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Faraday’s Law of Electromagnetic Induction states that the electromotive force induced in a conductor is proportional to the rate of change of magnetic flux linkages through the conductor.
(Memorise it! It is useful when trying to explain the effects caused by Faraday’s Law)
Lenz’s Law states that the direction of the induced e.m.f. and hence the induced current in a closed circuit, is always such that its magnetic effect opposes the motion or change producing the induced e.m.f.
(Memorise it! It is useful when trying to explain the effects caused by Lenz’s Law)
An electrostatic precipitator (ESP) is a device that removes particulate matter from exhaust gases using electrostatic forces. It is commonly used in industries such as power plants, cement factories and steel mills to control air pollution.
The basic principle of an ESP is to use an electric field to charge the solid particles in the gas stream, and then collect them on a charged surface.
1. The gas stream is first passed through a series of electrodes, which are typically made of metal wires or plates. These electrodes are charged with a high voltage, usually in the range of tens of thousands of volts.
2. As the gas stream passes through the electrodes, the solid particles in the gas become charged, either positively or negatively depending on the polarity of the electrodes. The charged particles are then attracted to an oppositely charged collection electrode, which is usually a flat metal plate or a series of plates.
3. As the particles collect on the collection electrode, they form a layer of solid deposits that can be removed periodically. This is done by rapping on the collection plates, which causes the solid deposits to fall into a hopper or other collection device.
Energy can be transferred from one store to another:
i) Mechanically (by a force acting over a distance)
Eg: a car moving up an inclined plane
(chemical potential energy –> gravitational potential energy)
ii) Electrically (by an electric current)
Eg: lighting up a bulb in an electric circuit
(chemical potential energy of battery –> light and heat energy of light bulb)
iii) By heating (due to a temperature difference)
Eg: a gas stove heating up a pot of water
(chemical potential energy of gas –> internal energy of water)
iv) By propagation of waves (both electromagnetic and mechanical)
Eg: a dipper producing surface water waves
(mechanical energy of dipper –> kinetic energy of water waves)
An energy store is a substance or a physical system that can store energy in various forms.
Some examples of energy stores are:
– batteries (chemical potential energy)
– a stretched spring (elastic potential energy)
– fuels (chemical potential energy)
– a dammed water body (gravitational potential energy)
– tidal waves (kinetic energy)
– radioactive isotopes (nuclear energy)
Depolymerisation is a process which involves breaking down the plastic polymer into its monomer units. The monomers can then be purified and used to create new plastics.
An example is the hydrolysis of polyesters using acid as a catalyst.
In the hydrolysis process, the ester linkages that hold the polymer chains together are broken. The polyesters will be broken down to form a large number of dicarboxylic acid monomers and diol monomers.
Conditions for hydrolysis of polyesters:
– An acid catalyst, usually sulfuric acid or hydrochloric acid
– Water as a reactant
– High temperature of between 80 deg C to 150 deg C
Increased greenhouse gas concentrations trap more heat in the Earth’s atmosphere, causing the average temperature on Earth to increase. This phenomenon is known as global warming. Global warming can result in more extreme weather events and the melting of polar ice.
1. Melting of ice caps and glaciers
The rising temperatures can cause ice caps and glaciers to melt, resulting in rising sea levels and increased flooding in low-lying coastal regions.
2. Extreme weather events
The rising temperatures can cause changes in precipitation patterns, resulting in more intense and frequent rainfall in some regions and more frequent and severe droughts in other regions. There will be more frequent and intense heat waves, droughts and extreme weather events like hurricanes and floods.
Greenhouse gases are gases that trap heat in the Earth’s atmosphere. Examples of greenhouse gases are carbon dioxide and methane. Too much of these greenhouse gases can result in global warming.
The sources of these gases:
1. Carbon dioxide
Carbon dioxide is released to the atmosphere mainly through the combustion of carbon-containing fuels, and the respiration of living organisms.
2. Methane
Methane is released to the atmosphere mainly through the decomposition of organic matter and from flatulence from livestock like cows, goats.
1. Physical Method
The physical method used in recycling plastics involves physically breaking down the plastics into very small pieces. The plastics are physically crushed into smaller pieces and blended to form a mixture of uniform homogenous quality. The blended mixture is melted and passed through a screen to form strands. This is known as extrusion. After cooling, the plastic strands are cut into pellets to be used as materials for new products.
2. Chemical Method
The chemical methods used in recycling plastics involve chemically breaking down the long-chain molecular structure in plastics into smaller molecules.
Cracking of plastics and depolymerisation of plastics are the two common chemical methods of recycling plastics.
i. Cracking of plastics
Cracking of plastics involves heating the plastic waste to high temperatures in the presence of a catalyst. The long-chain molecules are broken down into smaller molecules. This process transformed the plastic waste into a mixture of gases, liquids and solids. This mixture is then separated and processed to create new raw materials or fuels.
ii. Depolymerisation of plastics
This process involves breaking down the plastic polymer into its monomer units. The monomers can then be purified and used to create new plastics.
1. Biofuel is a renewable and sustainable energy source, while crude oil is non-renewable. Food crops like palm oil or sugarcane can be replenished in a relatively short period of time. Food wastes are readily available and in abundance in big, populated cities. Biofuel made from these sources is renewable and sustainable.
In contrast, crude oil reserves are depleting fast and are projected to run out in decades.
2. Biofuel from food crops is a cleaner source of energy as the carbon dioxide released during its combustion will be offset by the carbon dioxide absorbed during photosynthesis carried out over the food crops’ lifetime.
Crude oil, when combusted, produces air pollutants like sulfur dioxide, and releases carbon dioxide which is not offset by carbon dioxide absorption during photosynthesis.