All 7 short questions of 9th Class Physics Chapter 8, Magnetism, with exam-ready answers in the book's words. Punjab Board new syllabus.
Exam-ready answers. Learn the meaning, then write them in your own words.
Magnets that are magnets only while they are in the field of another magnet (or while a current flows), and lose their magnetism when it is removed. Example: soft iron, an electromagnet.
Magnets that keep their magnetism for a long time. They are found in nature or made from steel and special alloys (alnico, ferrite, neodymium) placed in a strong field.
The region around a magnet in which another magnet or a magnetic material experiences a magnetic force.
Imaginary lines drawn to represent a magnetic field. They follow the pattern of iron filings round a magnet, go from N to S outside the magnet, never cross, and are closest together where the field is strongest.
| Permanent magnets | Electromagnets |
|---|---|
| D.C. motors | Electric bells |
| A.C. and D.C. generators | Telephone receivers |
| Moving-coil loudspeakers | Magnetic relays and circuit breakers |
| Door catchers, compasses | Cranes, maglev trains |
A tiny region, about 0.1 mm across, in a ferromagnetic material in which the magnetic fields of about 10¹⁶ atoms point the same way. Each domain is strongly magnetised and acts as a small magnet with its own N and S poles.
A long current-carrying coil (a solenoid) produces a field like that of a bar magnet: one end acts as an N-pole and the other as an S-pole, and the field inside is strong and nearly uniform. The N end is found by the right-hand grip rule.
| Paramagnetic | Diamagnetic |
|---|---|
| The fields of the electrons' orbital and spin motions support each other | The fields of the orbital and spin motions cancel |
| Each atom acts as a tiny magnet (magnetic dipole) | The atom has no resultant field |
| Examples: aluminium, lithium | Examples: copper, bismuth, water |
