075

The Royal Institution of Great Britain, London, England

51° 30′ 35.28″ N, 0° 8′ 33″ W

Furthering the Public Understanding of Science

When it comes to the public understanding of science, one ancient institution stands out—the Royal Institution of Great Britain. It was founded in 1799 with a specific goal: “diffusing the knowledge, and facilitating the general introduction, of useful mechanical inventions and improvements; and for teaching, by courses of philosophical lectures and experiments, the application of science to the common purposes of life.” To this day, the Royal Institution hosts public lectures including the popular Christmas Lectures (specifically aimed at children), which were started in 1825 by Michael Faraday and only took a break for the Second World War.

Since its establishment, many great scientists have worked and even lived at the Royal Institution. Faraday lived for many years in a small apartment in the Institution, where he worked (mainly in the basement) on chemistry and electricity. A self-taught man and a highly religious Christian, he discovered electromagnetic induction (see sidebar), worked out the laws of electrolysis (which show the relationship between the amount of electricity passing through a solution and the mass of chemicals produced), and demonstrated that magnetism could bend light. He discovered benzene, and coined the terms anode, cathode, electrode, and ion.

Faraday was also the first to make dynamos and electric motors, and invented the Faraday cage (see page 196).

Faraday initially became interested in science in part because he was able to attend public lectures at the Royal Institution given by Sir Humphrey Davy, who had helped get the Royal Institution going. Davy is best known for the Davy Lamp (page 265), but also discovered a list of elements including sodium, potassium, calcium, magnesium, barium, and boron. In total, the Royal Institution has seen 10 elements discovered on its premises.

The Australian physicist Sir William Lawrence Bragg (who worked on X-ray diffraction and won the Nobel Prize) was Fullerian Professor of Chemistry at the Royal Institution (as was Faraday).

The history and science behind the Royal Institution is explored in a completely renovated museum (formerly known as the Faraday Museum) split over three floors. In the basement where Faraday worked is an area entirely dedicated to experimentation. There’s a reproduction of Faraday’s own laboratory made with his actual equipment, and clear and varied displays of equipment used from the earliest days of the Royal Institution to the present.

The basement exhibition covers topics as varied as electrolysis and electromagnetism, nanotechnology and glass making, the creation of X-rays and the experiment that explained why the sky is blue.

The other floors are devoted to the people associated with the Royal Institution, and the institution’s communication and education work.

Practical Information

Visiting information for the Royal Institution is available at http://www.rigb.org/. There’s a small café called Time and Space inside the building, if you find yourself in need of a science-filled place for lunch; it too is filled with historical objects.

Electromagnetic Induction

Michael Faraday was not the first person to discover electromagnetism, but he did bring together the work done by others to create the theory of electromagnetism. And Faraday discovered electromagnetic induction, which is fundamental to the operation of motors, dynamos, generators, and transformers.

Electricity and magnetism are inextricably linked—electricity passing through a wire generates a magnetic field around the wire, and a wire moving through a magnetic field has electricity created in it. In fact, wherever there’s a changing magnetic field there’s an electric field, and wherever there’s a changing electric field there’s a magnetic field.

Faraday discovered that if he wrapped two coils of wire around an iron ring, then a current passed through one coil would create a current in the other. His experiment is on display at the Royal Institution and is the first example of a transformer. It shows electromagnetic induction—a changing current in one coil creates a magnetic field, and the changing magnetic field then creates a changing current in the other coil.

He also showed that moving a coil of wire over a permanent magnet caused a current to be created in the wire—the current is said to be induced in the wire. And since a coil of wire creates a magnetic field when electricity passes through it, it’s possible to create movement because the coil will be repelled or attracted to a permanent magnet. With these experiments, Faraday was able to create practical dynamos and motors.

He is also responsible for Faraday’s Law of Induction (Equation 75-1). This states that the electromotive force, E, induced in a circuit by a changing magnetic field is equal to the rate at which the flux of the magnetic field, Φ, changes.

Equation 75-1. Faraday’s Law of Induction

The electromotive force expresses the amount of energy that a device (such as a battery) will add to electrons passing through it. Strictly speaking, this is the energy added per unit of charge passing through the device and is measured in volts (in fact, Volta—see Chapter 26—was the first person to speak about the electromotive force). When talking about a battery or a generator, its electromotive force is more commonly called its voltage.

The flux of a magnetic field is the quantity of magnetism in a magnetic field over some area. When a magnetic field is inducing a current in a wire, the flux is based on the strength of the magnetic field and the area of the wire the magnetic field passes through. The flux of a magnetic field over some area is the strength of the field times the area.

Thus, increasing the strength of the magnetic field, or the amount of wire the field passes through (which is why coils of wire are typically used) increases the amount of electromotive force induced.

And Faraday’s Law of Induction explains how to construct transformers. A simple transformer is exactly what Faraday originally built: a pair of coils of wire (of the same gauge) wrapped around an iron ring. When a changing electric current is passed through one coil, a changing electric current of a different voltage is created in the other coil (see Figure 75-1). The ratio of the two voltages is explained by Faraday’s Law.

Figure 75-1. A transformer

The coils of wire in a transformer are referred to as the primary winding (where the voltage to be transformed is applied) and the secondary winding (where the transformed voltage is present). When a voltage of VP is applied across the primary winding, it generates a magnetic field with a flux that follows Faraday’s Law. Because the coil is wound around the iron many times, the effective area is proportional to the number of turns, NP , meaning that the resulting magnetic flux depends also on the number of turns (Equation 75-2).

Equation 75-2. Faraday’s Law applied to the primary winding

The induced magnetic field passes through the secondary winding, inducing a current with a voltage, VS, that is once again proportional to the number of turns, NS (Equation 75-3) in the secondary.

Equation 75-3. Faraday’s Law applied to the secondary winding

Since the magnetic flux is the same in both cases (assuming an ideal transformer and no loss of flux), it can be eliminated to show that the ratio of voltages in a transformer is equal to the ratio of turns in the two coils (see Equation 75-4). To make a simple transformer capable of converting European 220V to U.S. 110V, a ratio of 2:1 (primary:secondary) is needed for the two coils. A cell phone charger that takes 110V and converts it to 5V would needed a transformer with a winding ratio of 22:1.

Equation 75-4. Voltage ratio in a transformer