Q1: What is a magnetic field?
Answer
A magnetic field is the region around a magnet or current where magnetic forces are experienced; represented by field lines.
Magnetic Effects of Electric Current – Very Short Answer Type Questions
CBSE • NCERT • Class 10
Physics — Chapter 12: Magnetic Effects of Electric Current — 50 Very Short Answer Questions
Topic-wise very short questions (VSA) with concise answers — ideal for quick revision and board exam practice.
Use:
Rapid revision, quick quizzes, and classroom warm-ups aligned to NCERT.
Rapid revision, quick quizzes, and classroom warm-ups aligned to NCERT.
- Basic magnetism & field lines (Q1–Q6)
- Magnetic field due to current & rules (Q7–18)
- Force on current-carrying conductor & motor (Q19–30)
- Electromagnets & solenoids (Q31–38)
- Electromagnetic induction basics & applications (Q39–46)
- Mixed quick facts & safety (Q47–50)
Basics & Magnetic Field Lines (Q1–Q6)
Q2: Which direction do magnetic field lines outside a magnet run?
Answer
Outside a magnet, field lines run from the north pole to the south pole.
Q3: Do magnetic field lines cross each other?
Answer
No — magnetic field lines never cross; crossing would imply two directions of field at same point.
Q4: What does the density of field lines indicate?
Answer
Density indicates field strength — closer lines mean stronger magnetic field.
Q5: How are field lines inside a magnet directed?
Answer
Inside a magnet, field lines move from the south pole towards the north pole, completing closed loops.
Q6: Give one way to visualize magnetic field lines experimentally.
Answer
Use iron filings sprinkled around a magnet; they align along the field lines and reveal the pattern.
Magnetic Field due to Current & Direction Rules (Q7–Q18)
Q7: Who discovered that current produces magnetic effects?
Answer
Hans Christian Oersted discovered that an electric current deflects a compass needle, showing magnetic effects of current.
Q8: What is the pattern of magnetic field around a straight current-carrying conductor?
Answer
The field consists of concentric circles centered on the wire, lying in planes perpendicular to the wire.
Q9: State the right-hand thumb rule.
Answer
If the thumb of the right hand points in the current direction, the curl of the fingers shows the magnetic field direction around the wire.
Q10: How does field strength vary with distance from a straight wire?
Answer
Field strength decreases with distance — approximately inversely proportional to distance (B ∝ 1/r) for a long straight wire.
Q11: How does magnetic field depend on current?
Answer
Magnetic field is directly proportional to current: increasing current increases the magnetic field strength.
Q12: What is the magnetic field pattern at the centre of a circular current loop?
Answer
At the centre, field lines are nearly straight and perpendicular to the plane of the loop; direction given by right-hand rule for loops.
Q13: What is a solenoid?
Answer
A solenoid is a long coil of many turns of wire; when current flows, it produces a magnetic field similar to that of a bar magnet.
Q14: How is the field inside a solenoid compared to outside?
Answer
Inside a long solenoid, the field is nearly uniform and strong; outside it is weaker and resembles that of a bar magnet.
Q15: What is the relation for magnetic field inside an ideal solenoid?
Answer
B = μ₀ n I (where n = number of turns per unit length, I is current, μ₀ is permeability of free space).
Q16: How is the direction of field in a solenoid determined?
Answer
Use right-hand grip rule: curl fingers in direction of current in turns; thumb points toward the solenoid’s north pole (field direction).
Q17: What instrument shows magnetic field direction around a conductor?
Answer
A small compass needle placed near the conductor shows the direction of the magnetic field by its deflection.
Q18: Give a single-word effect observed when a current is switched on near a compass.
Answer
Deflection.
Force on Current-carrying Conductor & Motor (Q19–Q30)
Q19: State Fleming's left-hand rule in brief.
Answer
Stretch thumb, forefinger and middle finger at right angles: Forefinger = magnetic field, Second(middle) = current, Thumb = motion (force) — used for motors.
Q20: What formula gives magnitude of force on a straight conductor of length L carrying current I in magnetic field B (perpendicular)?
Answer
F = B I L.
Q21: If a conductor of length 0.2 m carries 5 A in a 0.3 T field (perpendicular), what is force? (quick compute)
Answer
F = BIL = 0.3 × 5 × 0.2 = 0.3 N.
Q22: What causes rotation of the coil in an electric motor?
Answer
Forces on opposite sides of the current-carrying coil produce a torque that rotates the coil in the magnetic field.
Q23: What is the role of commutator in a DC motor?
Answer
The commutator reverses the direction of current in the coil every half rotation so that torque direction remains the same and rotation continues.
Q24: How are brushes used in a motor?
Answer
Brushes provide sliding electrical contact between stationary external circuit and rotating commutator segments, supplying current to the coil.
Q25: What happens to force if current direction is reversed?
Answer
The direction of force reverses (F ∝ I), so motion direction reverses accordingly.
Q26: How does increasing current affect motor torque?
Answer
Torque increases because force F = BIL grows with current I, producing larger turning effect.
Q27: Name a practical device that works on motor principle.
Answer
Electric fan (or washing machine motor, blender, etc.).
Q28: What is Lorentz force in one line (Class 10 view)?
Answer
Force experienced by a charge moving in a magnetic field; for current in conductor it gives F = BIL.
Q29: If length of conductor in field doubles, what happens to force (all else same)?
Answer
Force doubles, since F ∝ L.
Q30: Give one method to increase force on a conductor in given B and I.
Answer
Increase length of conductor in the field, or place more turns in the coil, or increase current I.
Electromagnets & Solenoids (Q31–Q38)
Q31: What is an electromagnet?
Answer
An electromagnet uses a coil carrying current around a soft iron core to produce a controllable strong magnetic field.
Q32: Why is soft iron used as core in electromagnets?
Answer
Soft iron is easily magnetised and demagnetised, giving strong temporary magnetism without retaining it permanently.
Q33: How can strength of an electromagnet be increased?
Answer
Increase number of turns, increase current, use a better core material, or make turns closer (increase n or I).
Q34: How does a solenoid behave like a bar magnet?
Answer
A current-carrying solenoid produces a near-uniform internal field and has distinct north and south poles, similar to a bar magnet.
Q35: Mention one application of electromagnets in industry.
Answer
Electromagnets are used in cranes to lift scrap iron and steel in scrapyards.
Q36: What happens to an electromagnet when current is switched off?
Answer
It loses its magnetism (becomes non-magnetic or weakly magnetic) as the magnetising current stops.
Q37: Define turns per unit length (n) in a solenoid.
Answer
n = N/L where N is total number of turns and L is length of the solenoid; it appears in B = μ₀ n I.
Q38: How does field inside a tightly wound solenoid compare to a loosely wound one (same current)?
Answer
Tightly wound solenoid (higher n) produces a stronger magnetic field inside than a loosely wound one.
Electromagnetic Induction & Applications (Q39–Q46)
Q39: What is electromagnetic induction (short)?
Answer
It is the process where a changing magnetic field induces an emf (and current) in a nearby conductor.
Q40: State Fleming's right-hand rule purpose in one line.
Answer
It gives the direction of induced current when a conductor moves in a magnetic field (used for generators).
Q41: Name a device that works on electromagnetic induction.
Answer
Electric generator (or transformer, though transformers are beyond class 10 details).
Q42: What happens to induced emf when relative speed between magnet and coil increases?
Answer
Induced emf increases because the rate of change of magnetic flux increases.
Q43: If magnetic flux through a coil becomes zero from a finite value rapidly, is an emf induced?
Answer
Yes — the rapid change in flux induces an emf in the coil.
Q44: Give one household application of electromagnetic induction principle.
Answer
Induction cooktops / electric generators in power stations / wireless chargers (basic idea).
Q45: What is Lenz's law in one sentence (class 10 view)?
Answer
The direction of induced current is such that it opposes the change in magnetic flux that produced it.
Q46: How does number of turns affect induced emf in a coil?
Answer
Induced emf is proportional to number of turns — more turns → larger induced emf for same flux change.
Quick Facts, Applications & Safety (Q47–Q50)
Q47: Why should experiments with coils limit current?
Answer
To prevent overheating of the coil and avoid insulation damage or burns; high currents produce heat.
Q48: Give one use of electromagnets in medical equipment.
Answer
Electromagnets are used in MRI (magnetic resonance imaging) machines (conceptual; advanced device).
Q49: What is a practical sign that a wire is producing a magnetic field?
Answer
A nearby compass needle deflects when current flows in the wire.
Q50: One quick revision tip for diagrams in this chapter?
Answer
Label poles, current direction, and field-line directions clearly; use arrowheads on field lines and show compact spacing near poles for stronger field.