Page 313 - General Knowledge

GENERAL KNOWLEDGE 2019

 The temperature that a metal becomes superconducting is called its critical temperature.
They are used to:
 Conduct electricity without losing power (increasing efficiency)
 Create magnetic storage systems that can be used to store electricity.
 Reduce the heat in electronics
 Levitate maglev trains
The Greenhouse Effect
 The trapping of heat is called the greenhouse effect.
 The gases (carbon dioxide, methane) in the atmosphere trap some of this heat. At night, the
heat escapes.
 Carbon dioxide traps more heat than any other gas. Too much of this can cause a rise in
temperatures and sea levels.
 The increase in temperature in a glass or plastic wall structure (greenhouse) caused by
radiant energy from the Sun allows heat to enter, but not leave.

 A similar effect may cause the average temperature of the Earth‘s atmosphere to rise.
 Energy from the Sun is able to pass through the atmosphere to the Earth.
 However, the heat energy radiated back by the Earth has a greater wavelength, and is
absorbed by atmospheric carbon dioxide and water vapour, thus warming the atmosphere.

Energy Sources
 Energy is a limited resource. Around 80% of the world‘s energy comes from the burning of
fossil fuels which are formed by the remains of plants and animals millions of years ago.
 The majority of the generation of electricity is caused by the burning of coal, natural gas
and oil.
 Australia has a large supply of coal, which is burnt and the steam that is produced turns a
generator. It isn‘t efficient, with only 35% of the energy produced is used.
 There are other types of energy sources that can be used to generate electricity.
 Nuclear energy is one, however, the radioactive waste and the safety of a reactor has
damaged its credibility.
 Renewable energy is energy that can be replaced all the time.
 They are clean and safe. However, they can be expensive and can cause damage to plants
and animals.
 These include wind power, wave power, hydro-electric power, tidal power, geothermal
power, solar power and biomass power.

10. ATOMIC PHYSICS AND NUCLEAR PHYSICS
Positive rays or Canal rays
 Positive rays are sometimes known as the canal rays. If the cathode of a discharge tube has
holes in it and the pressure of the gas is around 1 mm of mercury than luminous glow come
out from each hole on the backside of the cathode.
 This shows that something is coming out of the holes. These are called canal rays or
positive rays.

Thomson atom model
 J.J. Thomson tried to explain the arrangement of positive charge and the electrons inside
the atom. According to him, an atom is a sphere of positive charge having a radius of the
-10
order of 10 m.

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