Magnetic Fields
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| magnetic field/mæɡˈnetɪk fiːld/ | từ trường |
A compass needle always finds north
- Set a compass anywhere and its needle swings to point north, guided by something unseen.
- That something is a magnetic field 磁场 — Earth's, filling the space around it.
- Every magnet has one, reaching out invisibly to push and pull other magnets.
- Learning to picture it is the first step into all of magnetism.
Poles and forces
- Every magnet has a north pole and a south pole — they always come in pairs.
- Like poles repel; opposite poles attract — the magnetic version of the charge rule.
- You can never isolate a single pole: cut a magnet and each piece has both N and S.
- The poles are where the magnet's field is strongest.
Magnets attract and repel
Bring two magnets together and see whether they attract or repel and how the field looks.
Two north poles are brought together. They:
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Like poles repel, just as like charges do.
Magnetic poles always come in ____.
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Every magnet has both a north and a south pole.
Reading field lines
- Field lines show the field's direction — the way a compass north would point.
- Outside a magnet they run from the north pole to the south pole.
- Where lines are closer together, the field is stronger (near the poles).
- Lines never cross, and they always form closed loops.
Outside a magnet, field lines point:
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Outside a magnet, field lines run from the north pole to the south pole.
Select all true statements about magnetic field lines.
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Field lines run N → S, crowd near strong field, and never cross. They form closed loops, not single poles.
Earth is a giant magnet
- Earth behaves like a huge bar magnet, which is why compasses work.
- Its field also shields us from harmful particles streaming from the Sun.
- Magnetic materials like iron can be magnetised to make their own field.
- The magnetic field, like the electric field, is a vector at every point.
You can cut a bar magnet to obtain a single, isolated north pole.
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Poles always come in pairs; each piece of a cut magnet has both N and S.
Earth behaves like a giant bar magnet, which is why compasses work.
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Earth's magnetic field aligns compass needles toward the poles.
Magnetic poles always come in pairs — you can never have a lone north or south pole (unlike electric charge, where a single + or − exists). Cut a magnet in half and each half instantly has both an N and an S pole.
You bring the north pole of one magnet near the north pole of another. What happens?
- Like poles repel, so the magnets push apart.
- Turn one around so N faces S, and they attract instead.
A magnetic field surrounds every magnet, with a north and south pole (always in pairs). Like poles repel, opposites attract. Field lines run N → S outside the magnet, are denser where the field is stronger, and never cross. Earth itself is a giant magnet.
Write from 8 poles
- One bar magnet is snapped into 4 pieces.
- How many magnetic poles are there afterwards?
A single bar magnet is snapped across its length into 4 separate pieces. How many magnetic poles do those pieces have in total?
Four pieces with two poles each make 8.
How many poles are there after the snap?
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Each fragment keeps a north and a south.