Humans and electricity

Electricity is a basic part of nature and it is one of our most widely used forms of energy. Humans get electricity, which is a secondary energy source, from the conversion of other sources of energy, like coal, natural gas, oil and nuclear power. The original natural sources of electricity are called primary sources.

Many cities and towns were built alongside waterfalls (a primary source of mechanical energy) that turned water wheels to perform work. And before electricity generation began slightly over 100 years ago, houses were lit with kerosene lamps, food was cooled in iceboxes, and rooms were warmed by wood-burning or coal-burning stoves. Beginning with Benjamin Franklin's experiment with a kite one stormy night in Philadelphia, the principles of electricity gradually became understood. In the mid-1800s, everyone's life changed with the invention of the electric light bulb. Prior to 1879, electricity had been used in arc lights for outdoor lighting. The lightbulb's invention used electricity to bring indoor lighting to our homes.

Generating electricity

An electric generator (Long ago, a machine that generated electricity was named "dynamo" today's preferred term is "generator") is a device for converting mechanical energy into electrical energy. The process is based on the relationship between magnetism and electricity. When a wire or any other electrically conductive material moves across a magnetic field, an electric current occurs in the wire.

The large generators used by the electric utility industry have a stationary conductor. A magnet attached to the end of a rotating shaft is positioned inside a stationary conducting ring that is wrapped with a long, continuous piece of wire. When the magnet rotates, it induces a small electric current in each section of wire as it passes. Each section of wire constitutes a small, separate electric conductor. All the small currents of individual sections add up to one current of considerable size. This current is what is used for electric power.

An electric utility power station uses either a turbine, engine, water wheel, or other similar machine to drive an electric generator or device that converts mechanical or chemical energy to electricity. Steam turbines, internal-combustion engines, gas combustion turbines, water turbines, and wind turbines are the most common methods to generate electricity.

Vocabulary:

magnetism and electricity – магнетизм и электричество arc lights – блики света

stationary conductor – стационарный проводник internal-combustion engines – двигатель внутреннего сгорания

Speed of light

Light moves through the universe at the fastest speed astronomers can measure. In fact, the speed of light is a cosmic speed limit, and nothing is known to move faster.

21

How fast does light move? This limit can be measured and it also helps define our understanding of the universe's size and age.

What Is Light?

Light travels fast, at a velocity of 299, 792, 458 meters per second. How can it do this? To understand that, it's helpful to know what light actually is and that's largely a 20th-century discovery.

The nature of light was a great mystery for centuries. Scientists had trouble grasping the concept of its wave and particle nature. If it was a wave what did it propagate through? Why did it appear to travel at the same speed in all directions? And, what can the speed of light tell us about the cosmos? It wasn't until Albert Einstein described this theory of special relativity in 1905 it all came into focus. Einstein argued that space and time were relative and that the speed of light was the constant that connected the two.

What Is the Speed of Light?

It is often stated that the speed of light is constant and that nothing can travel faster than the speed of light. This isn't entirely accurate. The value of 299,792,458 meters per second (186,282 miles per second) is the speed of light in a vacuum. However, light actually slows down as it passes through different media. For instance, when it moves through glass, it slows down to about two-thirds of its speed in a va-

cuum. Even in air, which is nearly a vacuum, light slows down slightly. As it moves through space, it encounters clouds of gas and dust, as well as gravitational fields, and those can change the speed a tiny bit. The clouds of gas and dust also absorb some of the light as it passes through.

This phenomenon has to do with the nature of light, which is an electromagnetic wave. As it propagates through a material its electric and magnetic fields "disturb" the charged particles that it comes in contact with. These disturbances then cause the particles to radiate light at the same frequency, but with a phase shift. The sum of all these waves produced by the "disturbances" will lead to an electromagnetic wave with the same frequency as the original light, but with a shorter wavelength and, hence a slower speed.

Interesting, as fast as light moves, its path can be bent as it passes by regions in space with intense gravitational fields. This is fairly easily seen in galaxy clusters, which contain a lot of matter (including dark matter), which warps the path of light from more distant objects, such as quasars.

Lightspeed and Gravitational Waves

Current theories of physics predict that gravitational waves also travel at the speed of light, but this is still being confirmed as scientists study the phenomenon of gravitational waves from colliding black holes and neutron stars. Otherwise, there are no other objects that travel that fast. Theoretically, they can get close to the speed of light, but not faster.

One exception to this may be space-time itself. It appears that distant galaxies are moving away from us faster than the speed of light. This is a "problem" that scientists are still trying to understand. However, one interesting consequence of this is that a travel system based on the idea of a warp drive. In such a technology, a spacecraft is at rest relative to space and it's actually space that moves, like a surfer riding a wave

22