Electric power

• In a power station, electricity is created by a generator. In a generator, coils of wire are typically driven around between electromagnets to induce an electricity current in the coils.

• The magnets in the generator in most large power stations are turned by turbines, which have blades like fans. In some power stations, the turbine blades are turned either by steam heated by burning fossil fuels such as coal or with nuclear fuel, or by the flow of natural gas. In others, they are turned by moving wáter (hydro-electric power) or wind.

• Simple dynamos generate a direct current (DC) -an electric current that always flows in the same direction.

• Power station generators are alternators. They give an alternating current (AC) -a current that continually swaps direction.

• Electricity from power stations is distributed around a country in a network of cables known as the grid.

• Power station generators generate upwards of 25,000 volts. This is too much to be used safely in homes, but too Little to transmit over long distances.

• To transmit electricity over long distances, the voltaje is bossted to 400,000 volts by transformers. It can then be transmitted through high-voltaje cables. Near its destination, voltage is reduced to a level safe for use in homes.

 

BIBLIOGRAPHY (ISO 690)

 

GALLAGHER, Belinda. Science. First edition. UK: Miles Kelly, 2014. 384 p. ISBN: 9-781848-103023

Jacob Sierra Díaz

Musical Sound

Like all sound, a musical note is created by a vibration of air. Musicians control the frequency and volume of these vibrations to play tunes.

The pitch (level) of a musical note depends upon the frequency of the vibrations.

Sound frequency is measured in Hertz (Hz), which refers to the number of cycles or waves per second.

Human ears can hear sounds within a frequency range of 20 - 20,000 Hz

Middle C on a piano measures 262 Hz. A piano has a frequency range from 27.5 - 4186 Hz

The highest singing voice can reach the E above a piano top note (4350 Hz), while the lowest is 20.6 Hz

Few sounds have only one pitch. Most have a fundamental (low) pitch and higher overtones.

The frecuency at which an object naturally vibrates is called its resonant frecuency. A musical note can shatter glass if its frequency coincides with the resonant frequency of the glass.

 

 

 

 

BIBLIOGRAPHY (ISO 690)

 

GALLAGHER, Belinda. Science. First edition. UK: Miles Kelly, 2014. 384 p. ISBN: 9-781848-103023

 

 

Jacob Sierra Díaz