Magnetic Effects of Electric Current – MCQs with Answers and Explanations
CBSE • NCERT • Class 10
Physics — Chapter 12: Magnetic Effects of Electric Current — 60 MCQs
Topic-wise multiple choice questions with answers and clear explanations — ideal for NCERT-based CBSE Class 10 board exam practice.
Topics covered:
Magnetism basics, Oersted, right-hand rules, straight wire, circular loop, solenoid, electromagnets, force & motor, Fleming rules, induction & applications.
Magnetism basics, Oersted, right-hand rules, straight wire, circular loop, solenoid, electromagnets, force & motor, Fleming rules, induction & applications.
- Basic magnetism & field lines (Q1–6)
- Oersted & right-hand rules (Q7–12)
- Field of straight wire & loop (Q13–22)
- Solenoid & electromagnets (Q23–32)
- Force on conductor & motors (Q33–44)
- Fleming rules & applications (Q45–52)
- Electromagnetic induction & Lenz (Q53–60)
Q1 (Basics)
What is indicated by the spacing between magnetic field lines?
Answer: B
Closer field lines indicate stronger magnetic field; spacing shows relative magnitude, not current direction or temperature.
Q2 (Basics)
Field lines outside a bar magnet emerge from which pole?
Answer: C
By convention, external field lines go from north to south; inside magnet they return from south to north.
Q3 (Basics)
Which of these statements is true about magnetic field lines?
Answer: C
Field lines form continuous closed curves; they do not cross. They are a representation and can be visualised using iron filings.
Q4 (Basics)
A compass needle aligns tangentially to magnetic field lines because:
Answer: B
The magnetic moment of the needle experiences torque aligning it with the local magnetic field direction; it does not always point geographic north in presence of other fields.
Q5 (Basics)
Iron filings sprinkled around a magnet form patterns due to:
Answer: A
Iron filings align along local magnetic field directions showing field line patterns; not chemical or gravitational effect.
Q6 (Basics)
The magnetic field at a point is strongest where:
Answer: B
Density of lines indicates strength — dense region = strong field.
Q7 (Oersted)
Who discovered magnetic effect of electric current?
Answer: B
Oersted observed compass deflection near a current-carrying wire, demonstrating magnetic effects of current.
Q8 (Right-hand rule)
Right-hand thumb rule determines:
Answer: B
Thumb in current direction, curled fingers show magnetic field direction around wire — that's the right-hand thumb rule.
Q9 (Oersted)
If current in a wire is reversed, the compass needle deflection will:
Answer: C
Reversing current reverses magnetic field direction, so compass deflection reverses its sense.
Q10 (Rules)
Right-hand grip rule is used for:
Answer: B
Curl fingers along current in coil; thumb points toward the solenoid's north pole — right-hand grip rule for coils/solenoids.
Q11 (Oersted)
A compass placed above a horizontal wire carrying current eastward will point:
Answer: B
Field lines are circles around wire; compass aligns tangentially — direction given by right-hand rule (depends on which side it's placed).
Q12 (Rules)
Which hand rule gives direction of force on current-carrying conductor?
Answer: B
Fleming's left-hand rule (thumb = motion, forefinger = field, middle = current) gives direction of force on conductor in motor context.
Q13 (Straight wire)
Magnetic field near a long straight wire carrying current I at distance r is proportional to:
Answer: B
B ∝ I/r (exact B = μ₀I/2πr) — field increases with I and decreases with distance r.
Q14 (Straight wire)
Doubling the distance from a long wire reduces the field to:
Answer: B
Because B ∝ 1/r, doubling r halves B approximately for a long wire.
Q15 (Circular loop)
For a single circular loop of radius r carrying current I, field at centre is proportional to:
Answer: B
B at centre ≈ μ₀ I / (2 r) for a loop — inversely proportional to radius and directly to current.
Q16 (Circular loop)
If current in a circular loop is reversed, the direction of field at centre:
Answer: A
Reversing current reverses field direction (right-hand grip shows thumb direction changes).
Q17 (Loop)
Two identical loops carrying equal currents in same sense, placed coaxially close together, result in field at centre that is:
Answer: B
Fields from each loop add (vectorially) at centre if currents flow same way, strengthening total field.
Q18 (Field geometry)
Field lines inside a solenoid are:
Answer: C
Inside long solenoid, lines are nearly parallel and uniformly spaced indicating uniform field.
Q19 (Loop & wire)
Which produces a magnetic field similar to a bar magnet?
Answer: B
Coils and solenoids have north and south poles and external field resembling bar magnet.
Q20 (Experiment)
Which instrument can map magnetic field direction around a wire?
Answer: B
A compass needle aligns with local magnetic field, useful to trace field lines around conductor or coil.
Q21 (Calculation concept)
If current I in a long wire is increased, the magnetic field at a fixed r will:
Answer: B
B ∝ I/r, so increasing current increases magnetic field proportionally at that point.
Q22 (Concept)
Which factor does NOT affect magnetic field inside an ideal solenoid?
Answer: D
Ambient light has no effect on magnetic field; core material affects field via permeability, and n and I directly affect B = μ n I.
Q23 (Solenoid)
Magnetic field inside a long solenoid is given by:
Answer: B
Inside an ideal long solenoid B = μ₀ n I where n = turns per unit length; option A is for a circular loop at centre.
Q24 (Electromagnet)
Why is soft iron used as core in electromagnets?
Answer: B
Soft iron concentrates magnetic field (high permeability) and does not retain much magnetism (low retentivity), making it ideal for electromagnets.
Q25 (Electromagnet)
Which action increases strength of an electromagnet most effectively?
Answer: B
More turns increase n and iron core raises permeability; both increase B (B ∝ nI and core enhances field).
Q26 (Solenoid)
If a solenoid is disconnected from supply, the core (soft iron) will:
Answer: B
Soft iron loses induced magnetism rapidly when current stops — useful for switchable electromagnets.
Q27 (Applications)
Electromagnets are used in which of the following?
Answer: D
Electromagnets have many applications including bells, speakers, cranes — switchable and controllable field makes them versatile.
Q28 (Design)
To get stronger field in a given solenoid without changing current, you should:
Answer: A
Increasing n (turn density) increases B (B = μ₀ n I); removing core would weaken field.
Q29 (Practical)
Which property of core material reduces residual magnetism?
Answer: B
Low coercivity (soft magnetic materials) means they demagnetise easily, leaving little remanence after current stops.
Q30 (Concept)
The field outside a long solenoid resembles that of:
Answer: B
Outside, solenoid field lines emerge from one end and enter the other, like a bar magnet’s external field.
Q31 (Force)
Magnitude of force on a straight conductor of length L carrying I in perpendicular magnetic field B is:
Answer: B
F = B I L (when conductor is perpendicular to uniform field); if at angle θ, F = B I L sinθ.
Q32 (Motor)
Fleming's left-hand rule helps find:
Answer: B
Left-hand rule (Fleming) gives motion (thumb), field (forefinger), current (middle) for motors.
Q33 (Motor)
If current through a conductor is doubled in same B and L, force becomes:
Answer: C
F ∝ I, so doubling I doubles force (F = BIL).
Q34 (Motor design)
The commutator in a DC motor is used to:
Answer: B
Commutator (split-ring) reverses coil current each half rotation, keeping torque direction consistent for continuous rotation.
Q35 (Practical)
What increases torque of a motor for given field and supply?
Answer: B
Torque ∝ magnetic moment (N I A) × B; increasing coil area or current increases torque.
Q36 (Direction)
Reversing both field and current in a motor results in:
Answer: B
Reversing both flips the two inputs in Fleming’s rule, leaving force direction unchanged (two negatives cancel).
Q37 (Application)
Which of these appliances commonly uses electric motor principle?
Answer: A
Electric fan uses motor to convert electrical energy to mechanical rotation; bulb converts electrical energy to light/heat.
Q38 (Calculation)
Force on 0.2 m conductor carrying 3 A in 0.5 T field (perpendicular) is:
Answer: A
F = BIL = 0.5 × 3 × 0.2 = 0.3 N.
Q39 (Motor)
In a motor, brushes make contact with:
Answer: B
Brushes press on commutator segments to supply current to the rotating coil while allowing rotation.
Q40 (Design)
Why are motor armatures wound with many turns instead of one long conductor?
Answer: A
Multiple turns increase total conductor length in field, increasing force and torque without impractical single long conductor shape.
Q41 (Fleming)
Fleming's right-hand rule is used to find direction of:
Answer: A
Right-hand rule: thumb = motion, forefinger = field, middle = induced current — used for generators.
Q42 (Application)
Which device converts mechanical energy to electrical using induction?
Answer: B
Generators use electromagnetic induction to produce emf when coils move in magnetic field.
Q43 (Practical)
A relay uses electromagnet to:
Answer: B
Relay coil (small current) energises electromagnet to pull contacts and switch larger currents isolatedly.
Q44 (Fleming)
Which finger in Fleming's left hand represents current?
Answer: C
In left-hand rule: thumb = motion/force, forefinger = field, middle = current.
Q45 (Application)
Which of the following uses electromagnetic principle for lifting heavy metal?
Answer: B
Electromagnet cranes use switchable strong magnetic fields to lift scrap metal.
Q46 (Direction)
Applying Fleming's right-hand rule: Thumb is motion, forefinger field; middle finger shows:
Answer: A
Middle finger indicates direction of induced current in generator context (right-hand rule).
Q47 (Practical)
How can you increase induced emf in a coil for a generator?
Answer: B
Induced emf ∝ rate of change of flux × number of turns — increase speed, flux change or turns to raise emf.
Q48 (Safety)
Which precaution is important while experimenting with electromagnets?
Answer: A
High current can overheat coils; use proper insulation, current limits and cooling. Avoid touching live parts.
Q49 (Induction)
Electromagnetic induction is the production of emf due to:
Answer: B
Changing magnetic flux (by motion or field change) induces emf in a circuit — core principle of generators.
Q50 (Lenz)
Lenz's law states that induced current will flow in a direction to:
Answer: B
Lenz's law: induced current opposes the change in magnetic flux producing it, consistent with energy conservation.
Q51 (Experiment)
When a magnet is moved toward a coil connected to a galvanometer, the needle deflects. If magnet held stationary, needle:
Answer: B
Induced emf occurs only during change in flux; when stationary no change → needle returns to zero.
Q52 (Eddy currents)
Dropping a magnet through a conducting (non-magnetic) tube causes it to fall slowly due to:
Answer: B
Changing flux induces eddy currents in tube walls; their magnetic effect opposes motion (Lenz), slowing the magnet.
Q53 (Generator)
Increasing the speed of rotation in a coil (generator) leads to:
Answer: B
Faster rotation increases rate of change of flux → larger induced emf (brighter output if load allows).
Q54 (Transformer concept)
Transformers (conceptually) operate on which principle?
Answer: B
Transformers use changing magnetic flux in primary to induce emf in secondary — electromagnetic induction (AC required).
Q55 (Practical)
To make a simple generator produce larger emf without increasing speed, you could:
Answer: B
More turns or stronger magnetic field increase induced emf for same flux change rate.
Q56 (Lenz)
Which principle explains why induced currents oppose motion causing damping (e.g., eddy current brakes)?
Answer: B
Lenz's law predicts direction of induced currents so that their field opposes motion, producing braking effect.
Q57 (Observation)
When a coil is rapidly moved in and out of a magnetic field, the induced current is:
Answer: B
Induced current appears while magnetic flux is changing (when moving); stationary coil with steady flux sees no induced current.
Q58 (Calculation idea)
To increase induced emf in coil, which change helps most?
Answer: B
Induced emf ∝ rate of change of flux; increasing speed enhances rate and increases emf.
Q59 (Application)
Which of the following is a direct application of electromagnetic induction?
Answer: B
Generators convert mechanical motion to electrical energy by changing magnetic flux through coils (electromagnetic induction).
Q60 (Summary)
Which statement best summarises Chapter 12?
Answer: B
Chapter links electricity and magnetism: current produces magnetic fields (Oersted), and changing magnetic fields induce emf (Faraday/Lenz) — foundation for motors, generators, electromagnets.