Lesson 2

Oersted and Faraday.

Starter: Electricity and magnetism are closely linked. In what way?

Input: Oersted’s Experiment

In the winter of 1819-20 Christian Oersted was doing experiments to find links between electricity, magnetism, light and heat. One of these experiments was very important, as it was the first step towards the invention of the generator or dynamo.

Oersted’s apparatus was very simple. He took a piece of wire and bent it to make a kind of bridge. Leads to the terminals of an electric battery could connect the ends of the wire. The only other piece of equipment was a pivoted magnet, like a compass needle.

It had long been known that magnets have two poles - north and south. Unlike poles attract and like poles repel. Oersted also knew that there was a relationship between electricity and magnetism and he showed this by placing the magnetic needle below the wire, then connecting the wire to the battery. The needle was deflecting by the current in the wire. The wire was acting like another magnet and influencing the magnetic needle below it. What made the experiment so important was the next stage: when he placed the needle above the wire the needle was again deflected, but this time in the opposite direction.

Oersted concluded that there must be some sort of circular power or force around the wire. This force made the magnet move in opposite directions depending on its position relative to the electrically charged wire.

Gathering Information.

Step 1.

Draw a diagram to illustrate the second part of the experiment. Label the diagram with these words; wire bridge; battery; terminals; pivoted needle direction of deflection; connecting leads.

Step 2.

Are the following statements true or false? Correct any that is wrong.

a) Oersted was trying to show that electricity and magnetism were not related.

b) For this experiment he used a kind of compass needle, a wire bridge and an electric generator.

c) He first placed the magnetic needle underneath the wire, then connected the wire to the battery.

d) The needle under the wire was pushed first one way, then the other.

e) In the second part of the experiment he put the needle above the wire.

f) The needle above the wire was not deflected at all.

g) Oersted thought the wire was surrounded by a magnetic field.

Step 3.

Find words and expressions in the Input with similar meanings to the followings: free to turn, pushed away, beneath, connection, carrying an electric current, apparatus, a form of, put.

Step 4.

The bottom diagram represents the magnet in the top diagram broken into pieces. None of the pieces has been moved. Draw the bottom diagram and mark in the poles.

N S

Step 5.

Why is Oersted’s experiment described as the first step towards the invention of the generator or dynamo?

Steps 6.

Here are the instructions for a simple experiment with a magnet. You have just done this experiment.

Now write the report. Start like this: The aim of the experiment was to show why the like poles of a magnet repel and the unlike poles attract. We took...Continue.

Why do the like poles repel?

Take a sheet of cardboard, a magnet, a handful of iron filings and a compass. Put the magnet under the sheet of cardboard and scatter the iron filings on the top of the card.

Tap the edge of the card lightly. The iron filings will make a pattern. They will form a series of loops between the two poles of the magnet. Place the compass on one side of the magnet and then on the other. You will see that the compass needle follows the loops. This shows that there are lines of force, which leave the magnet at one pole and enter it again at the other pole.

Step 7.

Reporting writing

a) Look at your answers to Step 2. The true statements and your corrected statements make a summary of the Oersted’s experiment.

The list below gives the various stages of the summary, but they are in the wrong order.

Match the stages with the seven sentences of your summary.

Observation Apparatus

Procedure Conclusion

Observation Procedure

Purpose of the experiments:

b) Look carefully at the stages of the summary and answer these questions:

1. Could the structure be applied to any experiment?

2. Which parts could be left out, depending on the experiments?

3. Could the order be changed?

c) Name the stages in the magnetism experiment in Step 6.

Step 8.

Read this description of one of Faraday’s experiments and make a summary of it. Use the structure you practiced in Step 7

Oersted’s experiments did not have any immediate practical application. All he had done, in effect, was to show that a wire carrying an electrical current acts like a magnet. The thing that most interested scientists was the question of whether the opposite was true, could magnets be used to induce an

electric current?

Michael Faraday an English scientist carried out a series of experiments to find the answer to this question. His work led to the development of the electric generator and so made it possible to produce electricity on a large scale.

In one of his experiments, Faraday connected a coil to a simple ammeter. Then he took a bar magnet and moved it quickly towards the coil. The ammeter showed a momentary current. When the magnet was moved quickly away from the coil, the ammeter again registered a current but in the opposite direction.

Faraday’s experiments were only the first steps, but he had shown quite clearly that magnets could be used to produce an electric current. The next step was to show that a momentary movement should induce a continuous current. This is the principle on which all electric generators (and motors) are based