RBSE Praveshika Science flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Sublimation

The direct change of a solid into vapour without passing through the liquid state, seen in camphor, iodine, naphthalene and dry ice; the reverse process is called deposition.

Latent heat of fusion

The heat required to change 1 kg of a solid at its melting point into liquid with no rise in temperature; for ice it is about 3.34 × 10⁵ J/kg.

Brownian motion

The random zig-zag movement of tiny particles suspended in a fluid, caused by unequal collisions with fast-moving molecules; it is direct evidence that matter is particulate.

Newton's second law

The rate of change of momentum of a body is directly proportional to the applied unbalanced force and occurs in the direction of the force, giving F = ma.

Conservation of momentum

In an isolated system with no external force, the total momentum before a collision equals the total momentum after it; this follows from Newton's third law.

Universal gravitational constant G

The force of attraction between two 1 kg masses placed 1 m apart; its value is 6.67 × 10⁻¹¹ N m² kg⁻² and it is the same everywhere in the universe.

Centripetal acceleration

The acceleration of a body moving uniformly on a circular path, directed towards the centre; its magnitude is v²/r and it changes direction, not speed.

Work in physics

Work is done when a force moves a body along its own direction; W = F s cos θ, measured in joules, and it is zero when force is perpendicular to displacement.

Law of conservation of energy

Energy can neither be created nor destroyed; it only changes from one form to another, so the total energy of an isolated system remains constant.

Echo

A sound heard again after reflection from a distant hard surface; it needs a delay of at least 0.1 s, so the reflector must be about 17 m away in air.

Real image

An image formed where reflected or refracted rays actually meet; it can be caught on a screen and is always inverted, as produced by a concave mirror or convex lens.

Refractive index

The ratio of the speed of light in vacuum to its speed in a medium, equal to sin i / sin r; it is 1.33 for water and about 1.5 for glass.

Power of a lens

The reciprocal of the focal length measured in metres, expressed in dioptres; it is positive for a convex lens and negative for a concave lens.

Ohm's law

At constant temperature, the current through a metallic conductor is directly proportional to the potential difference across its ends, so V = IR with R in ohms.

Electric power

The rate at which electrical energy is consumed; P = VI = I²R = V²/R, measured in watts, and 1 kWh equals one commercial unit of energy.

Fleming's left-hand rule

If the thumb, forefinger and middle finger of the left hand are stretched mutually perpendicular, they give the directions of force, magnetic field and current in a motor.

Decomposition reaction

A reaction in which one compound breaks down into two or more simpler substances, usually by heat, electricity or light, as in CaCO₃ → CaO + CO₂.

Redox reaction

A reaction in which one substance is oxidised by losing electrons or gaining oxygen while another is reduced by gaining electrons or losing oxygen at the same time.

Catalyst

A substance that changes the rate of a chemical reaction without being used up or changing its own mass and composition; enzymes are biological catalysts.

Neutralisation reaction

The reaction between an acid and a base giving salt and water; the H⁺ of the acid combines with the OH⁻ of the base and the solution moves towards pH 7.

pH scale

A scale from 0 to 14 measuring hydrogen ion concentration: below 7 is acidic, exactly 7 neutral and above 7 basic; each unit means a tenfold change.

Baking soda

Sodium hydrogen carbonate, NaHCO₃, a mild base used in cooking and antacids; on heating it gives sodium carbonate, water and carbon dioxide.

Reactivity series

An arrangement of metals in decreasing order of chemical reactivity from potassium to gold; a metal higher in the list displaces one lower from its salt solution.

Amphoteric oxide

A metal oxide that reacts with both acids and bases to form salts, for example aluminium oxide and zinc oxide.

Homologous series

A family of organic compounds with the same functional group and general formula, in which successive members differ by one carbon and two hydrogen atoms.

Reflex action

A rapid automatic response to a stimulus in which the message is routed through the spinal cord without waiting for the brain to decide.

Xylem

Vascular tissue that carries water and dissolved minerals upwards from the roots to the leaves in plants; its vessels are dead, hollow and thickened with lignin.

Insulin

A hormone secreted by the beta cells of the pancreas that lowers blood glucose by increasing its uptake by cells and promoting storage as glycogen in the liver.

Mendel's law of dominance

When two pure contrasting forms are crossed, only one trait, the dominant one, appears in the first filial generation while the recessive trait stays hidden.

Natural selection

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

Food chain

A sequence of organisms in which each is eaten by the next, showing energy transfer from producers through herbivores to carnivores; only about 10% passes on.

Ozone layer

A layer of O₃ in the stratosphere that absorbs harmful ultraviolet radiation from the Sun; it is damaged by chlorofluorocarbons and other halogen compounds.