Jan 2021

The Principles and Laws of Electromagnetic Induction

January 12, 2021

It is hard to imagine a world without electricity. In our modern society, electricity has become the basis of our comfort, providing us with light, cooling us down, offering entertainment, and so much more. Did you know that electromagnetic induction is used to power many electrical devices? It is possible to use almost any source of mechanical energy, such as flowing water and wind, to generate electric current, as long as it can be attached to an electrical generator.

The law of electromagnetic induction was discovered by Michael Faraday. It is used in designing electric generators and transformers today. Electromagnetic induction is the production of voltage when an electrical conductor cuts through stationary magnetic field lines or a changing magnetic field. The voltage produced is called an induced electromotive force (induced e.m.f.). Read on to learn more about the principles of electromagnetic induction!

Principles of electromagnetic induction
The phenomenon of electromagnetic induction demonstrates that when a conductor, such as a wire, passes through a magnetic field and cuts through the field lines, it induces a current in the wire.

For example, connect the two ends of a coil to a galvanometer (a current measuring device) and place a magnet close to it. The reading on the galvanometer when the magnet is stationary would be zero. You will observe that the galvanometer will point towards the right when the north pole of the magnet is moved towards the coil. It points back to zero when the motion of the magnet stops. If the magnet is moved away from the coil, the current flows in the opposite direction. Thus, the galvanometer points towards the left.

This experiment illustrates that:

The relative motion between the magnet and the coil is responsible for the production of current in the coil.
The direction the galvanometer points is reversed if the direction of the motion is reversed.

Based on the experiment, we can arrive at two laws of electromagnetic induction.

Faraday’s Law
When there is a change in the magnetic flux linking the metal wire coil, an e.m.f. is induced. Faraday’s Law of induction states that the magnitude of the induced e.m.f. is directly proportional to the rate of change in the magnetic flux. In other words, the faster the change in the magnetic field, the greater the induced e.m.f. will be.

Lenz’s Law
Lenz’s Law states that the direction of the induced e.m.f. and induced current in a closed circuit always opposes the change in the magnetic flux producing it.

Electromagnetic induction in an AC generator
While an electric motor is a device that converts electrical energy into mechanical energy, an electric generator does the opposite. It uses mechanical energy to generate electricity using electromagnetic induction. An AC generator applies Faraday’s Law of electromagnetic induction by spinning a coil in a magnetic field to induce an e.m.f. between the ends of the coil.

The voltage in the wire can be increased by moving the wire faster, using a larger coil, or increasing the strength of the magnetic field. Increasing the number of turns of the coil also creates a larger current in the coil.

Fleming’s right-hand rule can be used to determine the direction of the induced current that flows through the wire. According to this rule, display your thumb, forefinger, and middle finger such that all 3 fingers are perpendicular to each other. Given that your forefinger points in the direction of the magnetic field from north to south, the thumb will point in the direction of motion of the conductor, the middle finger will align to the direction of the induced current.

Cathode-ray oscilloscope
A cathode-ray oscilloscope is an electronic display device used to convert electrical signals to visual signals. They are used in applications such as radio stations to observe the transmission and reception of signals. Properties like voltage, current, frequency, and resistance can be calculated using measurements from a cathode-ray oscilloscope.

The cathode-ray oscilloscope provides accurate time and amplitude measurements of voltage signals over a broad range of frequencies. When a cathode-ray oscilloscope is connected to an AC generator, a wave can be seen on the screen. When the speed of the rotation of the generator is doubled, the number of peaks on the screen and the amplitude of the wave will be doubled.

Now that you have a better understanding of the principles of electromagnetic induction, you can explore more on other interesting physics topics! If you are looking for O level physics tuition to excel to the top of your class, we have the best tutors ready to guide you! Sign up for physics tuition here today!

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