Our understanding of the universe has changed over time. Different civilisations have created different models to explain what the universe is and how the universe began.
The Greek astronomer Ptolemy used measurements of the sky to create his geocentric model. This had the earth at the centre and all the planets and the sun orbiting around it.
The geocentric model lasted a long time. It wasn’t until the mid 18th century that Nicolaus Copernicus came up with a different model.
His heliocentric theory put the sun at the centre if the universe. It was based on observations with the telescope – work pioneered by the Italian astronomer Galileo Galilei.
Sound waves are longitudinal waves. Their vibrations occur in the same direction as the direction of travel. Sound waves can only travel through a solid, liquid or gas.
When an object or substance vibrates, it produces sound. The bigger the vibrations, the greater the amplitude and the louder the sound.
The Big Bang
Scientists have gathered a lot of evidence and information about the universe. They have used their observations to develop a theory called the Big Bang. The theory states that about 13,700 million years ago all the matter in the universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly in a hot explosion, and it is still expanding today.
The Steady State
The Steady State Theory suggests that as the universe expands new matter is created, so that the overall appearance of the universe never changes.
A transformer is an electrical device that changes the voltage of an AC supply. A transformer changes a high-voltage supply into a low-voltage one, or vice versa.
A transformer that increases the voltage is called a step-up transformer
A transformer that decreases the voltage is called a step-down transformer
Step-down transformers are used in mains adapters and rechargers for mobile phones and CD players.
The National Grid
When a current flows through a wire, some energy is lost as heat. The higher the current, the more heat is lost. The National Grid transmits electricity at a low current to reduce these losses. This requires a high voltage.