Bihar BSEB Matric Science key terms

A way of writing a chemical reaction in which the number of atoms of every element is equal on the reactant and product sides. Coefficients are changed to balance it; subscripts inside formulae are never altered.

A change in which a substance gains oxygen, loses hydrogen, or gives up electrons. Burning of magnesium in air and the rusting of iron are everyday examples.

A change in which a substance loses oxygen, gains hydrogen, or takes up electrons. It always occurs together with oxidation, as when zinc oxide is heated with carbon.

The unpleasant smell and taste that develop in fats and oils when their molecules are oxidised by air. Antioxidants, airtight packing and refrigeration slow this spoilage down.

A numbered scale from 0 to 14 that expresses how acidic or basic a solution is. Values below 7 are acidic, 7 is neutral, and values above 7 are basic.

The reaction between an acid and a base that produces a salt and water. The acidic and basic properties cancel each other, so the resulting solution is closer to neutral.

A dye or substance that changes colour when added to an acidic or basic solution, letting you judge its nature. Litmus, methyl orange and phenolphthalein are common examples.

An arrangement of metals in order of decreasing chemical reactivity. It predicts whether a metal will displace another from a salt solution and how vigorously it reacts with water or acids.

A solid mixture made by melting a metal with one or more other elements to improve properties such as strength, hardness or resistance to rusting. Steel, brass and bronze are common examples.

The slow wearing away of a metal surface by air, moisture or chemicals, producing oxides or salts. Rusting of iron and the green coating on copper are typical examples.

The ability of atoms of an element to link with other atoms of the same element, forming long chains or rings. Carbon shows this strongly, which explains the huge number of carbon compounds.

A family of carbon compounds having the same functional group, in which successive members differ by one carbon and two hydrogen atoms, so physical properties change gradually while chemical behaviour stays similar.

An atom or group of atoms attached to a carbon chain that gives the compound its characteristic chemical properties. Examples are alcohol (-OH), carboxylic acid (-COOH) and aldehyde (-CHO).

The statement that properties of elements are periodic functions of their atomic number. It replaced the atomic-mass basis of earlier tables and explains why elements of a group behave similarly.

The ratio of the speed of light in vacuum to its speed in a given medium. A higher value means the medium bends light more strongly and light travels more slowly inside it.

The point on the principal axis of a lens or spherical mirror where rays travelling parallel to the axis meet, or appear to meet, after refraction or reflection.

A measure of how strongly a lens converges or diverges light, equal to the reciprocal of its focal length measured in metres. It is expressed in dioptres.

The ability of the eye to change the focal length of its lens so that objects at different distances are focused clearly on the retina. The ciliary muscles bring this about.

The splitting of white light into its component colours when it passes through a refracting medium such as a glass prism, because different colours are bent by different amounts.

The redirection of light in many directions when it strikes tiny particles such as dust or gas molecules. It makes the sky appear blue and sunsets appear red.

The work done in moving a unit charge between two points of a circuit, measured in volts. It is the electrical push that drives current through a conductor.

The property of a conductor that opposes the flow of electric current through it. It depends on length, area of cross-section, material and temperature, and is measured in ohms.

The rate at which electrical energy is transferred or consumed in a circuit, equal to the product of voltage and current. It is measured in watts.

The region around a magnet or a current-carrying conductor where its magnetic force can be detected. It is represented by field lines whose direction outside the magnet runs from north to south.

A coil of insulated wire wound in the shape of a cylinder. When current flows through it, it behaves like a bar magnet, and with a soft iron core it becomes an electromagnet.

The production of an electric current in a coil when the magnetic field linked with it changes, for example when a magnet is moved near it. Generators work on this principle.

A natural source of energy or material that natural processes can replenish within a short time, such as sunlight, wind, flowing water and biomass. Continuous use does not exhaust it.

A mixture consisting mainly of methane and carbon dioxide, produced when organic waste such as cattle dung or plant residue is decomposed by bacteria in the absence of air. It burns cleanly for cooking and lighting.

The process by which green plants use sunlight, carbon dioxide and water to make glucose and release oxygen, with chlorophyll absorbing the light energy needed for the reaction.

The tiny filtering unit of the kidney. Each kidney contains a very large number of them, and together they remove urea and excess water and salts from blood to form urine.

A quick, automatic response to a stimulus that does not need conscious thought, such as pulling the hand away from a hot object. It is coordinated by the spinal cord.

A chemical messenger secreted in small amounts by an endocrine gland and carried by blood to a target organ, where it regulates growth, metabolism or reproduction. Insulin and thyroxine are examples.

The transfer of pollen grains from the anther to the stigma of a flower. It may be brought about by wind, water, insects or other animals, and is followed by fertilisation.

A form of asexual reproduction in plants in which a new plant grows from a part such as a stem, root or leaf, for example from potato tubers or sugarcane cuttings.

The form of a character that appears in an organism whenever at least one copy of the controlling gene is present, masking the effect of the recessive form of the same gene.

The process by which individuals with variations better suited to their surroundings survive and reproduce more successfully, so those useful traits become more common in later generations.

A series of organisms in which each one feeds on the one before it, showing how energy and matter pass from producers to herbivores and then to carnivores.

The rise in concentration of a harmful substance in the bodies of organisms at each higher level of a food chain, because that substance is not broken down or excreted.

Development that meets present-day needs without using resources so fast that future generations cannot meet theirs. It balances economic growth with care for the environment.