Physics Lesson 16.7.1 - What did Faraday Observe during His Experiments?

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Welcome to our Physics lesson on What did Faraday Observe during His Experiments?, this is the first lesson of our suite of physics lessons covering the topic of Faraday's Law of Induction, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

What did Faraday Observe during His Experiments?

In tutorial 16.2 "Magnetic Field Produced by Electric Currents", we stated that Faraday did a famous experiment in which he discovered that a moving magnet generates electricity in a conducting wire if moved properly. We can observe better this property by making two experiments as follows.

First experiment. Let's consider a circular loop connected to a very sensitive ammeter as shown in the figure.

Physics Tutorials: This image provides visual information for the physics tutorial Faraday's Law of Induction

If we move the magnet towards the loop (direction 1), the ammeter arrow moves and indicates a non-zero current. The same thing occurs when the magnet moves in the opposite direction as well (direction 2). The only case when the ammeter shows zero current is when the magnet is changing direction. It is known than when an object is changing direction, stops for a while (for example, when we throw an object upwards, the velocity at the maximum position is zero).

This experiment shows that:

Only a moving magnet is able to produce electric current in the loop; a stationary magnet does not produce any current.
Faster the motion of magnet, greater the current produced in the loop.
The direction of current changes when the direction of magnet's motion changes. For example, if we move the magnet towards the loop and the current produced is let's say clockwise, the direction of current in the loop will be anticlockwise if we move the same magnet away from the loop.

As we have stated in the tutorial 16.2, the current produced through this method is called induced current, as it is not obtained through direct contact but through induction. The work done to move the charges throughout the loop by means of this method is called induced emf (induced electromotive force).

Second experiment. For this experiment, we need two circular loops to be placed near each other, where one of them is connected to an electric circuit and the other to an ammeter as shown in the figure.

When the switch S turns on, the ammeter shows some current flowing through the left circular loop despite the loops are not touching each other. However, after a while the ammeter shows no current despite the switch is ON. When we turn the switch OFF, the current flows again through the left loop as the ammeter shows some current again.

This experiment is a demonstration that an induced current (and an induced emf) is produced in the loop connected to the ammeter (on the left side) due to the magnetic effect of current flowing in the loop on the right connected to the battery. Since this current is not produced through direct contact, it is an induced current. This current is not constant; it changes value and direction continuously every time we change the position of switch.

The two above experiments are demonstrations that a current is produced in the loop only if there is a change of something in proximity of loop. The reason why this change occurs, accompanied with the relevant theoretical explanation for which we will discuss in the next paragraph, was provided by Michael Faraday. That's why it is called the Faraday's Law of Induction.

You have reached the end of Physics lesson 16.7.1 What did Faraday Observe during His Experiments?. There are 4 lessons in this physics tutorial covering Faraday's Law of Induction, you can access all the lessons from this tutorial below.

More Faraday's Law of Induction Lessons and Learning Resources

Magnetism Learning Material
Tutorial ID	Physics Tutorial Title	Revision Notes	Revision Questions
16.7	Faraday's Law of Induction
Lesson ID	Physics Lesson Title	Lesson	Video Lesson
16.7.1	What did Faraday Observe during His Experiments?
16.7.2	Faraday's Law of Induction
16.7.3	Induced Electromotive Force as Motional Emf
16.7.4	Motional Emf and Electrical Energy

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