Tag: o level revision notes

Human life is enhanced by structures. Every structure has a design that makes it best suited for its purpose and the material chosen to make the structure must have suitable properties.  Beams are used to carry loads.  A truss is made up of several beams joined together.  Different building materials have their advantages and disadvantages. There are a variety of methods of joining materials.

Solar energy refers to energy from sun. Solar energy has three main components; visible light, infrared radiation and ultraviolet radiation. Visible light enables us to see, ultraviolet radiation enables the skin to produce vitamin D while infrared (radiant heat) warms up objects and heats up any object which absorbs it. Solar energy absorbed by plants enables them to manufacture food through the process of photosynthesis. When solar energy strikes an object, it is either reflected if surface is polished, e.g. a mirror or it is absorbed.

There are negative and positive charges. Like charges repel while opposite charges attract. Materials can be rubbed or brushed to transfer charge to them.  Lightning is the result of movement of electrical charge from the clouds to the ground. Current electricity is the result of flowing charge. Cells convert chemical energy into electrical energy. Electrical energy is hazardous and safety precautions should be observed when it is used.

Fuels are materials that are burnt to provide heat or chemical energy. Fuels can be gases, liquids or  solids. There are natural and man-made fuels. Some fuels are more efficient than others. Engines are machines designed to convert chemical energy into other forms of energy and thus do work. The use of fuels has social and economic implications on society. Fuels are either renewable or non-renewable. Non-renewable fuels should be used sustainably.

Industrial processes involve production on a large scale. Large sites and machinery are used for the production of useful gases, acids and fertilisers. There are three industrial processes that candidates must be familiar with namely: Contact process , Haber process and Catalytic oxidation of ammonia.

Iron and copper are widely used metals.  Iron and copper exist in the environment as iron ore and copper. In order to get pure iron and copper the ores must be smelted. The removal of impurities involves chemical reactions.  Iron has the following processes: extraction. Copper and iron can be combined with other metals to form alloys.  Metals can be coated to prevent rusting.

Materials in all forms, i.e. solids, liquids and gases are all made up of matter. All matter is made up of atoms. Atoms are made up of three types  particles, the protons, neutrons and electrons. Matter can exist as elements, mixtures and compounds. Materials can be classified as metals or non-metals. Some metals are more reactive than others. Some materials are acids bases or salts. Speeds of reaction are affected by temperature, concentration, surface area and the presence of catalysts.

An ecosystem is a self-contained system of interdependent organisms and their physical environment. An ecosystem has various components that may include air, water, soil, light and living organisms.

Plants of the same species are different. The difference between organisms of the same species is called variation. There are two types of variation: continuous and discontinuous. Variation is either inherited or caused by the environment. Man is interested in variation and seeks to manipulate it to produce good quality crops and livestock.  Selection is the process of eliminating individuals with undesirable characteristics.  Selection can be natural or artificial.