In this chapter, we will examine electromagnetism and the effects of electromagnetic induction, one of the greatest discoveries of physics of all times that changed the world forever.
9.2 The Theory
The effects of magnets over certain materials and their interference in compasses were well known for centuries.
The discovery that magnets have poles and that identical poles repel and opposite poles attract each other came later.
Electricity and magnetism were seen as separate entities, with no relation to each other and no practical usage in daily life.
9.3 Hans Christian Ørsted
In 1890, Hans Christian Ørsted, a Danish physicist, discovered that an electric current was able to produce a magnetic field.
The proof was simple: a battery connected to a wire suspended over compasses and a switch initially open.
Without current, the compasses all point to the Earth’s magnetic north, as expected, as illustrated in Figure 9.1.
As soon as the switch is closed, current flows across the wire and gives rise to a magnetic field. This magnetic field interferes with the compasses that move to follow the field, as illustrated in Figure 9.2.
Placing the compasses over the wire would make their needles point to the opposite direction. We will know why in the following paragraphs.
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