Grade 10 general science – Magnetism and electromagnetic induction Quiz

A permanent magnet is made of material whose atomic magnetic domains remain aligned, producing a steady magnetic field without any applied current. The other options describe temporary magnetisation or electromagnets.

Opposite magnetic poles attract while like poles repel. Magnetic monopoles (isolated single poles) have not been found in ordinary materials.

Magnetic field lines emerge from the north pole, curve through the surrounding space, and enter the south pole; they form closed loops continuing through the magnet.

Iron is ferromagnetic and is strongly attracted to magnets. Copper and aluminium are nonmagnetic (weakly affected) and plastic is non-magnetic.

Magnetisation occurs when the microscopic magnetic domains in iron align, producing a net macroscopic magnetic field.

A compass needle is itself a small magnet; it aligns with the Earth's magnetic field, so it points approximately to the magnetic north.

Magnetic field strength of an electromagnet increases with current and with more coil turns and a soft iron core. Increasing current increases the magnet's strength.

A long solenoid produces an approximately uniform magnetic field inside, directed along the axis; outside the field is weaker and less uniform.

Electromagnetic induction is Faraday's discovery that a changing magnetic flux through a circuit induces an emf and possibly a current in the conductor.

Faraday's law states induced emf is proportional to the rate of change of magnetic flux; faster change produces larger induced emf.

Lenz's law states the induced current creates a magnetic effect opposing the original change in flux, conserving energy and obeying Faraday's law with a negative sign.

Pushing the magnet faster increases the rate of change of magnetic flux through the coil, producing a larger induced current.

Generators convert mechanical energy to electrical energy by rotating coils in magnetic fields, inducing emf via electromagnetic induction. Transformers change voltage but need an alternating current source.

An ideal transformer uses electromagnetic induction between two coils on a core; the ratio of turns determines whether voltage is stepped up or down.

Fleming's left-hand rule is used for motors to find the direction of force on a current-carrying conductor in a magnetic field. The right-hand rule is for generators or positive charges.

Induced emf depends on the rate of change of magnetic flux; increasing the magnetic field strength increases flux change during rotation and thus the emf.

Laminations break up paths for eddy currents in the core, reducing energy losses and heating. A solid core would allow large eddy currents and greater losses.

Φ = B A cosθ: at θ = 0° cosθ = 1 gives maximum flux; at θ = 90° cosθ = 0 so flux becomes zero.

The SI unit of magnetic flux density (B) is the tesla (T). Weber measures magnetic flux, volt measures emf, and ampere measures current.

Moving the magnet toward or away changes the magnetic flux through the coil, inducing a current whose direction depends on whether the flux increases or decreases; the galvanometer shows this.

Eddy currents circulate within conductors exposed to changing magnetic fields; because of the material's resistance they produce heating and represent energy losses.

As the magnet falls, changing flux induces eddy currents in the tube that create magnetic fields opposing the magnet's motion, slowing its fall—this is Lenz's law.

A charged particle moving with velocity v through a magnetic field B experiences a force given by F = q(v × B), perpendicular to both v and B.

Voltage ratio equals turns ratio: Vsecondary = (Nsecondary/Nprimary) × Vprimary = (200/100) × 120 V = 240 V, so this is a step-up transformer.

Incandescent bulbs produce light by resistive heating of a filament, not by electromagnets. The other examples use electromagnets or magnetic fields.

While the total length changes with number of turns (affecting resistance), wrapping tight per se does not change the wire's resistance; the resistance depends on length, cross-sectional area, and material.

Soft iron has high permeability and low retentivity, so it becomes strongly magnetised with current and loses magnetism quickly when current is removed—ideal for electromagnets used on and off.