Tamil Nadu SSLC Science key terms

For every action force there is an equal and opposite reaction force, acting on a different body. A rocket pushes gas backwards and the gas pushes the rocket forwards.

The tendency of a body to resist any change in its state of rest or uniform motion. It depends only on mass, so a heavier object is harder to start or stop.

The product of a body's mass and its velocity, measured in kg m/s. It is a vector, so direction matters, and it is conserved when no external force acts.

The product of force and the time for which it acts, equal to the change in momentum. Cushioning increases the contact time and so reduces the force felt.

The distance from the pole of a spherical mirror or the optical centre of a lens to its principal focus. It equals half the radius of curvature for a mirror.

The point on the principal axis where rays parallel to the axis converge after reflection or refraction, or from which they appear to diverge for a diverging system.

The reciprocal of focal length in metres, expressed in dioptre. A converging lens has positive power and a diverging lens has negative power.

The ratio of the image height to the object height, which also equals the ratio of image distance to object distance for a mirror or lens using sign convention.

An image formed when light rays actually meet after reflection or refraction, so it can be caught on a screen and is always inverted.

At constant temperature, the current through a conductor is directly proportional to the potential difference across it, giving V = IR where R is the resistance.

The opposition a conductor offers to the flow of electric current, measured in ohm. It increases with length and temperature but decreases with greater cross-sectional area.

A property of the material of a conductor, equal to the resistance of a unit length with unit cross-sectional area. Its SI unit is the ohm metre.

A circuit in which components are joined end to end so the same current passes through each. The total resistance is the sum of the individual resistances.

A circuit in which components are connected across the same two points, so each has the full supply voltage. The reciprocal of total resistance is the sum of reciprocals.

Imaginary curves whose tangent at any point gives the direction of the magnetic field there. They run from north to south outside a magnet and never cross each other.

The production of an induced emf in a coil when the magnetic flux linked with it changes, as in moving a magnet near a coil or rotating a coil in a field.

The properties of elements are a periodic function of their atomic number, because chemical behaviour depends on the arrangement of electrons in shells.

A regular variation of a property across a period or down a group. Atomic radius falls across a period and rises down a group, while metallic character does the opposite.

The tendency of an atom in a molecule to attract the shared pair of electrons towards itself. It generally increases across a period and decreases down a group.

The combining capacity of an element, equal to the number of electrons it gains, loses or shares to complete its outermost shell. It is shown by the group number.

The electrostatic attraction between oppositely charged ions formed when one atom transfers electrons to another. Such compounds conduct electricity when molten or dissolved.

A bond formed by the sharing of one or more pairs of electrons between atoms, usually between non-metals. Shared pairs may be single, double or triple.

A scale from 0 to 14 measuring the hydrogen ion concentration of a solution. Values below 7 are acidic, 7 is neutral and above 7 is basic.

The reaction between an acid and a base to give salt and water, for example hydrochloric acid with sodium hydroxide giving sodium chloride and water.

A substance that changes colour with the acidity or basicity of a solution, such as litmus, methyl orange or phenolphthalein, and is used to detect acids and bases.

A family of organic compounds with the same functional group and general formula, in which successive members differ by one CH2 unit and show gradual change in properties.

An atom or group of atoms attached to a carbon chain that decides the characteristic chemical properties of a compound, such as OH in alcohols or COOH in acids.

The existence of two or more compounds with the same molecular formula but different arrangements of atoms, giving them different physical and chemical properties.

The movement of water molecules across a semipermeable membrane from a region of higher water concentration to one of lower water concentration, without using energy.

The shrinking of the protoplasm away from the cell wall when a plant cell loses water in a strong solution, showing that the membrane is semipermeable.

The spontaneous spreading of particles from a region of higher concentration to one of lower concentration, as when oxygen moves from air into the blood.

The process by which green plants use light energy to convert carbon dioxide and water into glucose and oxygen, with chlorophyll acting as the trapping pigment.

The loss of water as vapour from the aerial parts of a plant, mainly through stomata, which helps in pulling water upwards and cooling the leaf.

The two alleles of a gene separate during gamete formation so that each gamete carries only one allele, which reunites randomly at fertilisation.

The form of a gene that expresses its effect in a heterozygote, hiding the effect of the recessive allele. It is written with a capital letter.

The observable characteristics of an organism, such as flower colour or seed shape, produced by the interaction of its genotype with the environment.

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

An inherited feature or behaviour that improves an organism's chance of surviving and reproducing in its particular habitat, formed over many generations.

A sequence of organisms in which each is eaten by the next, starting with a producer and ending with a top consumer, and along which energy flows.

The position an organism occupies in a food chain, such as producer, primary consumer or secondary consumer. Only about ten per cent of energy passes to the next level.

The ability of the body to resist infection by a pathogen, either inborn or acquired after infection or vaccination through the production of antibodies.

The introduction of weakened or killed pathogens or their products into the body to stimulate antibody production and create memory cells for future protection.

How close a measured value is to the true value of the quantity. A measurement can be precise yet inaccurate if a systematic error is present.

How closely repeated measurements of the same quantity agree with one another, which depends on the instrument and the observer rather than on the true value.

The smallest measurement an instrument can read, for example 1 mm for an ordinary ruler or 0.01 mm for a vernier scale, which limits the precision.