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Date: 2015-10-07; view: 468.

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PERMANENT MAGNET

Lodestone (also called ________) is a naturally-occurring permanent magnet mineral. _______ means that the material maintains a magnetic field with no external help. The characteristic of any magnetic material to do so is called ________.

Unlike electric charges, magnetic objects possessed two poles of opposite effect, denoted "north" and "south" after their self-orientation to the _______. As Peregrinus found, it was impossible to _______ one of these poles by itself by cutting a piece of lodestone in half: each resulting piece possessed its own pair of _______. Like electric charges, there were only two types of poles to be found: north and south (by analogy, _______ and negative). Just as with electric charges, same poles _______ one another, while opposite poles _______. This force, like that caused by static ________, could even pass through objects such as paper and wood with little effect upon strength.

________ materials are easily magnetized. __________ materials are magnetized with more difficulty. ________ materials actually tend to repel external magnetic fields by magnetizing in the opposite direction.

Exercise 96. Quiz “Electromagnetism”. Divide into two teams.

Team A – look at the information below.

Team B – look at exercise 100.

Step 1.Each team discuss their questions, choose the correct answer from their point of view, then ask a teacher to check them. For every correct answer they get 10 points, incorrect answer – 0 points.

Step 2. Each team takes turns reading a question and four possible answers. Another team must choose the correct answer. If they are not sure, they can play a '50:50 Joker' and hear the question again with only two answers.

SCORING:

Correct answer: 10 points.

Correct answer with a Joker: 5 points.

Incorrect answer: 0 points.

Team A. Take turnsasking peopleon the other team these questions. Read the four possible answers too.

Questions:

1. The magnetic effects of a bar magnet are

A. evenly distributed throughout a magnet

B. distributed randomly in a magnet.

C. concentrated near the ends.

D. None of the above.

2. If you attach a magnet to a string so that the magnet is free to rotate, you will see that one end of

A. north. C. east.

B. southwest. D. west.

3. The pole of a magnet that points to the south is called the magnet's

A. north pole. C. east pole.

B. south pole. D. west pole.

4. A compass needle is

A. a fixed magnet.

B. a fixed nonmagnetic piece of metal.

C. a magnet that is free to rotate.

D. a nonmagnetic piece of metal that is free to rotate.

5. Whether a material is magnetic depends on the ____ in the material.

A. molecules. C. number or neutrons.

B. atoms. D. number of protons.

6. Why are most materials not magnetic?

A. The electrons stop moving.

B. Only atoms can have magnetic fields.

C. The magnetic fields of the individual atoms cancel each other out.

D. Most atoms don't have magnetic fields

7. A magnet can demagnetize if

A. it is dropped. C. it is struck very hard.

D. it is heated. D. All of the above.

8. Permanent magnets

A. cannot lose their magnetization.

B. are difficult to magnetize.

C. have randomly oriented domains

D. are easy to magnetize.

9. A magnet, usually with an iron core, produced by an electric current is

A. electromagnet. C. temporary magnet.

B. ferromagnet. D. permanent magnet.

10. Magnetic poles are similar to electric charges in that

A. like poles repel and opposite poles attract.

B. the magnetic force is equal to the electric force.

C. the number of magnetic domains responsible for the poles is conserved.

D. the mass of the magnetized particle is conserved.