🧲 UNIT – 12 : MAGNETIC EFFECTS OF ELECTRIC CURRENT(Question )

 

🧲 UNIT – 12 : MAGNETIC EFFECTS OF ELECTRIC CURRENT

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I. Multiple Choice Questions (1 Mark each)

1. The magnetic poles represented by P and Q are
    A) South (S) and South (S) B) North (N) and South (S) C) North (N) and North (N) D) South (S) and North (N)

2. Inside a solenoid, the magnetic lines of force are parallel straight lines. Therefore, the magnetic field inside the solenoid is
    A) Very high B) Uniform C) Zero D) Caused by electric current

3. Which of these is not a characteristic of magnetic lines of force?
    A) Dense near poles B) Closed loops C) Intersect each other D) Emerge from North, enter South

4. When you hold a straight conductor carrying current with your right thumb pointing upwards, the magnetic field lines are
    A) Downward B) Upward C) Anticlockwise D) Clockwise

5. The magnetic field inside a long solenoid carrying current is
    A) Same at all points B) Zero C) Decreases at ends D) Increases at ends

6. In Fleming’s left-hand rule, the middle finger shows the direction of
    A) Magnetic field B) Electric current C) Motion of conductor D) Induced current

7. A rod carrying current is placed between the poles of a magnet. The angle for maximum displacement is
    A) 0° B) 45° C) 90° D) 180°

8. If the number of turns in a circular conductor is increased 10 times, the magnetic field increases
    A) 100 times B) 10 times C) 20 times D) 1000 times

9. When a magnetic needle is brought near a current-carrying wire, the direction of deflection depends on
    A) Length of conductor B) Amount of current C) Direction of current D) Strength of needle

10. If magnetic lines of force are dense, magnetic field strength is
     A) High B) Low C) Neutral D) None

11. In Fleming’s left-hand rule, index finger indicates
     A) Magnetic field B) Current C) Motion D) Force

12. The safety method used to prevent damage by overload is
     A) Earthing B) Transformer C) Use of fuses D) Electricity meter

13. The appliance not suitable in 5A circuit is
     A) Bulb B) Mixer C) Fan D) Geyser

14. In case of short circuit, current
     A) Becomes very high B) Becomes low C) Neutral D) Changes continuously

15. The magnetic force is maximum in a bar magnet
     A) At N end B) At S end C) Between poles D) At both ends

16. The magnetic field around a long straight wire
     A) Consists of concentric circles B) Parallel lines C) Perpendicular lines D) Radiating rays

17. A student concludes from a diagram that
     A) Lines emerge from N, merge at S
     B) Field stronger where lines are denser
     C) No lines intersect
     D) All of the above

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II. One Mark Questions

18. Why do magnetic lines of force not intersect each other?

19. State any two measures to avoid overload in a domestic electrical circuit.

20. What is the cause of overload in a circuit?

21. What does the thumb indicate in the right-hand thumb rule?

22. Write two characteristics of magnetic lines of force around a solenoid.

23. Observe the circuit diagram — state the direction of magnetic field around point P and Q.

24. What is a magnetic field?

25. What are magnetic lines of force?

26. When does a current-carrying conductor experience the greatest force in a magnetic field?

27. Name some instruments that use current-carrying conductors in a magnetic field.

28. Why does a compass needle move when brought near a bar magnet?

29. Draw magnetic lines of force around a bar magnet.

30. List two methods of producing a magnetic field.

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III. Two Mark Questions

31. What are the causes of overload and short circuit in an electric circuit?

32. State two properties of magnetic lines of force.

33. What are the reasons for overload in a domestic circuit?

34. Why are electrical appliances with metal surfaces connected to the earth wire?

35. Observe the figure — state the direction of force acting on wire AB. Name the law used.

36. What is a solenoid? How can it be converted into an electromagnet?

37. Observe the given picture:
     i) Mention the direction of current.
     ii) State the rule used to determine this direction.

38. State two methods of increasing magnetic field in a solenoid.

39. Draw a diagram showing magnetic lines of force around a straight conductor. Identify:
     A) Direction of magnetic field B) Direction of current

40. Write the characteristics of the magnetic field inside a solenoid.

41. A microwave oven of 2 kW and 5A rating is used in a 220 V circuit. What effect would occur?

42. Write the rules used to determine direction of
     A) Magnetic field around straight conductor
     B) Force on conductor in magnetic field

43. In the given figure, identify whether P and Q are north or south poles. Justify.

44. A student says magnetic field at point A is greater than at B. Is this correct? Justify.

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IV. Three Mark Questions

45. How do you identify magnetic field lines around a bar magnet using a compass? Explain.

46. a) Which factor helps determine relative strength of a magnetic field?
     b) State the right-hand thumb rule and any two characteristics of magnetic force lines.

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V. Four Mark Questions

47. Explain the function of the earth wire in household electrical circuits.

48. Explain an experiment to show that a conductor carrying current experiences a force in a magnetic field.

🧲 UNIT — 12 : MAGNETIC EFFECTS OF ELECTRIC CURRENT — KEY ANSWERS

I. Multiple Choice Questions (1 mark each)

Q.No	Answer	Brief reason (as in model key)
1	A. South (S) and South (S)	Poles shown in figure are both S (as per given figure)
2	B. Uniform	Inside a long solenoid field lines are parallel ⇒ field uniform
3	C. Magnetic lines of force intersect each other	This is NOT a characteristic (they never intersect)
4	D. Clockwise	Right-hand rule gives direction of field (for thumb up)
5	A. Same at all points	Inside long solenoid field is same (uniform)
6	B. Electric current	(context: what produces the field — current)
7	C. 90°	Maximum force when conductor is perpendicular (90°) to field
8	B. 10 times	Field ∝ number of turns — 10× turns ⇒ ~10× field
9	C. Direction of electric current in a conductor	Needle deflection depends on current direction
10	A. High	High density of lines ⇒ strong field
11	A. Index finger	(Fleming’s left hand rule: index = field)
12	C. Use of fuses	Safety method to prevent overload damage
13	D. Geyser	Geyser draws large current — not suitable for 5 A circuit
14	D. Very high	In short circuit current becomes very large
15	D. At both ends	Magnetic effect strong at both pole ends
16	D. The wire is the center of the concentric magnetic lines	Field around straight wire = concentric circles

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II. One-mark answers (short)

18. Why lines don't intersect: If they did, field would have two directions at same point — impossible.

19. Measures to avoid overload: (any two) — do not connect many appliances to one socket; use good quality wires/appliances; avoid simultaneous heavy loads.

20. Cause of overload: Sudden increase in supply voltage / too many appliances on same socket / live and neutral shorting.

21. Right-hand thumb rule — thumb indicates: Direction of current; curled fingers show magnetic field.

22. Magnetic lines around solenoid — characteristics: At ends: concentric circles; inside: parallel straight lines (uniform field).

23. Direction at P & Q (given circuit): At P — anticlockwise; at Q — clockwise.

24. Magnetic field: Region around magnet/current where magnetic forces act.

25. Magnetic lines of force: Imaginary lines showing direction & strength of magnetic field.

26. Greatest force on conductor: When conductor direction is perpendicular to magnetic field.

27. Instruments using current + magnetic field: Electric motors, generators, loudspeakers, microphones, electrical meters.

28. Compass needle moves near bar magnet because: Interaction between magnet’s field and compass (small magnet) causes deflection.

29. Draw: Magnetic field lines emerge from N, enter S (draw smooth closed curves).

30. Two methods to produce magnetic field: (i) Permanent magnet, (ii) Electromagnet (current in coil/solenoid).

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III. Two-mark answers (concise model answers)

31. Causes of overload / short circuit: Faulty/damaged insulation; live and neutral touching; sudden voltage surge; too many appliances on one socket.

32. Two properties of magnetic lines: (i) No two lines intersect; (ii) Denser near poles → stronger field; lines form closed loops from N → S outside magnet.

33. Reasons for overload: Connecting many appliances to same socket; damaged insulation causing partial short; sudden supply voltage rise.

34. Why earth wire for appliances with metal body: Provides low-resistance path to earth so leakage current flows to ground → prevents electric shock.

35. Direction of force on AB (figure): (Answer depends on figure) — direction given by Fleming’s left-hand rule; state the direction shown and cite Fleming’s left-hand rule.

36. Solenoid & electromagnet: Solenoid = coil of many turns; insert soft iron core and pass current → becomes strong electromagnet.

37. Given picture — i) current direction: (state direction as in figure) ii) rule: Right-hand thumb rule (or Maxwell’s / Fleming’s as appropriate).

38. Ways to increase solenoid field: Increase number of turns; increase current; insert soft iron core.

39. Draw field around straight conductor: Concentric circles around wire; label (A) magnetic field direction (use right-hand rule), (B) direction of current.

40. Characteristics of field inside solenoid: Lines parallel, equally spaced ⇒ uniform; strong and similar to bar magnet (poles at ends).

41. 2 kW, 5 A microwave on 220 V circuit effect: P = 2000 W ⇒ I = P/V = 9.09 A — exceeds 5 A circuit rating ⇒ overload, heating, possible fuse blow / hazard.

42. Rules to determine directions: (A) Right-hand thumb rule for field around straight current; (B) Fleming’s left-hand rule for force on current-carrying conductor in magnetic field.

43. Poles P and Q (figure): P and Q are north poles (justify from repulsion of like poles / direction of field lines as in figure).

44. Is field at A > B? Yes — field stronger where lines are denser; justify by line density.

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IV. Three-mark answers (model / exam style)

45. Identify field lines with compass (method): Place compass near magnet; mark needle orientation at several positions around magnet (keeping south of compass to north of magnet etc.); join marked tips to draw smooth lines; repeat to get multiple lines showing field pattern. (Steps as in model key.)

46. (a) Factor determining field strength: density of field lines / current magnitude / number of turns in coil.
    (b) Right-hand thumb rule: Hold conductor in right hand with thumb along current — curled fingers show field direction. Two characteristics: lines are closed loops; denser near poles (stronger field); they do not intersect.

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V. Four-mark answers (model / exam style)

47. Function of earth wire: Earth/ground wire connects metal body of appliance to earth potential. If live wire leaks to metal case, earth wire provides low-resistance path and prevents the user receiving a shock; it causes fuse/MCB to trip and isolates the fault — safety measure.

48. Experiment showing force on current-carrying conductor: Place a straight conductor between poles of a strong magnet, pass current; observe conductor deflects; reverse current → deflection reverses. Use Fleming’s left-hand rule to determine direction; explain that maximum force when conductor is perpendicular to field and that force ∝ I × B × length (qualitative explanation as in model answer).