direction of the magnetic field lines around it
    (a) remains the same
    (b) reverses
    (c) becomes radial
    (d) disappears

  7. The earth wire in a domestic circuit is usually covered with
    (a) red insulation
    (b) black insulation
    (c) green insulation
    (d) no insulation

  8. A current-carrying circular loop produces a magnetic field that at its centre appears as
    (a) concentric circles
    (b) straight lines
    (c) elliptical loops
    (d) radial lines

  9. Overloading in a domestic circuit can occur when
    (a) too many appliances are connected to one socket
    (b) the live and neutral wires come into direct contact
    (c) the fuse wire melts
    (d) both (a) and (b)

  10. The magnetic field produced by a current-carrying solenoid can be used to
    (a) heat a conductor
    (b) magnetise a soft-iron core placed inside it
    (c) increase the resistance of the circuit
    (d) produce electric sparks

Section B — Very Short Answer (2 marks each)

  1. State the right-hand thumb rule and give one situation where it is applied.
  2. Why does the deflection in a compass needle placed near a current-carrying straight wire increase when the current is increased?
  3. List two properties of magnetic field lines.
  4. What is the function of the earth wire in a domestic electric circuit?
  5. How does the magnetic field due to a current-carrying circular loop change as we move away from the loop along its axis?
  6. Differentiate between a solenoid and a bar magnet on the basis of the nature of the magnetic field inside them.

Section C — Short Answer (3 marks each)

  1. Draw the pattern of magnetic field lines around a current-carrying straight conductor. Mark the direction of current and the direction of the magnetic field at any one point.
  2. With the help of a labelled diagram, explain how an electromagnet is made using a solenoid. State one advantage of an electromagnet over a permanent magnet.
  3. A current-carrying conductor is placed perpendicular to a magnetic field. State Fleming’s left-hand rule and use it to predict the direction of force when both current and field directions are reversed simultaneously.
  4. Why is a fuse wire always connected in series with the live wire in a domestic circuit? What happens during short-circuiting?
  5. Explain, with reason, why the magnetic field inside a current-carrying solenoid is uniform while outside it the field resembles that of a bar magnet.

Section D — Long Answer (5 marks each)

  1. (a) Draw a neat labelled diagram showing the magnetic field lines around a current-carrying solenoid. Mark the north and south poles.
    (b) State two ways in which the strength of this magnetic field can be increased.
    (c) How is the field inside the solenoid different from the field outside it?

  2. Describe an activity to show that a current-carrying conductor experiences a force when placed in a magnetic field. Draw the labelled diagram of the arrangement used. State the rule that gives the direction of this force and mention two devices that work on this principle.

  3. (a) Draw the schematic diagram of a typical domestic electric circuit showing the live, neutral and earth wires, the main fuse, switches and a few appliances connected in parallel.
    (b) Explain, with reasons, any two safety measures used in this circuit to prevent damage due to overloading or short-circuiting.

Section E — Case/Source-Based (4 marks each)

Case 1

In a school laboratory, students pass current through a long straight thick copper wire fixed vertically through a cardboard. Iron filings are sprinkled on the cardboard and the key is closed. Concentric circles of iron filings are seen around the wire. When a compass is placed at different points on one circle, its north pole points in the direction of the circle. On increasing the current, the circles become more distinct and the compass deflection increases. On reversing the current, the compass needle reverses its direction.

Sub-questions:
(i) What do the concentric circles represent? (1)
(ii) Name the rule used to find the direction of the magnetic field and state it briefly. (1)
(iii) Why does the deflection of the compass needle increase when current is increased? (1)
(iv) What will happen to the pattern if the cardboard is moved farther away from the middle of the wire while keeping current constant? Give reason. (1)

Case 2

A rectangular coil of insulated copper wire having many turns is connected to a battery through a rheostat and a key. The coil is placed between the pole pieces of a strong horse-shoe magnet so that the plane of the coil is perpendicular to the magnetic field. When current is passed, the coil experiences a force and tends to move. On reversing the current, the direction of force reverses. The force is maximum when the current and field are at right angles.

Sub-questions:
(i) Name the rule that gives the direction of force on the coil. (1)
(ii) If the number of turns in the coil is doubled while keeping current and field the same, what happens to the force experienced by the coil? Why? (1)
(iii) Name two devices that work on the same principle. (1)
(iv) What change in the arrangement would make the force zero? (1)

Section F — HOTS and Application (3 marks each)

  1. Predict-and-justify: What would happen to the magnetic field lines inside a solenoid if the soft-iron core is removed while the current remains constant? Justify your answer.
  2. Analyse an anomalous observation: In an experiment, a compass needle placed exactly at the centre of a current-carrying circular loop shows almost no deflection, while the same compass shows large deflection when placed near the wire. Explain this observation.
  3. Unfamiliar real-life situation: A technician observes that the metal body of a newly installed geyser gives a mild shock when touched, although the live and neutral connections are correct. Which safety device is probably missing or not connected properly? Explain how its proper connection would have prevented the shock.
  4. Compare two situations: Two identical straight conductors carry the same current. In case I the conductor is straight; in case II the same length of conductor is bent into a single circular loop. In which case is the magnetic field at the centre stronger? Justify using the chapter concepts.
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( marking points given in CBSE style; full working shown where applicable)

Section A

  1. (b)
  2. (c)
  3. (a)
  4. (a)
  5. (b)
  6. (b)
  7. (c)
  8. (b)
  9. (d)
  10. (b)

Section B

  1. Right-hand thumb rule: Hold conductor in right hand with thumb pointing in direction of current; curled fingers give direction of magnetic field. Applied for straight conductor. (definition 1, application 1)
  2. Magnetic field ∝ current; larger current → stronger field → larger deflection. (1+1)
  3. Any two: closed curves, emerge from N and enter S, closer lines = stronger field, never intersect. (1+1)
  4. Provides low-resistance path for leakage current to earth, prevents electric shock. (1+1)
  5. Field decreases with distance; at large distance arcs appear almost straight. (1+1)
  6. Inside solenoid: uniform parallel lines; inside bar magnet: from S to N. (1+1)

Section C

  1. Concentric circles, current arrow, field direction marked at one point. (diagram 2, labelling 1)
  2. Diagram of solenoid with soft-iron core, battery, north-south poles marked; advantage: strength can be changed by changing current. (diagram 2, explanation 1)
  3. Fleming’s left-hand rule stated; force direction reverses when both are reversed (net direction same). (rule 1, reasoning 2)
  4. Fuse melts on overload/short-circuit, breaks circuit; placed in live wire so appliance is isolated. (2+1)
  5. Inside: field lines parallel and equally spaced; outside: spread out like bar magnet. (2+1)

Section D

  1. (a) Labelled solenoid diagram with field lines inside parallel and outside like bar magnet, N-S poles marked (3 marks). (b) Increase current or number of turns (1). (c) Uniform inside, non-uniform outside (1).
  2. Activity 12.7 description with labelled diagram (rod AB, magnet, battery); Fleming’s left-hand rule; electric motor, loudspeaker (diagram 2, activity 2, rule+devices 1).
  3. (a) Labelled domestic circuit diagram (live red, neutral black, earth green, main fuse, parallel appliances) (3). (b) Any two safety points: fuse, earthing, separate circuits for high/low power (2).

Section E

Case 1: (i) Magnetic field lines (1) (ii) Right-hand thumb rule (1) (iii) B ∝ I (1) (iv) Circles become larger/weaker because field decreases with distance (1).
Case 2: (i) Fleming’s left-hand rule (1) (ii) Force doubles because each turn contributes additively (1) (iii) Electric motor, loudspeaker (1) (iv) Current parallel to field or current zero (1).

Section F

  1. Field inside becomes non-uniform and weaker (no soft-iron core to concentrate lines); lines spread out. (prediction 1, justification 2)
  2. At exact centre of loop, field due to every element adds in same direction but resultant may appear weak if loop radius large; near wire field is strong due to proximity. (observation analysis 3)
  3. Earth wire missing/not connected; it would conduct leakage current safely to earth keeping body at zero potential. (identification 1, explanation 2)
  4. Case II (loop) has stronger field at centre because fields due to all parts add constructively at centre; straight wire field at any external point is weaker. (comparison 1, reason 2)
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All questions are answerable from the NCERT chapter text. Reviewed by GFIS faculty.