Answer: The net direction of the compass needle depends on vector sum of magnetic fields produced by the magnet and the current. If the wire’s field at the compass is stronger than the magnet’s local field, the needle aligns with the wire’s field; otherwise the magnet dominates. Field strength from a straight wire is B ∝ I/r (decreases with distance), so increasing current or bringing the wire closer can make its field dominate.

Answer: Use the right-hand thumb rule: point the right thumb in direction of current; the curl of fingers gives the direction of magnetic field lines around the wire. Determine the field direction at the compass location (tangent to a circle centered on the wire) to predict whether the needle deflects clockwise or anticlockwise.

Answer: Each wire produces circular magnetic field lines. For two parallel currents in same direction, the field at each wire due to the other is such that the force between them is attractive (from F = I L × B directions via Fleming’s left-hand rule or Ampère’s force law). Opposite currents produce fields resulting in repulsive force. This effect underlies the definition of ampere in terms of force between conductors.

Answer: Inside a long solenoid fields from many turns add constructively producing an almost uniform, strong magnetic field along the axis (B ∝ nI). Outside, fields from turns largely cancel and spread out, giving weaker field. Hence the compass shows strong alignment inside and weak deflection outside.

Answer: For a long straight wire B = μ₀I/(2πr) — field inversely proportional to distance r. Doubling r roughly halves B, matching observation. This inverse relation holds when wire is long compared to measurement distances.

Answer: Field at loop centre B ≈ μ₀I/(2r) for a single loop — inversely proportional to radius. Smaller radius concentrates the field at centre giving larger B if current unchanged.

Answer: B inside solenoid ∝ nI (n = turns per unit length). More turns per length increases n, thus B increases for same I. Tighter winding raises n, producing stronger internal field.

Answer: Reversing current reverses direction of magnetic field; north and south poles swap. Use right-hand grip rule: curl fingers in current direction — thumb points to north pole. Reverse current and thumb points opposite way, indicating swapped poles.

Answer: Increasing current I raises B linearly (B ∝ nI). Using a ferromagnetic (soft iron) core greatly increases B due to high permeability concentrating field. Trade-offs: higher current causes heating and power use; core choice risks hysteresis/retained magnetism (soft iron mitigates). Safety and power considerations limit maximum practical current.

Answer: Force magnitude F = B I L. To increase F when B and L are fixed, increase current I (if safe). Alternatively increase effective conductor length in field (use multiple turns or coil) or increase B (stronger magnets). But higher I may heat the conductor and require thicker wire or cooling.

Answer: When coil aligns, torque momentarily becomes zero. The commutator reverses current direction every half-turn, so forces on coil sides reverse appropriately and torque continues in same rotational sense after alignment, producing continuous rotation. Proper inertia and timing help the coil pass the zero-torque position; commutator ensures torque direction remains favorable.

Answer: Torque ∝ I (since F = BIL and torque is F×radius). Increasing supply voltage generally increases current (depending on load and resistance) thus increasing torque, but the relation is not universally linear because motor back-emf and load-dependent current complicate behavior. Correct statement: torque depends on current and magnetic field; voltage influences torque indirectly by affecting current.

Answer: Multiple turns effectively increase total length of conductor in the magnetic field (sum of lengths of turns), increasing total force and torque for the same current per turn. It allows higher torque with manageable conductor shapes and compact size. Also it increases induced emf and improves motor characteristics when appropriately connected.

Answer: Direction of force is given by Fleming’s left-hand rule (field, current, force). Reversing current flips middle finger; force direction reverses. Reversing field flips forefinger; force also reverses. Reversing both flips both fingers — the thumb (force) remains pointing same way (two negatives make a positive), so rotation direction is unchanged.

Answer: Electromagnets can be switched on/off by controlling current — crucial for releasing lifted scrap. They can provide stronger fields (using many turns and iron core) than comparable permanent magnets in same size. Soft iron core concentrates field and demagnetises quickly when current is off, allowing controlled pick-and-release operations.

Answer: The electromagnet in the relay uses small coil current to produce a magnetic field that pulls a mechanical contact closing the high-current circuit — the coil and contacts are electrically isolated. Mechanical switching allows small control signal to operate larger currents safely; design ensures contacts rated for load and coil current kept small for control electronics.

Answer: Residual magnetism (remanence) occurs if core material has hysteresis — some magnetisation persists. Use soft iron with low coercivity to minimise remanence; degaussing procedures or using appropriate core alloys (silicon steel) reduce residual magnetisation. Designing circuits to reverse or momentarily demagnetise can mitigate effects.

Answer: Moving magnet changes magnetic flux through cross-sections of the tube, inducing eddy currents in the conductive walls. By Lenz's law induced currents produce magnetic fields opposing the change in flux, creating magnetic braking force opposing magnet's motion. This retards the fall — the stronger the conductor or the magnetic field, the greater the braking effect.

Answer: When magnet approaches, magnetic flux through coil increases; galvanometer deflects in one direction indicating induced current opposing increase. When magnet is held stationary, flux stops changing and needle returns to zero. When magnet is withdrawn, flux decreases and induced current reverses direction (opposing decrease), producing opposite deflection. Lenz's law explains induced current direction in each phase.

Answer: Induced emf arises from changing magnetic flux; when magnet moves relative to coil flux changes and emf is induced, lighting the bulb briefly. When motion stops, flux is steady and no emf induced, so bulb goes out. Induced emf magnitude ∝ rate of change of flux — faster motion gives larger emf and brighter flash (assuming circuit can carry current).