James Clerk Maxwell
Who was James Clerk Maxwell?
James Clerk Maxwell was a 19th century Scottish physicist. Maxwell is chiefly associated with the paradigm shift in physics that allowed us to understand the phenomena of light, electricity and magnetism. He was a Professor of Natural Philosophy (what we call physics today) in Edinburgh and at King’s College London. Maxwell demonstrated that magnetism, electricity and light are manifestations of the same fundamental law. Maxwell’s equations paved the way for current technologies in radio, television, mobile phones, the Internet and GPS.
What did we know about physics at the middle of the nineteenth century?
Physics is the scientific study of matter, energy, motion and the fundamental forces of nature. Modern physics progressed in three great leaps, associated with three great minds. The first of these was the English scientist Isaac Newton (1643-1727). Newton’s laws are also called the laws of classical mechanics, because they give a mechanical explanation for actions, forces and energy. The first of Newton’s laws states that an object will remain in a state of inertia unless a force acts upon it. This includes moving objects, which, minus any resistance, will continue to move in the same direction at the same speed indefinitely. The second of Newton’s laws is F = m.a or Force = Mass x Acceleration. The third of Newton’s laws states that for every force, there is an equal and opposite reaction force.
Newton is also known for the law of universal gravitation, famously conceived when an apple fell on his head, which states that every particle in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centres.
These laws provide a tidy explanation for the physical universe - or so it was thought! Scientists after Newton wanted to understand light, electricity and magnetism. They thought these observable phenomena must obey Newton’s laws, since everything else in the world obeyed these laws. However, they had trouble making the evidence fit their beliefs!
What were Maxwell’s field equations? What is the electromagnetic field?
Maxwell is chiefly associated with the paradigm shift that allowed us to understand the phenomena of light, electricity and magnetism. Maxwell comprehensively covered this area of physics, producing four field equations related to electric fields, magnetic fields and electromagnetic induction. For years, his theory was considered unintelligible. However, the key to understanding it is to give up thinking in terms of mechanical models.
Scientists were trying to force the observable world to fit a paradigm that fundamentally didn’t describe reality. Lightwaves are not generated by forces and motion, but by disturbances in a different medium, called the electromagnetic field. Though they have energy, it is not kinetic.
Maxwell proposed that light is an undulation in the same medium through which electric and magnetic phenomena occur, and that they are different manifestations of the same phenomena.
“Another theory of electricity which I prefer denies action at a distance and attributes electric action to tensions and pressures in an all-pervading medium, these stresses being the same in kind with those familiar to engineers, and the medium being identical with that in which light is supposed to be propagated.”
How did Einstein change our understanding of physics?
The third leap in modern physics is associated with Albert Einstein, some forty to fifty years after the work of Maxwell. Einstein in his annus mirabilis (miracle year) of 1905, published four fundamental papers in Annalen der Physik (Annals of Physics). In the first, he explained the photoelectric effect, in the second, he proved the existence of atoms, in the third he formulated the theory of special relativity and in the fourth, he derived the law of mass and energy equivalence. This last theory is the basis for nuclear energy. General relativity is the geometric theory of gravitation published by Einstein in 1915. This refinement of Newton’s law of universal gravitation stated that objects with mass warp the fabric of spacetime, resulting in some of the phenomena we observe with light around objects with massive gravity.
What do we know today about how matter, energy and motion apply to electricity, light and magnetism?
We now have a better idea of how matter, energy and motion apply to electricity, light and magnetism.
Light is now considered to behave as both a wave and a particle. As a particle, it is called a photon. A photon is a very small packet of energy. However, light is transmitted in waves; different colours across the spectrum from ultraviolet light to infrared light have different wavelengths. They all travel at the same speed, the speed of light, the fastest speed in the universe.
Magnetic materials have a special quality. The electrons in an atom can be influenced to concentrate at one end, creating a magnetic pole. The magnetic effect or the magnetic force can be converted into kinetic energy, giving us a wide range of practical uses and applications, such as road vehicles.
The fundamental law of electricity is Ohm’s law, Voltage = Current x Resistance. Voltage is a charge differential. Electrified material can be positively or negatively charged. Nature will try to balance the charge differential through an electric current between the opposite charges. Materials that can carry current are mostly transition metals, because these elements have untethered electrons (negative charge carriers). Graphite exhibits the same property due to the structure of its carbon atoms.
Maxwell gave us electromagnetic induction
Both the electric effect and the magnetic effect are based on the energy of electrons. These subatomic particles became the subject of study in the 20th century, with the advent of subatomic physics, a field that has grown steadily since Ernest Rutherford discovered the atomic nucleus in 1911.
Because they both are phenomena in the electromagnetic field, they can influence each other. This was Maxwell’s big contribution to physics. Before we had identified what an atom was, he surmised that electricity and magnetism were manifestations of the same phenomena. He found that an electric current will generate a magnetic field, and a changing magnetic field can induce an electric current.
These brilliant observations were crucial for economic and societal development, because the principles are used in some of our most common innovations. A hydropower dam, for instance, uses the force of water to turn a turbine. The kinetic energy of the turbine turns an electromagnet, which generates an electric current. In this way, hydropower can be used to generate clean electricity. An electric motor uses a battery to start an electric current which generates a changing magnetic field. This rotates an electromagnet connected to a shaft. This is all thanks to the discovery of the electromagnetic field. Our world does obey the laws of classical mechanics, but Newton’s laws are not the only laws that govern matter, energy and motion.