Subject: How does a compass work?

Supplementary material for use in lessons in the group of natural sciences (nature, biology, chemistry, geography, physics), additional classes, science clubs. It can serve as a resource for expanding knowledge, preparing students for science competitions.

Author: Zyta Sendecka

Target group

Students of an elementary school (physics).

Core curriculum

8th grade physics

VII. Magnetism. Student:

2) describes the behaviour of a magnetic needle in the presence of a magnet and the principles of the compass; uses the concept of Earth's magnetic poles;

4) describes the behaviour of a magnetic needle in the vicinity of a straight current conductor.

Lesson objective

Students describe the structure, principle and applications of a compass.

The criteria for success

• you will describe the principle of a compass;

• you will name the Earth’s magnetic poles;

• you will build a compass and use it to point north and south;

• you will orientate a map using a compass;

• you will indicate the items that affect the compass.

Key competences

• communication in the mother tongue;

• communication in foreign languages;

• mathematical competence and basis competences in science and technology; 

• digital competence;

• learning to learn;

• social and civic competences.

Methods/forms of work

Talk, working with the text, workshop method, traffic lights method.

Individual activity and activity in pairs.

Teaching aids

• abstract;

• interactive whiteboard or traditional blackboard;

• tablets/computers;

• compasses;

• maps;

• magnets;

• post‑it notes;

• sewing needle;

• cork or piece of polystyrene;

• bowl;

• water;

• table tents;

• smoothing iron.

Before classes

Students prepare a set of items that they will bring to the lesson. It consist of: sewing needle, cork or piece of polystyrene, bowl.

Lesson plan overview

Introduction

1. The teacher asks the students two questions:
   ● How many and what poles does a magnet have?
   ● What happens to magnets when unlike poles are brought close to each other?

2. The teacher specifies the subject, the lesson objectives in a language the student understands, and the criteria for success.

Realization

1. The teacher distributes compasses to the students. The teacher asks the students to name these items and explain what they are used for. Volunteer students give their answers.

2. The students read the fragment entitled „What is a compass?” and watch an interactive illustration showing the compass construction, and then evaluate the correctness of previous colleagues' responses.

3. The teacher explains the principle of the compass and discusses the issue of the Earth's magnetic field and magnetic poles.

4. Students do interactive exercise no. 1.

5. The teacher distributes to the students post‑it notes with a letter “N” or “S”. The students are to point, using their own compass, the direction written on the post‑it note and place the post‑it note on the wall pointed by the compass. After completing this task, the teacher discusses possible mistakes.

6. The instructor, using a compass, demonstrates how to orientate the map in relation to the directions of the world. He then distributes the maps and compasses to the mentees. Students, according to the teacher's instructions, orientate the received map, then pair up and check each other for the correctness of the task.

7. The teacher asks the students to answer the question: “Is it possible to interfere with the operation of the compass?”. The students give their answers using table tents: red card means “no”, green one – “yes”.

8. The teacher offers students an experiment to examine the impact of metal objects on the operation of the compass („Experiment 1”).

9. The teacher once again asks the students to answer the question: “Is it possible to interfere with the operation of the compass?”. As before, the students give their answers using a table tent.

Summary

1. Students do interactive exercise no. 2.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

How does a compass work?

Compass is a simple device used for navigation, i.e. to establish a route to a given destination and to find a way. The most important element of the compass is the rotating magnetic needle. It is used to determine the cardinal directions. Since the compass needle has the characteristics of a magnet, this also means that it has two poles: one north and one south. The needle rotates so that one end points to the north and the other to the south. How does this happen? Does the needle point exactly to these cardinal directions? We need to find out the principle of a compass to answer these questions.

Let’s think why and how does a compass work. The compass needle is made of a material that has magnetic properties. Is there a magnetic field around us we are not aware of?

Deep inside our planet there is a core. This core produces the Earth’s magnetic field. The lines of this field are aligned north‑south more or less. The compass needle reacts to this field. It aligns itself along the lines of the Earth’s magnetic field.

Compass – when placed near metallic objects – can stop working properly. For this reason, classic compasses are completely useless on steel ships, for example – steel contains iron. Another case where the compass stops working is when it is close to electrical devices or magnets.

All compasses have a movable magnetic needle. A dial with marked cardinal directions is usually inserted into the compass housing. However, we can build the simplest compass on our own. All we need is a sewing needle, a strong magnet, a cork or polystyrene and a dish with water.

When we want to use the map in the field, we need to orientate it in relation to the cardinal directions. This means that geographical directions on the map must show the real directions. So we have to position ourselves in such a way that the northern direction on the map corresponds to the north in the field.

Usually the northern direction on the map is at the upper edge – unless the signs indicate otherwise. You can make sure this is the case by using the compass. Modern compasses have needles suspended in the liquid (e.g. alcohol), which prevents their vibrations. It is important to remember that we should not use compasses near objects that interfere with the magnetic needle – i.e. near large iron and steel objects or working electrical devices.

• Compass is a device that shows the cardinal directions.

• The basic element of a compass is a movable magnetic needle, which aligns itself along the Earth's magnetic field lines.

• Electrical devices, magnets and iron containing objects in the vicinity may interfere with the operation of the compass.