Electromagnetic (EM) Spectrum List the electromagnetic radiations in order of the energy delivered by each photon
Earth is surrounded by an atmosphere which allows light radiated from the Sun to pass through
Sun = Source Person = Detector UV is absorbed, reflected and transmitted through the atmosphere
Photons A beam of EM radiation delivers energy in ‘packets’ called photons Energy deposited by a beam of EM radiation depends on both the: – Number of photons arriving – Energy that each photon delivers
Intensity Intensity of EM radiation is the energy arriving at a surface each second Intensity decreases with distance and be able to explain why
Ionising Radiation Ionising radiation is able to break molecules into bits (called ions), which can then take part in other chemical reactions Ionising radiation includes ultraviolet radiation, X-rays and gamma rays
Ionising Radiation Cell Damage Ionising radiation can damage living cells. Different amounts of ionising radiation can affect living cells. Physical barriers protect people from ionising radiation, for example, sun-screens and clothing can be used to absorb most of the ultraviolet radiation from the Sun.
Non-Ionising Radiation Can cause things to heat up. The heating effect of absorbed radiation can damage living cells This is due to it’s intensity and duration of exposure. Low intensity microwave radiation, for example from mobile phone hand sets and masts, may be a health risk, but this is disputed
Microwaves Microwaves heat materials containing particles that the microwaves can vibrate Metal cases and door screens of microwave ovens protect users from the radiation
Transmitting Information Infrared: Optical Fibres Microwaves: Mobile Phones Radio Waves: Television and Radio
Ozone Layer Ozone layer protects living organisms, especially animals, from the harmful effects ultraviolet radiation Ozone layer absorbs UV radiation, producing reversible chemical changes in that part of the atmosphere
Photosynthesis Photosynthesis removes carbon dioxide from the atmosphere and adds oxygen Photosynthesis and Respiration are opposites
Greenhouse Effect Earth emits EM radiation that is absorbed by some gases in the atmosphere, so keeping the Earth warmer than it would otherwise be.
Carbon Cycle For thousands of years the amount of carbon dioxide in the Earth’s atmosphere was fairly constant. For thousands of years there has been no burning fossil fuels or land use
Rising Carbon Dioxide in the Atmosphere During the past two hundred years, the amount of carbon dioxide in the atmosphere has been steadily rising. This is due to: 1.burning increased amounts of fossil fuels as an energy source 2.burning forests to clear land Both of these release carbon into the atmosphere that otherwise would have been locked up for many years
Decomposers Decomposers, such as microbes and fungi, play an important role in the carbon cycle. They break down the remains of dead plants and animals and, in doing so, release carbon dioxide through respiration.
Global Warming Most, but not all, scientists agree that the climate is getting gradually warmer. Most, but not all, scientists lay the blame for this on human activities increasing the amount of carbon dioxide in the atmosphere. Global warming could cause: 1.Climate change 2.Extreme weather conditions in some areas 3.Climate change may make it impossible to grow certain food crops in some regions. 4.Melting polar ice, and the thermal expansion of sea water, could cause rising sea levels and the flooding of low-lying land
Computer Climate Models One piece of evidence which supports the view of scientists who blame human activities for global warming has been provided by supercomputers. Computer climate models, based on different amounts of carbon dioxide in the atmosphere, produce the same changes as have been observed in the real world.
Factors and Outcomes Any process can be thought of in terms of factors that may affect an outcome. In global warming, one factor is the amount of carbon dioxide in the atmosphere. The outcome is the mean temperature of the atmosphere.
Correlation and Cause To establish a correlation between a factor and an outcome, convincing evidence is needed. This usually means that enough data must be collected, and that different samples should match. Compare these two graphs and consider these questions: 1.Are the changes reported significantly large? 2.Are they properly matched in terms of the times over which they are reported? 3.Do these two graphs match well enough?
Correlation and Cause A correlation between a factor and an outcome does not mean that the factor causes the outcome. They could both be caused by some other factor. Example – Children with bigger feet (factor) are, on average, better readers (outcome). – There is another factor which, in fact, causes both of these. It is age, because older children usually have bigger feet, and older children are usually better readers! – To investigate the relationship between a factor and an outcome, it is important to control all other factors that may affect the outcome.
Other factors affecting global warming Another factor that may affect the mean temperature of the atmosphere is the amount of energy given out by the Sun. Most scientists agree that this has not changed in the past 200 years. There are some scientists who agree that global warming is taking place, but do not agree that carbon dioxide levels are to blame.
Scientific Explanation Once experiments have shown that there is a definite correlation between a factor and an outcome, it is still not enough to prove that the factor causes the outcome. For this to be proven, there must be some scientific explanation of how the relationship can happen. For carbon dioxide and global warming, the explanation is that carbon dioxide is a greenhouse gas. It absorbs infrared given off by the warm Earth, and this infrared cannot then escape into space. This keeps the Earth warmer than it would be if the carbon dioxide did not absorb so much infrared.
Benefits and Risks It is impossible for anything to be completely safe. EG: getting sunlight each day can be beneficial (Vitamin D) but too much could cause skin cancer. Offer reasons for people’s willingness (or reluctance) to accept the risk of a given activity. EG: Getting a tan.
The Precautionary Principle The ‘precautionary principle’ tells you to avoid any activity if serious harm could arise. Parents may insist that their children are not allowed out on the beach at all in the summer months.
Real v Perceived Risk The real risk may be very different from the perceived risk ie: the risk that you think is there. – You can’t see ultraviolet, and the word ‘radiation’ sounds frightening to many people. This makes the risk seem worse than something you can see, and which is more familiar. – Some parents may assume that summers are no different from when they were young, so there is no danger to their children.
ALARA Principle The ALARA principle is to make any risk As Low As Reasonably Achievable. This usually applies to an organisation which is responsible for its employees. – A company employing lifeguards on the beach may insist that they wear lycra sun-suits and sun-screen cream to absorb ultraviolet when they are on duty – The company may also arrange that lifeguards take turns at covering the hottest part of the day, when the intensity of ultraviolet is greatest
Designing a Study Evaluate the design for a study to test whether or not a factor increases the chance of an outcome, by commenting on: 1.Sample size (the more people the better) 2.How well the samples are matched (both samples should be the same except for the variable that is being tested)