Magnetism and Electromagnetism

According to Lenz’s law, the direction of induced emf is such that it opposes the change responsible for its production.

Whenever there is a change in the lines of force linked with the conductor, emf is induced in the conductor as long as the change lasts.

Field magnet is a strong horseshoe permanent magnet.

The alternating emf (or current) is that which changes in magnitude and direction periodically.

Direction of induced current produced by motion of a conductor in a magnetic field is given by Fleming's right hand rule.

Magnitude of induced emf is directly proportional to the strength of the inducing magnet, number of turns of coil and area of cross-section of coil.

Magnetic effect of electric current is used in a sensitive tester.

These machines, use a donut-shaped ring magnet with a cyclically increasing B field, but accelerate the particles by induction from the increasing magnetic field, as if they were the secondary winding in a transformer, due to the changing magnetic flux through the orbit.

Yes, it is correct. 

Lodestone is a naturally magnetized form of the mineral magnetite. It was the first magnetic material discovered and used in compasses. All other options - bar magnets, ball-ended magnets, and horseshoe magnets - are artificially manufactured magnets.

Magnets are materials that produce magnetic fields and attract ferromagnetic materials like iron, nickel, and cobalt. Option A correctly states that magnets attract iron pieces. The defining property of a magnet is its ability to attract certain metals.

A horseshoe magnet is bent into a U-shape, which brings both poles closer together to create a stronger magnetic field in the space between them. This design is commonly used in educational demonstrations and for lifting small metal objects. Bar magnets are straight, cylindrical magnets are round, and magnetic needles are thin compass-style magnets.

Non-magnetic materials like wood, plastic, glass, and paper are not attracted to magnets because they don't have unpaired electrons that can align with magnetic fields. Magnetic materials (iron, nickel, cobalt) are strongly attracted. All substances are not magnetic, and iron-fillings are actually magnetic, making them attracted to magnets.

A bar magnet has a rectangular shape - it's essentially a straight bar with two opposite magnetic poles at its ends. Circular would describe disc magnets, oval is not a standard magnet shape, and U-shape describes horseshoe magnets, not bar magnets. The rectangular bar shape is fundamental to its designation as a 'bar' magnet.

Every magnet has exactly two poles - a north pole and a south pole. This is fundamental to magnetism; you cannot have a magnet with only one pole (magnetic monopoles don't exist in ordinary matter). Even if you cut a magnet in half, each piece becomes a complete magnet with two poles. The two poles are always paired together.