AP SSC General Science (BSEAP) key terms

The line drawn perpendicular to a mirror or refracting surface at the exact point where the light ray strikes it. All angles in reflection and refraction are measured from this line, not from the surface itself.

The point on the mirror's principal axis where rays travelling parallel to the axis converge after reflection. It lies in front of the mirror at half the radius of curvature.

The distance from the pole of a spherical mirror or lens to its principal focus. For a spherical mirror it equals half the radius of curvature; for a lens it sets the image position in the lens formula.

The centre of the sphere of which a curved mirror or lens surface forms a part. It lies on the principal axis, and the distance from pole to this point is the radius of curvature.

The ratio of the height of the image to the height of the object. It also equals the ratio of image distance to object distance, with a negative sign for mirrors using the sign convention.

An image formed when reflected or refracted rays actually meet, so it can be caught on a screen. It is always inverted relative to the object and may be larger or smaller.

An image formed when rays only appear to diverge from a point and do not actually meet. It cannot be caught on a screen and is erect, as seen in a plane mirror or magnifying glass.

The angle between the incident ray and the normal at the point of incidence. It is measured inside the denser or rarer medium depending on the surface, and in reflection it equals the angle of reflection.

The ratio of the speed of light in vacuum to its speed in a given medium. A higher value means light slows more and bends more strongly when entering that medium from air.

The angle between the refracted ray and the normal inside the second medium. It relates to the angle of incidence through Snell's law and the refractive indices of the two media.

The complete bouncing back of light into a denser medium when it strikes the boundary with a rarer medium beyond the critical angle. It causes mirages and makes optical fibres work.

The angle of incidence in the denser medium for which the refracted ray grazes along the boundary between the two media. Beyond it, total internal reflection occurs instead of refraction.

The splitting of white light into its component colours because each colour has a slightly different refractive index in a medium. A glass prism produces a spectrum this way.

The redirection of light in many directions by tiny particles in a medium. It makes the sky blue, sunsets red, and makes the Tyndall effect visible in colloidal mixtures.

The ability of the eye's ciliary muscles to change the curvature of the lens so that objects at different distances focus clearly on the retina. It decreases with age, causing presbyopia.

Short-sightedness in which distant objects appear blurred because the image forms in front of the retina. It is corrected using a concave lens of suitable power.

Long-sightedness in which nearby objects appear blurred because the image forms behind the retina. It is corrected using a convex lens that converges light before it enters the eye.

The combining capacity of an element, equal to the number of electrons it gains, loses, or shares to complete its outermost shell. It determines the formula of compounds formed.

The electrostatic attraction formed between oppositely charged ions after one atom transfers electrons to another. It typically forms between a metal and a non-metal and gives high melting points.

A bond formed when two atoms share one or more pairs of electrons to attain stable outer shells. It usually joins non-metal atoms, as in water, methane, and carbon dioxide.

An equation in which the number of atoms of each element is equal on both the reactant and product sides. Mass is conserved, and coefficients are adjusted, never subscripts.

A reaction in which two or more substances combine to form a single product. Examples include burning magnesium in oxygen and quicklime reacting with water.

A reaction in which a single compound breaks down into two or more simpler substances, usually on heating, electrolysis, or exposure to light. Calcium carbonate on heating gives quicklime and carbon dioxide.

A reaction in which a more reactive element pushes out a less reactive element from its compound. Iron nails dipped in copper sulphate solution turning brownish is a common example.

A reaction in which two compounds exchange ions to form two new compounds, often producing a precipitate. Silver nitrate solution with sodium chloride solution giving white silver chloride is an example.

An insoluble solid that separates from a solution during a chemical reaction. Its appearance, such as a white or yellow solid, is often used as evidence that a reaction has occurred.

A scale from 0 to 14 expressing how acidic or basic a solution is, based on hydrogen ion concentration. Values below 7 are acidic, 7 is neutral, and above 7 is basic.

The reaction between an acid and a base that produces a salt and water. The acidic and basic properties are destroyed, and the resulting solution may be neutral or slightly acidic or basic.

A substance that changes colour to show whether a solution is acidic or basic. Litmus, methyl orange, and phenolphthalein are common examples used in school laboratories.

A list of metals arranged in decreasing order of chemical reactivity. It predicts whether a displacement reaction occurs and helps explain how metals are extracted from their ores.

The process of heating an ore strongly in the absence or limited supply of air to remove moisture and volatile impurities, and to convert carbonates to oxides. It is used for carbonate ores.

The process of heating a sulphide ore strongly in a plentiful supply of air so that it is converted to an oxide. The oxide can then be reduced to obtain the metal.

A family of carbon compounds with the same functional group and similar chemical properties, in which successive members differ by one carbon and two hydrogen atoms. Alkanes and alcohols form such series.

The specific atom or group of atoms attached to a carbon chain that gives a compound its characteristic chemical properties. Alcohols, aldehydes, ketones, and carboxylic acids each have a distinct one.

One of two or more compounds that have the same molecular formula but different arrangements of atoms, and therefore different properties. Butane and isobutane are simple examples.

The statement that the current through a conductor is directly proportional to the potential difference across it, provided temperature stays constant. The constant of proportionality is the resistance.

The opposition a conductor offers to the flow of electric current, measured in ohms. It depends on the material, length, and thickness of the conductor and on its temperature.

The rate at which electrical energy is consumed or delivered in a circuit, measured in watts. It equals the product of potential difference and current, and also current squared times resistance.

In a pair of contrasting characters, the dominant trait appears in the offspring even when only one copy is present, while the recessive trait appears only when both copies are recessive. Mendel explained this using pea plants.

Genotype is the genetic makeup of an organism for a trait, while phenotype is the observable characteristic it shows. Different genotypes can produce the same phenotype when a dominant allele is present.