Magnetic Effects of Electric Current · Class 10 Science: 216 MCQs with answers

Q1. The direction of a magnetic field at a point is given by the direction of the:

Q2. What is a magnetic field? How is its direction at a point determined?

Q3. List four properties of magnetic field lines.

Q4. Why don't two magnetic field lines intersect each other?

Q5. Describe Oersted's experiment and its conclusion.

Q6. Where is the magnetic field of a bar magnet (a) strongest, (b) weakest? How does the field-line diagram show this?

Q7. Bring a bar magnet up to a compass and the needle swings. What accounts for that?

Q8. Describe the magnetic field produced by a straight current-carrying conductor, and state the rule for its direction.

Q9. State two factors on which the magnetic field due to a straight current-carrying wire at a point depends, and how.

Q10. What is a solenoid? Sketch-in-words its field pattern.

Q11. What is meant by a uniform magnetic field? Where do we obtain one?

Q12. What is an electromagnet? State the purpose of the soft iron core.

Q13. The rod experiment's force is largest when the horseshoe magnet's field and the rod are:

Q14. State Fleming's left-hand rule.

Q15. Under what conditions is the force on a current-carrying conductor in a magnetic field (a) maximum, (b) zero?

Q16. What will happen to the direction of the force if (a) only the current is reversed, (b) only the field is reversed, (c) both are reversed?

Q17. Name the rule you would use to determine (a) the field around a current-carrying wire, (b) the force on a current-carrying wire in a field — and state which hand each uses.

Q18. Iron filings around a magnet arrange in patterns because each filing:

Q19. Moving away from a bar magnet along its axis, the field lines are seen to spread further and further apart. This shows that the field is:

Q20. If a compass needle placed at a point does NOT deflect at all, the field there is:

Q21. A compass at a point P near a bar magnet points 30° east of north. The magnetic field at P points:

Q22. The density of field lines in a diagram represents the field's:

Q23. Which statement about magnetic poles is TRUE?

Q24. The needle of a compass is made of:

Q25. Earth's magnetic field would make a dip-free compass at the equator point:

Q26. Which everyday observation is direct evidence of Earth's magnetic field?

Q27. If Earth's magnetic field suddenly vanished, which device would fail first?

Q28. The field lines around a magnet spread out with distance because the field:

Q29. In the compass-tracing activity, each new compass position is placed:

Q30. Magnetic effect of current means:

Q31. Which needs BOTH magnitude and direction to be described fully?

Q32. Describe the activity of drawing field lines of a bar magnet using a small compass.

Q33. A magnet attracts an iron nail, and a magnet also attracts another magnet. Why is repulsion considered the surer test of magnetism?

Q34. State what happens, and why, when a bar magnet is broken into three pieces.

Q35. Draw (describe) the magnetic field pattern of a bar magnet and explain all the properties of magnetic field lines, justifying each.

Q36. Explain Oersted's experiment in detail — setup, observations, conclusion — and discuss why this discovery is considered the foundation of electromagnetism.

Q37. The magnetic field at a fixed point near a straight wire can be increased by:

Q38. A wire is wound into a long, closely-packed cylindrical coil of many turns. This arrangement is called a:

Q39. Which group lists ONLY changes that would strengthen an electromagnet?

Q40. The current through a solenoid is reversed. What happens to its magnetic field?

Q41. Doubling the number of turns in a coil (same current) makes the field at its centre:

Q42. A current flows vertically upward in a wire. Viewed from ABOVE, the field circles run:

Q43. The uniform field needed for many experiments is best produced:

Q44. Equally spaced, parallel field lines in a region represent:

Q45. An electric bell's hammer vibrates because the electromagnet:

Q46. Scrapyard cranes use electromagnets, not permanent magnets, because they need to:

Q47. A steel rod left inside a solenoid carrying current for some time becomes:

Q48. The strength of the field inside a solenoid does NOT depend on its:

Q49. An air-core solenoid's field is B. Inserting a soft-iron core makes the field:

Q50. The correct order of field strength (same current) at these points near a straight wire — P at 1 cm, Q at 2 cm, R at 4 cm — is:

Q51. Why does the magnetic field at the centre of a current loop appear as (nearly) straight lines?

Q52. How will the field of a solenoid change if (a) the current is increased, (b) the number of turns is increased, (c) a soft iron core is inserted?

Q53. Distinguish between an electromagnet and a permanent magnet. Give one use of each.

Q54. Why does a scrapyard crane use an electromagnet rather than a strong permanent magnet?

Q55. Describe the activity to demonstrate the magnetic field pattern of a straight current-carrying conductor using iron filings and a compass, state the observations, the rule for direction, and the two dependence relationships.

Q56. Which group correctly pairs each finger of Fleming's left-hand rule with what it represents?

Q57. Field into the page (×), current to the right. The force is directed:

Q58. Field out of the page (•), current to the right. The force is:

Q59. A wire lies exactly along the field lines of a magnet and carries a large current. The force on it is:

Q60. In a loudspeaker, the cone vibrates because the coil's force:

Q61. Which change does NOT alter the magnitude of the force on the rod?

Q62. The rod in the demo is displaced LEFT. To displace it RIGHT with the same magnet, one should:

Q63. In a galvanometer, the restoring turn against the coil's twist is provided by:

Q64. Which instrument is essentially a sensitive galvanometer with a scale calibrated in amperes?

Q65. The force on a conductor in a field acts:

Q66. The devices that do NOT depend on the force on a current in a field:

Q67. Why does a current-carrying conductor kept in a magnetic field experience a force?

Q68. Describe the aluminium-rod activity demonstrating the force on a conductor, with its observations.

Q69. How is the force on a current in a magnetic field used in an electric motor?

Q70. How does a loudspeaker produce sound using this force?

Q71. Which group correctly pairs each wire with its normal potential?

Q72. The correct order of connections from the supply is:

Q73. A switch placed in the neutral wire is dangerous because:

Q74. The earth pin is made LONGER than the other two so that:

Q75. Which appliance does NOT strictly need earthing?

Q76. Which of these events blows the fuse?

Q77. The main benefit of separate 5 A and 15 A circuits is:

Q78. In a fault, the earth wire carries current because it offers:

Q79. The insulation of old wiring cracks with age. The immediate risk is:

Q80. An MCB differs from a fuse in that it:

Q81. Why are the live and neutral wires of a cord kept insulated from each other?

Q82. Which practice is UNSAFE?

Q83. The energy meter is sealed by the electricity board because:

Q84. Consider these statements about a magnetic field. I. It is the region in which a magnet's force can be detected. II. It has both a magnitude and a direction at every point. III. Its direction at a point is where a compass needle's north pole points. IV. It exists only outside the magnet, not inside it. Which statements are correct?

Q85. A field line is traced with a plotting compass, starting at the north pole of a bar magnet. Following it all the way round, the line returns to its starting point after passing:

Q86. Why must magnetic field lines form closed loops, when electric field lines can simply begin and end on charges?

Q87. Iron filings sprinkled round a bar magnet settle into curved chains. They do this because each filing:

Q88. In a field-line diagram, how can you tell where the field is strongest without any numbers being given?

Q89. Two magnetic field lines can never cross, because at the crossing point:

Q90. A steel bar and a bar magnet both attract a piece of iron. Which single test would settle whether the steel bar is itself magnetised?

Q91. A bar magnet is cut in half, and each half is cut in half again. The result is:

Q92. A compass placed near a wire deflects the moment a current is switched on. The conclusion that follows is that:

Q93. A steel bar attracts one end of a suspended magnet. Why does this NOT prove the bar is itself a magnet?

Q94. A magnet suspended freely by a thread always settles roughly north-south. The reason is that:

Q95. A field line near a magnet is a curve, yet the field at any point has a single definite direction. The two are reconciled because the direction is given by:

Q96. In Oersted's experiment the current through the wire is reversed. The compass needle then:

Q97. Two bar magnets are placed with a north pole facing a south pole, a small gap between them. In that gap the field lines:

Q98. Between two facing LIKE (north) poles, at the exact midpoint the field is:

Q99. Assertion: Field lines are closed curves. Reason: Outside a magnet they run N→S and inside S→N, completing loops.

Q100. Assertion: Two field lines can never intersect. Reason: The field at a point can have only one direction.

Q101. A strong magnet and a weak magnet of the same size are mapped. The stronger magnet's diagram shows:

Q102. A compass moved slowly from near a magnet's N pole along a field line to its S pole will:

Q103. The deflection of Oersted's compass increases when:

Q104. The geographic north of Earth behaves magnetically like a:

Q105. A magnet attracts an unmagnetised iron nail because:

Q106. Case: A student draws field lines that cross near the pole 'because the field is strong there'. The examiner cuts marks because:

Q107. The unit 'oersted' is related to:

Q108. A plotting compass near a wire shows NO deflection even with a large current. The most likely reason is:

Q109. What can you say about the field if field lines drawn in a region are (a) parallel and equally spaced, (b) getting closer together along the direction of travel?

Q110. A student is given two identical-looking steel bars, only one of which is a magnet. Explain TWO different methods to identify the magnet, with the physics behind each.

Q111. With diagrams described in words, compare the field-line patterns of (a) a single bar magnet, (b) two unlike poles facing each other, and (c) two like poles facing each other — and state where each configuration's field is strongest or cancels.

Q112. Consider these statements about the field around a straight current-carrying wire. I. The field lines are concentric circles centred on the wire. II. They lie in a plane perpendicular to the wire. III. The field weakens with distance from the wire. IV. The field lines run parallel to the wire. Which statements are correct?

Q113. A student uses Fleming's left-hand rule to find the direction of the magnetic field produced BY a current. The mistake is that:

Q114. A vertical wire carries a current flowing UPWARDS. Seen from above, the magnetic field lines circle the wire:

Q115. In the iron-filings pattern round a straight current-carrying wire, the circles are crowded near the wire and spread out further away. This shows that:

Q116. Why is a solenoid, rather than a bar magnet, used to magnetise a steel rod?

Q117. The field lines inside a long current-carrying solenoid are drawn straight, parallel and equally spaced. Together these tell you that the field there is:

Q118. An electromagnet built with a STEEL core instead of soft iron would fail because the steel:

Q119. A scrapyard crane picks up iron, carries it across the yard and drops it. Which property of its electromagnet makes the DROP possible?

Q120. Why must the wire used to wind a solenoid be INSULATED?

Q121. A circular coil is viewed face-on and the current is seen to flow CLOCKWISE. The face towards the viewer behaves as:

Q122. Why is the field at the centre of a circular loop much stronger than the field near a straight wire carrying the same current?

Q123. A card is pierced by a vertical current-carrying wire and iron filings are sprinkled on it. Why must the card be TAPPED gently before the pattern appears?

Q124. A current flows vertically DOWNWARD in a straight wire. Viewed from ABOVE, the magnetic field circles run:

Q125. A compass placed directly EAST of a wire carrying current vertically upward will point (field circles anticlockwise from above):

Q126. Two parallel wires carry currents in the SAME direction. Their fields between the wires:

Q127. Assertion: A solenoid with current behaves like a bar magnet. Reason: Its field emerges from one end and enters the other, exactly like N and S poles.

Q128. Assertion: An electromagnet loses its magnetism when the circuit is switched off. Reason: Soft iron does not retain magnetism in the absence of a magnetising field.

Q129. A horizontal wire carries current from south to north. Directly ABOVE the wire, the field points (use the right-hand rule):

Q130. The field at the centre of a loop of radius r doubles if:

Q131. A solenoid hangs freely from a thread with current flowing. It will:

Q132. The plotting compass placed at the centre of a vertical current loop aligns:

Q133. Case: A relay uses a small 6 V circuit to switch a heavy 220 V machine. The 6 V current energises:

Q134. Case: A student's electromagnet lifts 20 pins. To lift more pins WITHOUT changing the battery, she should:

Q135. The field circles around a wire and the straight lines inside a solenoid are BOTH:

Q136. Which produces NO magnetic field?

Q137. Inside a solenoid connected to AC (rapidly alternating current), a soft iron core would:

Q138. A wire carries current vertically downward. What is the direction of its magnetic field at a point to its (a) east, (b) west? (Use the right-hand thumb rule.)

Q139. Explain the magnetic field of a current-carrying solenoid: its external pattern, its internal field, how to identify its poles, and why it can be used to magnetise a steel bar. Compare it point-by-point with a bar magnet.

Q140. With a labelled description, explain the construction and working of an electric bell, identifying every place where the magnetic effect of current is used.

Q141. Design an experiment to show that the magnetic field at the centre of a coil depends on (a) the current and (b) the number of turns. Describe the setup, procedure, expected observations and conclusions.

Q142. Consider these statements about a current-carrying conductor in a magnetic field. I. It experiences a force. II. The force is greatest when the current is perpendicular to the field. III. The force is zero when the current is parallel to the field. IV. The force acts along the direction of the current. Which statements are correct?

Q143. A student uses the right-hand thumb rule to find the direction of the force on a current-carrying rod placed between two magnet poles. The error is that:

Q144. A horizontal wire carries a current towards the NORTH in a magnetic field directed vertically DOWNWARDS. Using Fleming's left-hand rule, the force on it acts towards the:

Q145. A wire carries a current towards the EAST in a horizontal magnetic field pointing NORTH. The force on the wire is directed:

Q146. Why must the three fingers in Fleming's left-hand rule be held mutually perpendicular?

Q147. A rod carrying a current is rotated from being perpendicular to a magnetic field until it lies along the field. During this rotation the force on it:

Q148. A student passes a large current through a rod held between two magnet poles and it does not move at all. The most likely explanation is that:

Q149. In the rod-and-magnet demonstration, BOTH the current and the magnet's poles are reversed together. The rod then moves:

Q150. Why is the rod in the classic force demonstration made of aluminium rather than iron?

Q151. Two long parallel wires carry currents in the SAME direction. The force between them is:

Q152. A loudspeaker's cone moves back and forth in step with an audio signal. The reason the cone follows the signal faithfully is that:

Q153. In a moving-coil galvanometer, why is the pointer's deflection proportional to the current?

Q154. Which group lists ONLY changes that would increase the force on a current-carrying rod in a magnetic field?

Q155. A rod between magnet poles is pushed downwards when the current flows. Which single change would make it push UPWARDS instead?

Q156. A straight wire lies perpendicular to a magnetic field and experiences a force F. If the length of wire inside the field is doubled while the current and the field stay the same, the force becomes:

Q157. Field pointing north (horizontal), current flowing vertically upward. The force points:

Q158. A horizontal wire carries current east; the field points vertically down. The force on the wire points:

Q159. A wire carries a current vertically DOWNWARD in a horizontal magnetic field that points EAST. The force on the wire is directed:

Q160. An electron beam moves to the RIGHT through a field pointing INTO the page. The beam deflects (current is opposite to electron motion):

Q161. Assertion: A current-carrying conductor parallel to a magnetic field experiences no force. Reason: The force requires a component of current perpendicular to the field.

Q162. Assertion: Fleming's left-hand rule cannot be applied with the right hand. Reason: Using the right hand with the same finger assignments gives the OPPOSITE force direction.

Q163. The kicking-rod experiment shows the force is perpendicular to:

Q164. Assertion (A): The force on a current-carrying conductor is always perpendicular to the plane containing the current and the magnetic field. Reason (R): Fleming's left-hand rule requires the thumb, forefinger and middle finger to be held mutually perpendicular.

Q165. Two parallel wires carry currents in opposite directions. The force between them is:

Q166. Case: A wire carrying 5 A perpendicular to a field feels force F. At 2.5 A in the same setup, the force is:

Q167. Case: In a school demo the rod barely moves. Which fix will NOT help?

Q168. A straight wire in a magnetic field is turned from parallel to perpendicular. What happens to the magnetic force, assuming current and field strengths stay fixed?

Q169. A charged particle at REST in a magnetic field experiences:

Q170. A horizontal power cable carries current from west to east. Earth's magnetic field at that place points from south to north (horizontal). Find the direction of the force on the cable.

Q171. An electron beam enters a magnetic field directed into the page, moving from left to right. In which direction does the beam deflect?

Q172. Describe, with full experimental detail, the activity showing that a current-carrying conductor experiences a force in a magnetic field. Include the setup, four observations with their conclusions, and the rule that summarises the directions.

Q173. State Fleming's left-hand rule and apply it to find the force direction in each case: (a) current east, field vertically downward; (b) current vertically up, field north; (c) current north, field north; (d) electron beam moving south in a field vertically downward.

Q174. Explain how the force on a current-carrying conductor in a magnetic field is put to work in (a) the electric motor's principle, (b) the loudspeaker, and (c) the moving-coil galvanometer — identifying in each device what provides the field, what carries the current, and what the force achieves.

Q175. A straight conductor of length l carrying current I lies in a uniform magnetic field B. Discuss qualitatively how the force on it changes as: (a) I is doubled, (b) B is halved, (c) l in the field is doubled, (d) the conductor is rotated from perpendicular to parallel with the field — and combine (a)–(c) into a single proportionality statement.

Q176. Consider these statements about domestic wiring in India. I. The live wire is red and at about 220 V. II. The neutral wire is black and at about 0 V. III. The earth wire is green and normally carries no current. IV. Switches are placed in the neutral wire. Which statements are correct?

Q177. A person touches the neutral wire of a working circuit and feels almost nothing, while touching the live wire would be dangerous. The reason is that:

Q178. The Indian mains supply is 220 V AC at 50 Hz. The figure 50 Hz means that the current:

Q179. Why must domestic appliances be connected in parallel rather than in series?

Q180. Why is a fuse placed in the live wire rather than the neutral wire?

Q181. Why does a house have a separate 15 A circuit in addition to the 5 A lighting circuit?

Q182. Why are bulbs and fans wired on the 5 A circuit rather than the 15 A one?

Q183. The live wire inside an earthed metal-bodied appliance comes loose and touches the casing. What happens?

Q184. Why does a plastic-bodied table lamp not need an earth connection, while a metal-bodied refrigerator does?

Q185. What makes a short circuit so dangerous so quickly?

Q186. A family plugs a heater, an iron and a geyser into one multi-plug adaptor and the fuse blows. The fault is:

Q187. Which group correctly distinguishes the two faults a fuse guards against?

Q188. Someone breaks the third pin off a geyser's plug to fit it into a two-pin socket. The consequence is that:

Q189. A household electricity meter records the number of units consumed. One unit corresponds to:

Q190. An ELCB/RCCB trips when it detects:

Q191. A bird sits safely on one live high-voltage wire because:

Q192. During a shower, a person touches a FAULTY unearthed geyser. Current flows through them because:

Q193. Assertion: Earthing plus a fuse together protect a user from a leaking appliance. Reason: The earth wire carries the fault current to the ground, and this large current melts the fuse, cutting supply.

Q194. Assertion: A short circuit can start a fire. Reason: The near-zero resistance lets a huge current flow, producing intense I²R heating in the wires.

Q195. A 15 A circuit at 220 V can safely carry appliances totalling at most about:

Q196. A 5 A lighting circuit already carries ten 40 W bulbs (400 W ≈ 1.8 A). Adding a 2000 W heater (≈9 A) to it causes:

Q197. The maximum number of 100 W bulbs a 5 A, 220 V circuit can safely run is:

Q198. Case: Every evening when the geyser, iron and microwave run together, the kitchen MCB trips. The problem is:

Q199. Case: The MCB trips the INSTANT a frayed table-lamp cord is plugged in, every time. The problem is:

Q200. In modern colour code (international), the live wire is: