The rule to determine the direction of a current induced in a coil due to its rotation in a magnetic field is:

Correct — C, Fleming's Right-Hand Rule. A coil turning in a magnetic field cuts field lines, the flux through it changes, and an electromotive force is induced. That is a generator, and the generator rule is Fleming's right-hand rule: stretch the thumb, forefinger and middle finger of the right hand so that all three are at right angles to one another, point the forefinger along the magnetic field and the thumb along the motion of the conductor, and the middle finger then points along the induced current. The other three options each answer a different question. The right-hand thumb rule is about the field a current makes, not about a current a field makes: grip the wire with the right hand, thumb along the current, and the curled fingers give the direction of the circular field lines around it. Fleming's left-hand rule is the motor rule — forefinger for field, second finger for the current you supply, thumb for the force the conductor then feels. Hund's rule is not electromagnetism at all; it is the chemistry rule about how electrons occupy orbitals of equal energy. The one-line test is which way the causation runs. If motion produces current, use the right hand; if current produces motion, use the left.

• (a)Right-Hand Thumb Rule. — Also called Maxwell's corkscrew rule, it gives the direction of the magnetic field set up around a straight wire carrying a current. It says nothing about a current induced by movement.
• (b)Fleming's Left-Hand Rule. — The motor rule. It is used when a current-carrying conductor is placed in a magnetic field and you want the direction of the force on it. Here nothing is being driven — the coil is being turned and current is the output.
• (d)Hund's Rule. — A rule of atomic structure: electrons singly occupy each orbital of a subshell, with parallel spins, before any orbital is doubly occupied. It has no bearing on induced currents and is in the list only to catch a candidate matching on the word 'rule'.

Electromagnetic induction is Faraday's discovery that a changing magnetic flux through a circuit drives a current in it. Lenz's law fixes the direction: the induced current always flows so as to oppose the change that produced it, which is why a generator gets harder to turn as you draw more current from it. Fleming's right-hand rule is a hand mnemonic for that direction in the common case of a straight conductor moving across a field, and it agrees with Lenz's law in every case; it is not an independent physical law.

Papers test these rules by naming three of them together and letting candidates confuse the two Fleming rules. Keep them apart by the machine each belongs to. The left hand belongs to the motor — you feed in current and get out motion. The right hand belongs to the generator — you feed in motion and get out current. In both, the forefinger is the field; only the roles of thumb and middle finger swap. This paper family has been working steadily through the same NCERT exercise: CDS (I) 2025 asked which rule gives the field around a straight current-carrying conductor, and the NDA (II) 2025 paper asked which rule gives the force on such a conductor placed in a field. This item is the third part of the same question, so the three rules are worth learning as a set rather than one at a time.

• Fleming's right-hand rule: forefinger along the magnetic field, thumb along the motion of the conductor, middle finger gives the induced current.
• Fleming's left-hand rule: forefinger along the field, middle finger along the current supplied, thumb gives the force on the conductor.
• The right-hand thumb rule gives the direction of the magnetic field circling a straight current-carrying wire.
• Both Fleming rules require the three fingers to be held mutually at right angles.
• The right-hand rule is the mnemonic form of Lenz's law, which states that an induced current opposes the change that causes it.

• Swapping the two Fleming rules. Fix them by the machine: right hand generator, left hand motor.
• Using the right-hand thumb rule here because it has 'right hand' in the name; it answers a different question entirely.
• Forgetting that the three fingers must be mutually perpendicular — a rule applied with fingers held loosely gives the wrong answer as often as the right one.

Usually by naming the physical situation and asking for the rule, sometimes reversed — stating the rule's finger assignments and asking what the stretched finger predicts.

• practice — not a real PYQ

  In Fleming's left-hand rule, the thumb indicates the direction of which one of the following?

  • (a)The magnetic field
  • (b)The current in the conductor
  • (c)The force acting on the conductor
  • (d)The induced electromotive force

  Answer(c) The force acting on the conductor — the forefinger gives the field and the middle finger the current, so the thumb is left with the force, or motion.

• practice — not a real PYQ

  The direction of an induced current, as given by Fleming's right-hand rule, always agrees with which one of the following?

  • (a)Ohm's law
  • (b)Lenz's law
  • (c)Coulomb's law
  • (d)Ampere's circuital law

  Answer(b) Lenz's law — the induced current opposes the change in flux that produced it, and the right-hand rule is simply a convenient way of finding that direction.