Jharkhand Polytechnic (PECE) key terms

The internationally agreed standard unit used to express a physical quantity, such as the metre for length or the newton for force. Answers in numerical physics problems should normally be quoted in these units.

An expression showing which base quantities (mass, length, time, current, temperature, amount, luminous intensity) make up a derived quantity, written with exponents, for example force as [M L T⁻²]. Used to check equation correctness.

A scalar has magnitude only, such as mass, time or temperature. A vector has both magnitude and direction, such as displacement, velocity or force, and adds by the triangle or parallelogram rule rather than simple arithmetic.

The single vector that produces the same effect as two or more vectors acting together. For perpendicular vectors it is found using the Pythagorean relation, and its direction from the tangent of the angle.

The change in position of an object measured as a straight line from start to finish, including direction. It differs from distance travelled, which is the total path length and is always positive.

The rate at which velocity changes with time, measured in metres per second squared. It occurs whenever speed changes, direction changes, or both, and can be positive or negative.

The net force on a body equals the rate of change of its momentum, which for constant mass reduces to force equals mass times acceleration. It links force, mass and acceleration in one equation.

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 body needs a larger force to produce the same acceleration.

The product of a body's mass and velocity, a vector quantity measured in kilogram metre per second. In an isolated system the total momentum before and after a collision stays constant.

The principle that energy can be transferred or transformed but never created or destroyed. In mechanics it means the sum of kinetic and potential energy stays constant when only conservative forces act.

The rate at which work is done or energy is transferred, measured in watts, where one watt equals one joule per second. It equals force multiplied by velocity for motion at constant speed.

The curved path followed by an object thrown into the air and moving under gravity alone. Horizontal and vertical motions are treated separately, giving a parabolic trajectory when air resistance is ignored.

The ratio of the speed of light in vacuum to its speed in a medium, always at least one. It determines how strongly a ray bends when entering or leaving the medium.

The complete reflection of light back into a denser medium when it strikes the boundary at an angle greater than the critical angle. It is the principle behind optical fibres and sparkling diamonds.

The distance from the pole of a lens or mirror to its principal focus, where parallel rays converge or appear to diverge. It fixes the power of the lens and the position of images.

The statement that the current through a metallic conductor is directly proportional to the potential difference across it, provided temperature stays constant. It gives the relation voltage equals current times resistance.

A property of a material, not of a particular wire, measuring how strongly it opposes current flow. It equals resistance times cross-sectional area divided by length, with unit ohm metre.

The rate at which electrical energy is converted in a circuit, equal to voltage times current or to current squared times resistance. It is measured in watts and billed in kilowatt hours.

The amount of substance containing exactly the Avogadro number of elementary particles, about 6.022 × 10²³. It links the mass of a sample to the number of atoms or molecules it contains.

The mass of one mole of a substance in grams per mole, numerically equal to its formula mass in atomic mass units. It converts between mass and moles in stoichiometric calculations.

The number of particles in one mole of any substance, approximately 6.022 × 10²³ per mole. It allows individual particle counts to be related to measurable masses.

The calculation of quantities of reactants and products from a balanced chemical equation using mole ratios. It predicts limiting reagents, theoretical yields and volumes of gases involved.

The reactant that is completely consumed first and therefore decides the maximum amount of product formed. Others are present in excess and remain partly unreacted.

Oxidation is loss of electrons or increase in oxidation number; reduction is gain of electrons or decrease in oxidation number. The two always occur together in a redox reaction.

A bookkeeping number showing the charge an atom would carry if its bonds were fully ionic. Rules assign values so that the sum over a neutral compound is zero and over an ion equals its charge.

The decomposition of an electrolyte by passing direct current through its solution or melt, producing chemical change at the electrodes. Oxidation occurs at the anode and reduction at the cathode.

A logarithmic scale from 0 to 14 expressing the acidity of an aqueous solution as the negative logarithm of hydrogen ion concentration. Values below 7 are acidic, 7 neutral and above 7 basic.

A solution that resists large changes in pH when small amounts of acid or base are added, usually made from a weak acid with its salt or a weak base with its salt.

The reaction between an acid and a base producing salt and water, with the hydrogen ions of the acid combining with hydroxide ions of the base. The resulting pH depends on the strength of both.

The mixing of atomic orbitals of similar energy to form new equivalent orbitals that explain observed molecular geometry, such as sp, sp² and sp³ arrangements in carbon compounds.

The existence of two or more compounds with the same molecular formula but different structures or spatial arrangements, leading to different physical and chemical properties.

A chemical bond formed by the sharing of one or more pairs of electrons between atoms, typically between non-metals. It may be non-polar or polar depending on electronegativity difference.

A regular variation in properties such as atomic radius, ionisation energy or electronegativity across a period or down a group of the periodic table, explained by nuclear charge and shielding.

A single number computed from a square matrix that indicates whether the matrix is invertible. A zero determinant means the system of equations has no unique solution.

A rectangular arrangement of numbers in rows and columns, written with brackets. Matrices are added element-wise and multiplied only when the column count of the first equals the row count of the second.

The matrix that multiplies a given square matrix to give the identity matrix. It exists only when the determinant is non-zero, and is used to solve simultaneous equations.

The instantaneous rate of change of a function with respect to its variable, defined as the limit of the difference quotient. Geometrically it gives the slope of the tangent to the curve.

The reverse process of differentiation, used to find a function from its rate of change or to compute the area under a curve. Definite integrals give numerical values between two limits.

The value a function approaches as its input approaches a given point, whether or not the function is defined there. Limits underpin both continuity and the definitions of derivative and integral.

A sequence in which each term differs from the previous one by a fixed constant called the common difference. Its nth term and sum are found with standard formulas.

A sequence in which each term is obtained by multiplying the previous term by a fixed ratio. Sums of finite and infinite terms are found with standard formulas.

Permutations count arrangements where order matters, while combinations count selections where order does not. Both use factorials and are applied to probability and counting problems.

A number between zero and one expressing how likely an event is, calculated for equally likely outcomes as favourable outcomes divided by total outcomes. Complement and addition rules combine events.

The supreme law of the country, adopted in 1949 and enforced from 26 January 1950, laying down fundamental rights, directive principles and the structure of government.

Basic rights guaranteed to citizens in Part III of the Indian Constitution, such as equality, freedom of speech and protection from exploitation, enforceable through writs in courts.

The three-tier system of local self-government in rural India at village, block and district levels, given constitutional status by the 73rd Amendment Act of 1992.

The latitude about 23.5 degrees north of the equator, the northern limit where the sun appears directly overhead. It passes through several Indian states including Jharkhand's neighbouring regions.

A seasonal reversal of wind direction bringing heavy rainfall, most importantly the south-west monsoon from June to September that provides most of India's annual precipitation.

An elevated area of relatively flat land raised above the surrounding region, often bounded by steep slopes. The Chota Nagpur Plateau forms most of Jharkhand and is rich in minerals.

A form of logical reasoning with two or more premises leading to a conclusion, tested by checking which conclusions necessarily follow. Venn diagrams are commonly used to solve such questions.

A reasoning question presenting a pair of related items and asking for another pair with the same relationship. The hidden relation may involve function, category, degree or sequence.

A question giving a sequence of numbers, letters or figures following a pattern, with one element missing or wrong. The rule must be identified from the given terms.

A reasoning topic where words or numbers are converted into a code by a consistent rule, and the candidate must apply the same rule to a new word or decipher the original.

A reasoning puzzle describing family relationships in words or symbols, requiring the candidate to work out how two people are related. Drawing a family tree helps avoid confusion.

A word having the same or nearly the same meaning as another word in the same language, such as begin and commence. Synonym questions test vocabulary depth rather than grammar.

A word expressing the opposite meaning of another word, such as ancient and modern. Antonym questions require recognising contrast in meaning, not just unfamiliar vocabulary.

A fixed expression whose meaning cannot be worked out from its individual words, such as to let the cat out of the bag meaning to reveal a secret.

Two ways of presenting a clause: active voice makes the doer the subject, passive voice makes the receiver the subject and uses a form of be with the past participle.

Two ways of reporting someone's words: direct speech quotes them exactly in quotation marks, while indirect speech reports them without quotes and shifts tense and pronouns.

The grammar rule that a verb must match its subject in number and person, so a singular subject takes a singular verb. Collective nouns and phrases between them often cause errors.