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  • Visible light and the solar system
    • Light is refracted and reflected at surfaces and boundaries between different materials. Refracting telescopes use an objective lens to form a real image, which is then magnified. Reflecting telescopes use a concave mirror, which gives a clearer image and allows larger telescopes to be made.
    • The model of the universe changed from a geocentric to a heliocentric model. Observations of the Universe in the past used light, but nowadays many different types of wave are used to gain more evidence.
    • Waves (transverse or longitudinal) transmit energy but not matter. They are described in terms of wavelength, frequency and amplitude.
  • The electromagnetic spectrum
    • The EM spectrum is a family of waves that all travel at the same speed in a vacuum. They are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. A simple way of remembering this is: Reindeer Meat Is Very Unusual X-mas Gift.
    • Ionising alpha, beta and gamma radiation comes from the nucleus of radioactive elements. The higher the  frequency of the EM waves, the higher the ionising power.
  • Waves and the Universe
    • The Solar System is our group of planets, moons, asteroids and comets that orbit the sun. Scientists study the Universe with all the parts of the EM spectrum.
    • Nuclear reactions take place within all stars, which give out vast amounts of energy in the form of EM waves.
  • Waves and the Earth
    • The human hearing range is approximately 20 Hz to 20000 Hz. Frequencies lower than 20 Hz are called infrasound. Frequencies higher than 20000 Hz are called ultrasound.
  • Generation and transmission of energy
    • Power is the rate at which energy is used. Power (W) = current (A) X potential difference (V).
    • Fossil fuels are non-renewable resources. Burning them contributes to the greenhouse effect. Renewable energy resources include: wind, waves, tidal, hydroelectric and solar.
    • EM induction occurs when there is relative motion between a wire and a magnetic field. An electric current is generated. Electricity generated in power stations is alternating energy (a.c). Electricity from a battery is direct current (d.c). Transformers are used to change the voltage of a.c electricity.
  • Energy and the future
    • Energy can't be created or destroyed - only converted from one form to another, as depicted in Sankey diagrams. In all energy transfers, some energy is wasted as heat.
    • All objects at temperatures above absolute zero emit infrared radiation.

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