Introduction to magnetism

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课程笔记

Magnetism as a Non-Contact Force

Magnetism is a non-contact force – it acts between objects that are not touching.
A contact force requires objects to be physically touching (e.g., friction).
Non-contact forces are caused by a field; for magnetism, it is a magnetic field.

Every magnet has a north pole and a south pole.

Magnetic Field Lines

Magnetic field lines point away from the North pole and towards the South pole.
The direction of a field line gives the direction of force on the North pole of another magnet.
Field lines are closer together where the field is stronger (near the poles).
Like poles repel; unlike poles attract.

Visualising Magnetic Fields

Sprinkle iron filings on paper placed over a bar magnet to see the field pattern.
Iron filings align along the field lines and cluster at the poles (strongest field).

Magnetic Metals

The three magnetic metals are iron, nickel, and cobalt.
Steel is magnetic because it contains iron.
Magnetic metals are attracted to permanent magnets but never repelled.

Magnetic materials (iron, steel, cobalt, nickel) are attracted to a magnet; non-magnetic materials (zinc, copper, gold, silver, magnesium, aluminium) are not.

Permanent Magnets

A permanent magnet (e.g., bar magnet) produces its own magnetic field.
A permanent magnet can be demagnetised by: heating, hitting with a hammer, or placing in a reversed magnetic field.

Compasses and toy trains are two examples of the use of permanent magnets.

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练习题

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1.Which of the following is a non-contact force?
Easy
- AMagnetism
- BFriction
- CAir resistance
- DTension
2.Magnetic field lines point away from the north pole and towards which pole?
Easy
- ASouth pole
- BNorth pole
- CEast pole
- DWest pole
3.Which of the following metals is magnetic?
Easy
- AIron
- BCopper
- CAluminium
- DGold
4.Two like poles of magnets will:
Easy
- ARepel each other
- BAttract each other
- CHave no effect
- DCancel each other
5.Which of the following statements about magnetic field lines is true?
Medium
- AThey are closer together where the field is stronger.
- BThey are closer together where the field is weaker.
- CThey point from south to north outside the magnet.
- DThey never form closed loops.
6.A bar magnet is placed under a sheet of paper and iron filings are sprinkled on top. Where will the iron filings concentrate most?
Easy
- AAt the poles
- BAt the centre
- CEvenly spread
- DAway from the magnet
7.Which of the following can demagnetise a permanent magnet?
Medium
- AHeating it
- BCooling it
- CPlacing it in a weak magnetic field
- DPainting it
8.Which of the following is true about magnetic metals?
Easy
- AThey are always attracted to a magnet.
- BThey are always repelled by a magnet.
- CThey can be either attracted or repelled.
- DThey are never affected by magnets.

更多题目

9.A student brings a bar magnet near a piece of steel. What will happen?
Easy
- AThe steel will be attracted to the magnet.
- BThe steel will be repelled by the magnet.
- CThe steel will become a permanent magnet.
- DNothing will happen.
10.Which of the following is NOT a way to demagnetise a permanent magnet?
Medium
- APlacing it in a strong magnetic field opposite to its own.
- BHeating it to a high temperature.
- CStroking it with another magnet.
- DDropping it repeatedly on a hard surface.
11.Two bar magnets are placed with their north poles facing each other. What is the force between them?
Easy
- ARepulsive
- BAttractive
- CNo force
- DAlternating
12.Which of the following correctly describes the magnetic field around a bar magnet?
Easy
- AIt is strongest at the ends and weaker in the middle.
- BIt is strongest in the middle and weaker at the ends.
- CIt is uniform throughout.
- DIt is zero outside the magnet.
13.A student places a bar magnet under a sheet of paper and sprinkles iron filings on top. Which pattern do the iron filings form?
Medium
- AThey form a pattern of lines curving from the north pole to the south pole, most concentrated at the poles.
- BThey form a pattern of straight lines from the north pole to the south pole.
- CThey form a random scatter across the paper.
- DThey concentrate only at the north pole.
14.A piece of steel is brought near the north pole of a bar magnet. What will happen?
Easy
- AThe steel will be attracted to the magnet.
- BThe steel will be repelled by the magnet.
- CThe steel will not be affected.
- DThe steel will become a permanent magnet.
15.A student has three unlabelled metal rods: one is iron, one is copper, and one is aluminium. Using only a bar magnet, how can the student identify the iron rod?
Medium
- AThe rod that is attracted to the magnet is iron.
- BThe rod that is repelled by the magnet is iron.
- CThe rod that does not interact with the magnet is iron.
- DThe rod that becomes magnetised temporarily is iron.
16.A bar magnet is cut into two equal pieces perpendicular to its length. What will happen to the magnetic properties of the pieces?
Medium
- AEach piece becomes a complete magnet with its own north and south pole.
- BOne piece becomes a north pole and the other becomes a south pole.
- CBoth pieces lose their magnetism.
- DThe pieces repel each other.
17.Which of the following statements about magnetic field lines is correct?
Medium
- AMagnetic field lines always form closed loops.
- BMagnetic field lines start at the south pole and end at the north pole.
- CMagnetic field lines are evenly spaced around a bar magnet.
- DMagnetic field lines can cross each other.
18.Which of the following is a magnetic metal?
Easy
- ANickel
- BCopper
- CAluminium
- DZinc
19.A student wants to demagnetise a permanent steel bar magnet. Which method will NOT demagnetise it?
Medium
- APlacing it in a strong magnetic field with the same polarity.
- BHeating it to a high temperature.
- CHitting it repeatedly with a hammer.
- DPlacing it in a reversed magnetic field.
20.Two bar magnets are placed with their north poles 5 cm apart. What is the force between them?
Easy
- ARepulsive
- BAttractive
- CNo force
- DFirst attractive then repulsive
21.A student hangs a bar magnet from a string so it can rotate freely. When the magnet comes to rest, which direction does its north pole point?
Medium
- ATowards the Earth's geographic north pole.
- BTowards the Earth's geographic south pole.
- CTowards the east.
- DTowards the west.
22.Which of the following correctly lists the three magnetic metals?
Easy
- AIron, nickel, cobalt
- BIron, steel, aluminium
- CCopper, nickel, cobalt
- DIron, copper, zinc
23.A bar magnet is placed under a piece of paper and iron filings are sprinkled on top. Where will the iron filings be most concentrated?
Easy
- AAt the ends (poles) of the magnet.
- BIn the middle of the magnet.
- CEvenly distributed across the paper.
- DOnly at the north pole.
24.A student uses a compass to map the magnetic field around a bar magnet. At a point near the north pole of the magnet, which direction does the compass needle point?
Medium
- AAway from the north pole.
- BTowards the north pole.
- CParallel to the magnet.
- DRandomly.
25.A student places a bar magnet under a sheet of paper and sprinkles iron filings on top. The iron filings form a pattern that shows the magnetic field. Which statement about the iron filings is correct?
Medium
- AThey concentrate most where the field is strongest, which is near the poles.
- BThey concentrate most where the field is weakest, which is near the middle.
- CThey form straight lines perpendicular to the magnet.
- DThey are repelled by the north pole and attracted to the south pole.
26.What is the direction of magnetic field lines around a bar magnet?
Easy
- AFrom north pole to south pole outside the magnet
- BFrom south pole to north pole outside the magnet
- CFrom north pole to south pole inside the magnet
- DThey are circular and do not have a specific direction
27.A student has four metal rods: iron, copper, aluminium, and nickel. Using only a bar magnet, how can the student identify the magnetic metals?
Medium
- ABring the magnet near each rod; the ones that are attracted are iron, nickel, and possibly steel if present.
- BBring the magnet near each rod; the ones that are repelled are magnetic.
- CThe magnet will attract only iron and nickel, not aluminium or copper.
- DAll metals will be attracted to the magnet because all metals are magnetic.
28.A bar magnet is placed on a table with its north pole pointing north. A student places a compass near the south pole of the magnet. Which direction will the compass needle point?
Medium
- AThe north pole of the compass needle will point towards the south pole of the magnet.
- BThe south pole of the compass needle will point towards the south pole of the magnet.
- CThe compass needle will align with Earth's magnetic field and point north.
- DThe compass needle will spin randomly because it is too close to the magnet.
29.Which of the following methods can demagnetise a permanent magnet?
Easy
- AHeating it strongly
- BCooling it in liquid nitrogen
- CStoring it in a magnetic field
- DPainting it with a non-magnetic coating
30.A bar magnet is cut into two equal pieces perpendicular to its length. What happens to the magnetic properties of the pieces?
Medium
- AEach piece becomes a complete magnet with its own north and south poles.
- BThe pieces lose all magnetism.
- COne piece becomes a north pole only, the other a south pole only.
- DThe pieces remain magnetic but only have one pole each.
31.Magnetic field lines point away from which pole and towards which pole?
Easy
- AAway from north, towards south
- BAway from south, towards north
- CAway from north, towards north
- DAway from south, towards south
32.Is magnetism a contact force or a non-contact force?
Easy
- ANon-contact force
- BContact force
- CBoth
- DNeither
33.Which of the following statements is true?
Easy
- ACobalt is attracted to a bar magnet.
- BCopper is attracted to a bar magnet.
- CIron is repelled by a bar magnet.
- DMagnetic field lines point away from a south pole and towards a north pole.
34.What does the closeness of magnetic field lines indicate?
Easy
- AThe field is stronger where lines are closer together.
- BThe field is weaker where lines are closer together.
- CThe field is uniform regardless of line spacing.
- DThe lines indicate the direction of the south pole.
35.What happens when two like poles of magnets are brought near each other?
Easy
- AThey repel.
- BThey attract.
- CNothing happens.
- DThey become demagnetised.
36.Which of the following is NOT a method to demagnetise a permanent magnet?
Easy
- APlacing it in a strong magnetic field in the same direction
- BHeating it
- CHitting it with a hammer
- DPlacing it in a reversed magnetic field
37.A student sprinkles iron filings on a paper placed over a bar magnet. Where will the iron filings be most concentrated?
Easy
- AAt the poles of the magnet
- BAt the centre of the magnet
- CEvenly spread over the paper
- DAway from the magnet
38.A student hangs a bar magnet from a string so it can rotate freely. When the magnet comes to rest, its north pole points north. What does this indicate about the Earth?
Medium
- AThe Earth has a magnetic field with a magnetic south pole near the geographic North Pole.
- BThe Earth has a magnetic field with a magnetic north pole near the geographic North Pole.
- CThe Earth does not have a magnetic field; the magnet aligns with the stars.
- DThe Earth's magnetic field is too weak to affect the magnet.
39.A student has four metal rods: iron, copper, nickel, and aluminum. Using only a bar magnet, how can the student identify which rods are magnetic?
Easy
- ABring the magnet near each rod; the rods that are attracted are magnetic.
- BBring the magnet near each rod; the rods that are repelled are magnetic.
- CTouch the magnet to each rod; the rods that become warm are magnetic.
- DWeigh each rod; the heavier ones are magnetic.
40.A bar magnet is placed under a sheet of paper and iron filings are sprinkled on top. The iron filings form a pattern. Which statement about the pattern is correct?
Easy
- AThe filings are most concentrated at the poles, where field lines are closest together.
- BThe filings are most concentrated at the center of the magnet, where field lines are densest.
- CThe filings form straight lines parallel to the magnet.
- DThe filings are evenly distributed across the paper.
41.Magnetic field lines point away from the north pole and towards the south pole.
Easy
True or false?
42.The closer together the magnetic field lines, the weaker the field.
Easy
True or false?
43.Which of the following are magnetic metals? (Select all that apply)
Easy
- AIron
- BNickel
- CCopper
- DCobalt
- EAluminium
44.Magnetic field lines point away from a south pole and towards a north pole.
Easy
True or false?
45.Arrange the following steps to demagnetise a permanent magnet in the correct order:
Medium
- Place the magnet in a reversed magnetic field
- Heat the magnet strongly
- Allow the magnet to cool
- Hit the magnet with a hammer
46.Match each metal to whether it is magnetic or not.
Easy
- Iron
- Copper
- Nickel
- Aluminium
- Magnetic
- Not magnetic
47.Arrange the following steps to demagnetise a permanent magnet in the correct order from first to last. (Steps: heat the magnet, let it cool, hammer it while cooling)
Medium
- Heat the magnet until red hot
- Hammer the magnet while it cools
- Let the magnet cool in a reversed magnetic field
48.Which of the following are methods to demagnetise a permanent magnet? (Select all that apply)
Medium
- AHeating it strongly
- BHitting it with a hammer
- CPlacing it in a reversed magnetic field
- DStoring it with a keeper
- ECooling it in liquid nitrogen
49.Magnetic field lines point away from the south pole and towards the north pole.
Easy
True or false?
50.Which statement about the magnetic field around a bar magnet is correct?
Medium
- AThe field lines are straight and parallel near the poles.
- BThe field lines are closer together near the poles, indicating a stronger field.
- CThe field lines are evenly spaced around the magnet.
- DThe field lines point from the south pole to the north pole inside the magnet.
51.Complete the sentence: Magnetic field lines point away from the ___ pole and towards the ___ pole.
Easy
Magnetic field lines point away from the ____ pole and towards the ____ pole.
52.Explain why magnetic field lines are closer together near the poles of a bar magnet.
Medium
53.Complete the sentence:
Easy
The three magnetic metals are ____, ____, and ____.
54.A bar magnet has two poles. How many poles does each piece have if the magnet is cut into two equal pieces perpendicular to its length?
Medium
55.State whether magnetism is a contact or non-contact force.
Easy
56.Explain why a piece of iron is attracted to a bar magnet but a piece of copper is not.
Hard
57.A bar magnet has two poles. How many poles does each piece have if the magnet is cut into two equal pieces perpendicular to its length?
Medium
- A2
- B1
- C3
- D4

复习笔记

## Introduction to Magnetism - **Magnetism is a non-contact force** – it acts between objects that are not touching, caused by a magnetic field. - **Magnetic field lines** show the direction and strength of the field: - They point **away from the North pole** and **towards the South pole**. - The direction gives the force on the North pole of another magnet. - **Closer lines = stronger field** (strongest at the poles). - **Like poles repel, unlike poles attract.** - **Magnetic metals** (attracted but never repelled): **iron, nickel, cobalt**. Steel (contains iron) is also magnetic. Other metals (e.g., copper) are not. - **Demagnetisation**: heat, hammering, or reversed magnetic field. - **Visualising fields**: sprinkle iron filings on paper over a magnet – they align along field lines, concentrating at poles.

Non-contact force: A force that acts between objects not physically touching, caused by a field (e.g., magnetism).
Magnetic field: A region around a magnet where magnetic forces act, represented by field lines.
Magnetic field lines: Lines that show the direction and strength of a magnetic field; point away from North pole and towards South pole; closer lines indicate stronger field.
Pole: The ends of a magnet where the magnetic field is strongest; either North or South.
Like poles repel, unlike poles attract: Two North poles or two South poles push apart; a North and South pole pull together.
Permanent magnet: A magnet that produces its own magnetic field (e.g., bar magnet).
Magnetic metals: Iron, nickel, cobalt (and steel) – attracted to magnets but never repelled.
Demagnetisation: Process of removing magnetism by heating, hammering, or applying a reversed magnetic field.
Iron filings: Small pieces of iron used to visualise magnetic field lines.

闪卡

What type of force is magnetism?

Magnetism is a non-contact force.

What is a contact force?

A contact force acts when two objects are physically touching each other.

What is a non-contact force?

A non-contact force acts between objects that are not touching each other.

What causes non-contact forces?

Non-contact forces are caused by a field.

What are the poles of a bar magnet?

A bar magnet has a north pole and a south pole.

Which direction do magnetic field lines point?

Magnetic field lines point away from the North pole and towards the South pole.

What do magnetic field lines indicate about force direction?

The field lines give the direction of force on the North pole of another magnet.

What is the rule for magnetic attraction and repulsion?

Like poles repel. Unlike poles attract.

Where is the magnetic field strongest around a bar magnet?

The magnetic field is strongest near the ends (poles) of the bar magnet.

How can you tell the magnetic field is stronger near the poles?

The magnetic field lines are closer together near the poles.

What is a permanent magnet?

A permanent magnet produces its own magnetic field.

Name the three magnetic metals.

The three magnetic metals are iron, nickel, and cobalt.

Is steel magnetic? Why?

Yes, steel is magnetic because it contains iron.

Are non-magnetic metals attracted or repelled by permanent magnets?

Non-magnetic metals are neither attracted nor repelled; only magnetic metals are attracted.

Can a permanent magnet repel a magnetic metal?

No, magnetic metals are attracted by permanent magnets, never repelled.

How can a permanent magnet be demagnetised?

By heating it, hitting it with a hammer, or placing it in a reversed magnetic field.

How can you visualise the magnetic field around a bar magnet?

By placing a bar magnet under a piece of paper and sprinkling iron filings on top.

What do iron filings show about the magnetic field?

They arrange themselves in the shape of the field and are most attracted to the poles (strongest field).

True or false: Cobalt is attracted to a bar magnet.

True.

True or false: A north pole repels another north pole.

True.

True or false: Copper is attracted to a bar magnet.

False.

True or false: A north pole attracts a south pole.

True.

True or false: The closer together the magnetic field lines, the stronger the field.

True.

True or false: Iron is repelled by a bar magnet.

False.

True or false: Magnetic field lines point away from a south pole and towards a north pole.

False.

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