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End of chapter exercises

Describe what is meant by the term magnetic field.

It is a region in space where a magnet or object made of magnetic material will experience a non-contact force. A magnetic field has a north and south pole. The direction of the magnetic field is from the north to the south pole.

Use words and pictures to explain why permanent magnets have a magnetic field around them. Refer to domains in your explanation.

Each electron has a magnetic field associated with it. In a ferromagnetic material, a material that a permanent magnet is made of, there are regions where the electrons' magnetic fields line up to point in the same direction. These regions are called domains and they have a net magnetic field. When a ferromagnetic material is magnetised, forming a permanent magnet, most or all these domains line up to create a net magnetic field over the whole object.

 

 

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What is a magnet?

A magnet is an object that has a net magnetic field caused by its electrons' magnetic fields being lined up. This net magnetic field causes a magnet to have a distinct north and south pole.

What happens to the poles of a magnet if it is cut into pieces?

Each piece will have its own north and south pole. If the north pole of the whole magnet was at its right end, then the smaller piece's north pole will also be at its right end. The same holds for the south pole.

What happens when like magnetic poles are brought close together?

They repel each other.

What happens when unlike magnetic poles are brought close together?

They attract each other.

Draw the shape of the magnetic field around a bar magnet.

Explain how a compass indicates the direction of a magnetic field.

The needle of a compass is magnetised. Therefore, when it is inside a magnetic field it will align itself with the direction of the field. The north pole of the needle will point to the south pole of the magnetic field.

Compare the magnetic field of the Earth to the magnetic field of a bar magnet using words and diagrams.

The Earth has a magnetic north pole and south pole and it is surrounded by a magnetic field. This is the same for a bar magnet, except that the Earth's magnetic north pole corresponds to the south pole of a bar magnet. Similarly, the Earth's magnetic south pole corresponds to the north pole of a bar magnet.

 

 

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Explain the difference between the geographical north pole and the magnetic north pole of the Earth.

The magnetic north pole is actually the south pole of the Earth's magnetic field. The geographical north pole is 11,5° degrees away from the direction of the magnetic north pole. The Earth's rotation axis goes exactly through the geographical north pole. While the geographical north pole doesn't move, the magnetic north pole shifts slightly all the time.

Give examples of phenomena that are affected by Earth's magnetic field.

  • The aurora.
  • Some animals, like bees and pigeons, detect Earth's magnetic field and use it to navigate.

Draw a diagram showing the magnetic field around the Earth.